Yi-chuan Su Thesis (PDF 10MB)

I

Theoretical and Experimental Characterisation

of Energy in an Electrostatic Discharge

Yi-chuan Su

BEng, PhD Cand.

Submitted in fulfilment of the requirements for the degree of

Doctor of Philosophy

Science and Engineering Faculty

Queensland University of Technology

March, 2013

Theoretical and Experimental Characterisation of Energy in an Electrostatic Discharge

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Student: Yi-chuan Su

Student number: 04712382

[email protected]

Principal Supervisor

Prof. T. Steinberg

[email protected]

BE (Mech), MSc, PhD, CPEng, RPEQ, SMIEAust

Associate supervisor

Dr. J. Lyall

[email protected]

BE, BSc, ME, PhD

Associate Supervisor

Dr. M. Castillo

[email protected]

BE, PhD


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Keywords:

Electrostatic discharge; High impedance measurement circuit, Minimum ignition energy, N-

pentane, Spark energy, and Spark discharge.


V

Acknowledgements

This research work would not have been possible without the assistance and guidance of my

supervisors Prof. Ted Steinberg, A/Prof. Jim Lyall and Dr. Martin Castillo. Their support and

encouragement throughout the research journey is greatly appreciated.

Special thanks to Mate Frankic, Wolfgang Maier, Anthony Tofoni, Eric Klokman and Ken

McIvor of the Electrical Engineering Technician Team at SEF/QUT (EESE/BEE). Their

technical advice has allowed this project to succeed.


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Abstract

Electrostatic discharges have been identified as the most likely cause in a number of incidents

of fire and explosion with unexplained ignitions. The lack of data and suitable models for this

ignition mechanism creates a void in the analysis to quantify the importance of static

electricity as a credible ignition mechanism. Quantifiable hazard analysis of the risk of

ignition by static discharge cannot, therefore, be entirely carried out with our current

understanding of this phenomenon.

The study of electrostatics has been ongoing for a long time. However, it was not until the

wide spread use of electronics that research was developed for the protection of electronics

from electrostatic discharges. Current experimental models for electrostatic discharge

developed for intrinsic safety with electronics are inadequate for ignition analysis and

typically are not supported by theoretical analysis.

A preliminary simulation and experiment with low voltage was designed to investigate the

characteristics of energy dissipation and provided a basis for a high voltage investigation. It

was seen that for a low voltage the discharge energy represents about 10% of the initial

capacitive energy available and that the energy dissipation was within 10 ns of the initial

discharge. The potential difference is greatest at the initial break down when the largest

amount of the energy is dissipated. The discharge pathway is then established and minimal

energy is dissipated as energy dissipation becomes greatly influenced by other components

and stray resistance in the discharge circuit. From the initial low voltage simulation work, the

importance of the energy dissipation and the characteristic of the discharge were determined.

After the preliminary low voltage work was completed, a high voltage discharge experiment

was designed and fabricated. Voltage and current measurement were recorded on the

discharge circuit allowing the discharge characteristic to be recorded and energy dissipation

in the discharge circuit calculated. Discharge energy calculations show consistency with the

low voltage work relating to discharge energy with about 30-40% of the total initial

capacitive energy being discharged in the resulting high voltage arc.

After the system was characterised and operation validated, high voltage ignition energy

measurements were conducted on a solution of n-Pentane evaporating in a 250 cm3 chamber.


VII

A series of ignition experiments were conducted to determine the minimum ignition energy

of n-Pentane. The data from the ignition work was analysed with standard statistical

regression methods for tests that return binary (yes/no) data and found to be in agreement

with recent publications

The research demonstrates that energy dissipation is heavily dependent on the circuit

configuration and most especially by the discharge circuit’s capacitance and resistance. The

analysis established a discharge profile for the discharges studied and validates the

application of this methodology for further research into different materials and atmospheres;

by systematically looking at discharge profiles of test materials with various parameters (e.g.,

capacitance, inductance, and resistance). Systematic experiments looking at the discharge

characteristics of the spark will also help understand the way energy is dissipated in an

electrostatic discharge enabling a better understanding of the ignition characteristics of

materials in terms of energy and the dissipation of that energy in an electrostatic discharge.


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Table of Contents

1.0 Introduction .......................................................................................................................... 1

1.1 Introduction ...................................................................................................................... 1

1.2 Theory .............................................................................................................................. 3

1.3 Research Method ............................................................................................................. 4

1.3.1 High Voltage measurement....................................................................................... 6

1.3.2 Low Voltage Discharge Simulation and Measurement ............................................ 7

1.3.3 High Voltage Discharge Simulation and Measurement............................................ 7

1.3.4 Ignition Experiment .................................................................................................. 8

1.4 Application and Contributions ......................................................................................... 8

1.5 Conclusion ....................................................................................................................... 9

2.0 Literature Review............................................................................................................... 10

2.1 Introduction .................................................................................................................... 10

2.2 Electrostatics .................................................................................................................. 11

2.2.1 Charge transfer ........................................................................................................ 11

2.2.2 Conduction .............................................................................................................. 11

2.2.3 Induction ................................................................................................................. 11

2.2.4 Triboelectricity ........................................................................................................ 12

2.2.5 Electrostatics Summary .......................................................................................... 14

2.3 Human body model ........................................................................................................ 16

2.4 Charged Device Model .................................................................................................. 17

2.5 Machine Model .............................................................................................................. 18

2.6 Electrostatic Discharges as an Ignition Hazard ............................................................. 20

2.7 Discharge energy ........................................................................................................... 21

2.7.1 Capacitive Energy ................................................................................................... 23

2.7.2 Energy Dissipation .................................................................................................. 25

2.8 HV measurement ........................................................................................................... 26

2.8.1 Resistive Voltage Divider ....................................................................................... 26

2.8.2 Capacitor compensation .......................................................................................... 27

2.8.3 Oscilloscope ............................................................................................................ 29

2.8.4 Discussion/conclusion............................................................................................. 31

3.0 High Voltage Measurement Review .................................................................................. 32

3.1 High Resistance High Voltage-Voltage Divider............................................................ 32


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3.2 Frequency Response of Resistive Divider ..................................................................... 35

3.3 Equivalent Capacitor Voltage Divider ........................................................................... 37

3.3.1Resistor-Stray Capacitance Evaluation .................................................................... 39

3.3.2 High Voltage Capacitive Resistive Divider -Stray Capacitance Evaluation .......... 41

3.4 Oscilloscope Calibration ................................................................................................ 42

3.5 Current Measurement..................................................................................................... 44

3.6 Discharge Resistor High frequency Response ................................................................... 46

3.7 Measurement Errors and Absolute Errors ...................................................................... 47

3.8 Conclusion ..................................................................................................................... 48

4.0 Low Voltage Discharge Simulation and Measurement ..................................................... 49

4.1 Low Voltage Discharge Simulation and Measurement Experiment Method ................ 50

4.2 Low Voltage Discharge Simulation and Measurement Experiment Results and

Analysis................................................................................................................................ 52

4.3 Low Voltage Discharge Simulation and Measurement Experiment Discussion ........... 54

4.4 Low Voltage Discharge simulation and Measurement Experiment Conclusion ........... 57

5.0 High Voltage Discharge Simulation and Measurement..................................................... 58

5.1 High Voltage Measurement Circuit ............................................................................... 59

5.1.1 High Voltage Measurement Circuit Simulations .................................................... 59

5.1.2 High Voltage Measurement Circuit Evaluation ...................................................... 64

5.1.3 High Voltage Measurement Circuit Oscilloscope Compensation .......................... 65

5.1.4 High Voltage Measurement Circuit Overview ....................................................... 66

5.1.5 High Voltage Measurement Circuit Attenuation Calculation DC .......................... 72

5.1.6 High Voltage Measurement Circuit Attenuation Calculation High Frequency ...... 73

5.1.7 High Voltage Measurement Circuit Absolute Errors.............................................. 74

5.1.8 High Voltage Simulation ........................................................................................ 75

5.2 High Voltage discharge Experimental Method .............................................................. 77

5.2.1 High Voltage Experiment Circuit ........................................................................... 77

5.2.2 Experiment procedure ............................................................................................. 80

5.2.3 Energy Calculation.................................................................................................. 80

5.3 Results and Analysis ...................................................................................................... 81

5.3.1 Discharge Current and Voltage Waveforms ........................................................... 81

5.3.2 Experiment Calculations and Results ..................................................................... 85

5.3.3 Discharge Voltage ................................................................................................... 85


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5.3.4 Energy in the Capacitor .......................................................................................... 89

5.3.5 Discharge Resistor Energy Dissipation .................................................................. 90

5.3.6 Discharge Point Energy Dissipation ....................................................................... 91

5.3.7 Unaccounted Energy Results Summary .................................................................. 93

5.3.8 Peak Current............................................................................................................ 93

5.4 Discussion ...................................................................................................................... 95

5.4.1 Discharge Current and Voltage Waveform Discussion .......................................... 95

5.4.2 Results Summary-Discussion ................................................................................. 97

5.4.3Discharge Voltage-Discussion ................................................................................. 97

5.4.4 Capacitor Energy-Discussion.................................................................................. 97

5.4.5 Discharge Resistor Energy Dissipation-Discussion................................................ 97

5.4.6 Discharge Point Energy-Discussion ....................................................................... 98

5.4.7 Unaccounted Energy-Discussion ............................................................................ 98

5.4.8 Peak Current-Discussion ......................................................................................... 99

5.5 High Voltage Discharge Simulation and Measurement- Conclusion ............................ 99

6.0 Materials Ignitions ........................................................................................................... 100

6.1 Introduction .................................................................................................................. 100

6.2 Method ......................................................................................................................... 101

6.3 Results and Analysis .................................................................................................... 102

6.3.1 Ignition Energy and Minimum Ignition Energy ................................................... 102

6.3.2 Ignition Probability Statistical Analysis ............................................................... 102

6.3.3 Ignition Discharge characteristics ......................................................................... 106

6.4 Material Ignition Discussion ........................................................................................ 107

6.4.1 Minimum Ignition Energy .................................................................................... 107

6.4.2 Ignition Probability ............................................................................................... 107

6.4.3 Ignition Discharge ................................................................................................. 108

6.4.4 Capacitance vs. Discharge Energy ........................................................................ 108

6.5 Material Ignition Conclusion ....................................................................................... 108

7.0 Contributions and Conclusions ........................................................................................ 110

7.1 High Voltage Measurement ......................................................................................... 110

7.2 Low Voltage Experiment ............................................................................................. 111

7.3 High Voltage Experiment ............................................................................................ 112

7.4 Material Ignition Experiment ....................................................................................... 114


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7.5 Conclusions .................................................................................................................. 115

8.0 Future Work ..................................................................................................................... 117

9.0 References ........................................................................................................................ 118

10.0 Appendix ........................................................................................................................ 122


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List of Figures

Figure 2.2.1.1 Charge Transfer Conduction. ........................................................................... 11

Figure 2.2.1.2 Charge Transfer Induction. ............................................................................... 12

Figure 2.2.2.3Charge Transfer Triboelectricity. ...................................................................... 13

Figure 2.4.0.1CDM Current Waveform ................................................................................... 18

Figure 2.5.0.1 MM Current Waveform .................................................................................... 19

Figure 2.8.1.1 Resistor Voltage Divider .................................................................................. 27

Figure 2.8.2.1 Capacitor Coupled Voltage Divider. ................................................................ 28

Figure 2.8.3.1 Oscilloscope Schematic .................................................................................... 30

Figure 3.1.0.1 High Voltage Resistive Divider........................................................................ 35

Figure 3.2.0.1 1GΩ Frequency Response of Resistive divider in Linear Magnitude Ω .......... 36

Figure 3.3.0.1High Voltage Capacitive Resistive Divider ...................................................... 39

Figure 3.3.1.1 Plot of 1GΩ Stray Capacitance Over Frequency ............................................. 40

Figure 3.3.2.1 Plot of Coupled 2GΩ/1pF Capacitance over Frequency .................................. 41

Figure 3.4.0.1 Schematic of 1X Probe and Oscilloscope ........................................................ 43

Figure 3.4.0.2 Schematic of 10X Probe and Oscilloscope ...................................................... 43

Figure 3.5.0.1 Plot of 0.1Ω Current Measurement Section over Frequency ........................... 45

Figure 3.6.0.1 Plot of 1.5 kΩ Discharge Resistor over Frequency .......................................... 47

Figure 4.1.0.1 Schematic of the low voltage ESD simulation experiment .............................. 51

Figure 5.1.1.1 Initial High Voltage Divider ............................................................................. 61

Figure 5.1.1.3 Simulated Frequency Response for the Divider at 2MΩ Node ........................ 63

Figure 5.1.2.1 Coupled High Voltage Divider ......................................................................... 65

Figure 5.1.3.1 Compensated 2X Probe Oscilloscope Equivalent Circuit ................................ 66

Figure 5.1.4.1 Complete High Voltage Measurement Circuit ................................................. 68

Figure 5.1.4.2 Complete High Voltage Measurement Equivalent Circuit 1 ............................ 69





Figure 5.2.1.1 Overall Experiment Circuit .............................................................................. 79

Figure 5.3.1.1 Experiment Results- Discharge Voltage Waveform at Discharge Capacitor ... 83

Figure 5.3.1.2 Experiment Results- Discharge Current Waveform ......................................... 84

Figure 5.3.3.1 Plot of Discharge Voltage Results with absolute error .................................... 86


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Figure 5.3.4.1 Plot of Initial Capacitive Energy with absolute error ....................................... 89

Figure 5.3.5.1 Plot of Discharge Resistor Energy Dissipation with absolute error ................. 91

Figure 5.3.6.1 Plot of Discharge Point Energy Dissipation with absolute error ...................... 92

Figure 5.3.8.1 Plot of Peak Current with absolute error .......................................................... 94

Figure 6.3.2.1 Plot of Ignition Results and Ignition Probability Curve for N-Pentane ......... 106

Appendix 10.2 Plot of 500MΩ Frequency Response in Linear Magnitude Ω ...................... 123

Appendix 10.3 Plot of 200MΩ Frequency Response in Linear Magnitude Ω ...................... 123

Appendix 10.4 Plot of 500MΩ Stray Capacitance over Frequency ...................................... 124

Appendix 10.5 Plot of 200MΩ Stray Capacitance over Frequency ...................................... 124

Appendix 10.6 Plot of 200MΩ/10pF Capacitance over Frequency ...................................... 125

Appendix 10.7 Plot of 2MΩ/220pF Capacitance over Frequency ........................................ 125

Appendix 10.10 High Voltage Experiment Setup ................................................................. 153

Appendix 10.11 High Voltage Experiment Discharge Point ................................................. 154

Appendix 10.12 High Voltage Experiment Measurement Equipment .................................. 155

Appendix 10.13 Ignition Experiment, Ignition Frame Extract from High Speed Camera .... 156


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List of Tables

Table 3.3.1.0.1 Table of Stray Capacitance Results ................................................................ 40

Table 3.3.2.0.1 Table of Evaluated Capacitance Results ......................................................... 42

Table 4.1.0.0.1 Table of experimental variables matrix for the low voltage ESD simulation 51

Table 5.1.2.0.5 Table of High Voltage Divider-Stray Capacitance Results ............................ 65

Table 5.1.7.0.1 Resistive Measurement Error .......................................................................... 74

Table 5.1.7.0.2 Capacitive Measurement Error ....................................................................... 75

Table 5.3.2.0.1 Experiment Results-Summary of Discharge Energy Results for 100pF

simulation and experiment ....................................................................................................... 87

Table 5.3.6.1.1 Discharge Point Energy Dissipation Results .................................................. 93

Table 5.3.2.0.1 Unaccounted Energy Result Summary ........................................................... 93

Table 5.3.8.1.1 Peak current summary .................................................................................... 95

Table 6.3.0.0.1 Ignition and No Ignition Discharge Result Summary .................................. 103

Appendix 10.1 Table of Triboelectric Series ......................................................................... 122

Appendix 10.9 Simulation and Measurement of an Electrostatic Discharge Low Voltage

Experiment Results ................................................................................................................ 139

Appendix 10.14 Table of Ignition and No Ignition Results................................................... 160

Appendix 10.15 Data for Ignition Probability Plot, with Ignition Data ................................ 162


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Nomenclature

A Amperes

C Coulombs

Cm3 centi-Meter cubed

GΩ Giga-Ohm

GHz Giga-Hertz

kHz kilo-Hertz

kΩ kilo-Ohm

kV kilo-Volt

mA milli-Amperes

MHz Mega-Hertz

mJ milli-Joules

mm milli-Meter

mΩ milli-Ohm

nF nano-Farad

nH nano-Henry

nS nano-Second

pF pico-Farad

pS pico-Second

V Volt

W Watts


XVI

Eqn 1 Spark Energy Estimation Es = Ec − Er − Eresidual,

Eqn. 2 Coulomb’s Law

= 124 ∙

Eqn 3 Force

=

Eqn 4 Field Strength

=

Eqn 5 Field Strength

= 4 ∙

Eqn 6 Net Flux

Φ = ∙ = ∙ ! =

Eqn 7 Field strength for parallel plates

= "

Eqn 8 Voltage potential

# = $ , $ = # = ∮ ∙ & ∙ '

Eqn 9 Energy/work

( = 12 $ ∙ #, # = 1$ ) ∙ *

Eqn 10 Attenuation of resistor voltage divider


XVII

+ = ,1 + ,2,2

Eqn 11 Attenuation of capacitor coupled voltage divider

+ = $1 + $2$1

Eqn 12 Attenuation of coupled voltage divider

+ =,11 + ./,1$1 + ,21 + ./,2$2,21 + ./,2$2

Eqn 13 Attenuation ratio ,1,2 = $2$1

Eqn 14 Cut off frequency

01 = 12 ∙ ∙ , ∙ $

Eqn 15 Capacitance Reactance Equation

21 = 12 ∙ ∙ 0 ∙ $

Eqn 16 Capacitance-frequency and –j dependant

$ = −.2 ∙ ∙ 21 ∙ 0

Eqn17 Absolute Error

3456'7*8 6 = ± 12 :;<;=7= =8+578+4'8 >+'78

Eqn 18 Measurement Relative Error

,8'+*;>8 6% = ±+456'7*8 86=8+578 >+'78 × 100%

Eqn 19 Energy dissipated in resistor


XVIII

( = #, ∙ *

Eqn 20 Energy dissipated at the discharge point

( = (#1 − #) ∙ #, ∙ *

Eqn 21 unaccounted energy

(7<+1167<*8 = (1+D+1;*6 − (85;5*6 − (;51ℎ+F8

(7<+1167<*8 = 12 $ ∙ # − #, ∙ * − (#1 − #) ∙ #, ∙ *

Eqn 22 Ohm’s Law

# = ) ∙ ,, ) = #,

Eqn 23Natural Frequency RLC Circuit

/G = 1√I ∙ $ , /J = 2K

Eqn 24 Damping Factor RLC Circuit

L = ,2 M$I

Eqn 25 Logistic Regress Modelling Probability of Ignition/No Ignition

N = 8(OPQOR)(1 + 8OPQOR)


XIX

Definitions and Abbreviations

Charged Device Model (CDM)

Charge device model is a specified equivalent circuit that characterises a

device that is charged, and then discharges to ground or another object of less

or opposite charge.

Electrostatics (ES)

The study of static electrical charges & its effects and transfer (conduction,

induction or discharge).

Human Body Model (HBM)

Human body model is an equivalent circuit model of the human body, in terms

of resistance, capacitance and inductance.

Machine model (MM)

Machine model refers to an equivalent circuit where instead of the human

body to be the main item of interest, a particular machine is modelled.

Minimum Ignition Energy (MIE):

The minimal amount of energy required to ignite a particular material or

object in a particular environment. Ignition does not necessary imply

continuous combustion, propagation, or explosion.

Static Electricity (SE)

Similar meaning to Electrostatics. Adopted before Faraday demonstrated that

electricity is in the form of movement of positive and negative charges, and

static electricity is where electrons are stationary.

Stray Capacitance

Stray Capacitance in this document refers to the additional unexpected

capacitance that exhibits at high frequency. This is common as surface

capacitance across large resistances as the insulation exhibits parasitic

capacitance effects to ground at high frequency.

Stray Inductance

Stray Inductance refers to the additional unexpected inductance due to

manufacture/design of the components. Inductance is apparent at high

frequency and its effects can be seen as oscillatory ringing signals. This


XX

inductance derives from internal construction and conduction path within the

component. E.g. looping conductive paths.


1.0 Introduction

1

1.0 Introduction

1.1 Introduction

Electrostatic discharges have been identified as one of the most likely cause in a number

of incidents of fire and explosions with unexplained ignitions [1-3]. The lack of data and

suitable models forms a void in the analysis to quantify the significances of static

electricity in these situations. Emphasis must be placed on the fact that electrostatic

charge build up is a natural phenomenon that will occur with any situation of charge

transfer. It is not limited to human interactions with our physical world. In industrial

scenarios, repetitive actions cause cyclic transfers of very small amounts of charge. A

charge build-up creates a significant combustion hazard that can lead to catastrophic

damage, destroy plants and cause harm to personnel.

Quantifiable hazard analysis of the risk of ignition by static discharge cannot be entirely

carried out with our current understanding and experimental results. Improved

experimental models need to be established using a systematic procedure in order to

characterise the energy associated with electrostatic discharge.

The study of electrostatics and the associated fundamental principles have been around

for a long time. However it was not until the wide spread application of electronics that

research was developed for the protection of these electronics from electrostatic

discharges. The ever increasing amount of newly created technology drives new research

to develop methods and experiments to assess the hazardousness of electrostatics to

materials. Currently, experimental models for electrostatic discharge developed for

intrinsic safety with electronics are inadequate for ignition analysis. As interest increased

in the area of hazardousness electrostatic discharge, research continues with the models

established for electronic safety testing.

Previous work presented in the Confirmation Document in Appendix 10.16 showed in

agreement with related work that a resistive characteristic could be drawn to characterise

the energy dissipation of the discharge [4-6]. This research entailed examining the voltage


1.0 Introduction

2

and current characteristic of the discharge, and a complete discharge characteristic for a

Human Body Model was created. From the initial simulation and experiments, it was seen

that discharge energy represents about 10% of the initial capacitive energy and that the

energy dissipation was within 10ns of the initial discharge, where potential breaks down

and current flows through the arc in the discharge [6]. This is expected considering the

discharge characteristic of voltage and current in relation to the energy dissipation. As the

initial break down occurs the potential difference is the greatest, allowing the majority of

the energy to be dissipated. The discharge arc is then established and minimal energy is

dissipated as energy dissipation becomes greatly influenced by other components and

stray resistance in the discharge circuit. From the initial work of low voltage simulations,

the importance of the energy dissipation and the characteristic of the discharge is

emphasised, as the discharge energy would be as high as 30-40% of the capacitive energy

in an actual resistor/capacitor discharge and the characteristics of the discharge will

determines the energy dissipation over the discharge period [6].

High voltage simulation and experimentation of the electrostatic discharge required an

accurate measurement setup in order to achieve the precise measurement of the energy

dissipation. Building on the model of electrostatic discharge from electronic intrinsic

safety, the human body model was used as a basis to simulate electronically the discharge

characteristics. Expanding on the results and understanding of energy dissipation in

preliminary work, energy dissipation of the discharge in comparison to the total initial

capacitive energy was investigated. Voltage and current measurement were recorded on

strategic positions on the discharge circuit, allowing the discharge characteristic to be

recorded and energy dissipation in the discharge circuit analysed. Discharge energy

calculation shows consistency from low voltage work with discharge energy representing

about 40% of the total initial capacitive energy.

Research shows that ignition energy needs to be investigated on a more complex system

in order to achieve an accurate quotation of the minimum ignition energy [4, 6]. However,

the more complex the discharge system becomes; the more difficult it is to achieve

precision in energy calculation. Effects of the measurement circuit plus any possible stray

capacitance, inductance and resistance need to be taken into account, as they greatly

impact on the energy dissipation.


1.0 Introduction

3

High voltage ignition energy measurements were conducted on ignitions of n-Pentane

solution evaporated in a 250cm3 chamber. A series of ignition experiments was conducted

to determine the minimum ignition energy of n-Pentane. The lowest recorded ignition

energy was 0.352 mJ, with statistically results showing P=0.1 E=0.269 mJ, P=0.5

E=0.448 mJ and P=0.9 E=0.627 mJ. From the results, the importance of circuit

configuration on the discharge characteristic and ultimately the ignition energy can be

inferred.

Through this research, energy dissipation was found to be based heavily on the circuit

configuration of capacitance and resistance. Varying the capacitance varies the initial

energy plus the duration of discharge. Initial experiments showed that varying of

resistance varies the peak current and the duration of discharge. The analysis established a

discharge profile for the discharge that caused ignition for this set of experiments. This

methodology provides a base for further research into different materials and atmospheres,

by systematically looking at discharge profiles of test materials with various parameters

(e.g., capacitance, inductance, and resistance).

Systematic experiments looking at the discharge characteristics of the spark will help

understand the energy dissipation of the electrostatic discharge. This will allow us to

understand the ignition requirements in terms of energy and the dissipation of that energy

in an electrostatic discharge.

1.2 Theory

Static electricity is the build-up of static charges and presents an electrostatic hazard in

the potential unwanted release of energy [1]. This energy is built up by the transfer of

charges as described by the theories of conduction, induction and triboelectricity of

electrostatics. The release of this energy either to ground or an oppositely charged object

is what causes hazards. In most cases, the release of charges is undesired, unwanted and

unintentional. The usual form of release or dissipation of static electricity is in the form of

an electrical arc, which has the potential to lead to an ignition and consequently

combustion or explosion of nearby material/fuel.


1.0 Introduction

4

Electrostatic build up and discharge has been categorised into models representing their

use and characteristic. Most widely known, is the Human Body Model (HBM), which is

simulated by capacitor and resistor[7]. It is the most common test model for electronics

protection, as human interaction is the most common form of damage to electronic

components whether in production or application. The human body is reduced down to an

equivalent electronic circuit of series connected resistor and capacitor, with R 1.5 KΩ and

C 100 pF [7].

Energy in the discharge has not been the main aspect in the previous studies for electronic

component testing. Recent research on discharge energy is related to electronics and uses

models developed for discharge energy consideration. A wholly discharged capacitive

energy is the approach taken where the total capacitive energy is the discharge energy,

with considerations to residual capacitive energy.

Measurement of high voltage discharge requires a complex design of circuits to allow

safe and accurate recording of voltages and currents. To achieve this, an extensive study

was conducted for the measurement of high voltages and extremely fast discharges. In

order to measure such a high voltage discharge, specially designed voltage dividers were

needed to step down the discharge voltage. However the voltage not only needs to step

down, it also needs to be matched capacitively to ensure correct ratio is retained.

Competency and understanding of the measurement equipment is required to ensure

recorded data is accurate. Accurate measurement will allow energy dissipation to be

calculated and an understanding of how the discharge energy compares to the initial

capacitive energy and the resistive dissipated energy.

1.3 Research Method

Through literature review, the advantages and disadvantages for each of the standardised

model for electrostatic simulation was determined. The models are Charged Device

Model (CDM), Human Body Model (HBM) and Machine Model (MM). These models

were first established as an electrical representation of what the expected discharge and

damage would be if discharged from the various possible scenarios. As the intended uses

of these models were to test intrinsic safety of electronic components; the major

difference in regard to investigate is the utilising of the model for energy calculation. The


1.0 Introduction

5

Charged Device Model (CDM) is based on the possible storage of charges and discharges

by an insulator on to an electronic component [8]. It is a pure capacitive representation

with no additional resistance or inductance. From literature, a Charged Device Modelled

discharge tends to have high peak current and extremely short time frames [8-10].

A Human Body Model (HBM) is derived from the simulation of the human body as

electrical component in order to observe the effects of discharges from a human to an

electronic component [7]. The human body from an electrical equivalent point of view is

composed of resistance and capacitance with minimal inductance. The values are quoted

to be 1.5k Ω and 100 pF for a standard body. From past work, discharge from a Human

Body Model tends to have a longer discharge time compared to Charged Device Model

and a lower peak current due to the resistance.

Machine Model (MM) came about from the possible storage of charges and discharges in

repetitive action on a mechanized system [11]. Due to the open ended-ness of application,

the only defining aspect is that discharges are calibrated through a 500 Ω resistor. There

is no limit for capacitance since possible charge storage is dependent on the system. For

general testing, the recommended value is 200 pF. With a resistive component, the peak

current is expected to be similar to the Human Body Model and with discharge time

frame to be dependent on the capacitance

Research on electrostatic discharge is limited as we lack sufficient understanding of the

phenomenon, in particular the dissipation of energy involved and the effects on ignition

by the equivalent electrical components. Electrostatics as a hazard has only gained focus

in the last 10 years, mainly due to the need for further understanding of unexplained

ignitions in various accidents. This created the need to understand the energy dissipation

of the discharge in order to comprehend the ignition probability. The models established

for electronics intrinsic safety provides a basis for further research into the energy aspect

of an electrostatic discharge. The Human Body Model is investigated in detail in this

study with ignition energy experimentations, as Human Body Model, represent the most

widely spread of the hazards with the addition of resistive component allowing greater

control over discharge.


1.0 Introduction

6

Through the literature, we have seen an increase in complexity in the measurement and

calculation of discharge energy [12-14]. From the rough estimation of total initial energy

in the capacitor as adopted in various standards to a more precise estimation of discharge

energy by measuring current and discounting the energy lost by other know components

in the discharge circuit. This research looks at the energy in the discharge by measuring

voltage and current of the discharge, in order to create a discharge profile.

Ignition energy needs to be investigated on a more complex system in order to achieve an

accurate quotation of the minimum ignition energy. However, the more complex the

discharge system becomes; the more difficult it is to achieve a precision energy

calculation. The effects of the measurement circuit plus any possible stray capacitance,

inductance and resistance impact greatly on the energy dissipation.

1.3.1 High Voltage measurement

In order to measure directly the high voltage at discharge, a specifically designed voltage

divider bridge is required. The bridge will need high voltage rated components with

compensation capacitors in order to maintain attenuation over the discharge event. This is

due to the impulse response of the discharge requiring the voltage divider bridge to have

response from DC to 1+ GHz. To maintain the DC response, the divider needs to be

compensated and all known components included in the compensation.

Investigation found that large resistances have a reduced effect at high frequencies and

will exhibit unwanted characteristics, unless these effects are taken into account. High

frequency from the discharge will induce stray inductance and capacitance, which

introduces ringing oscillations into the discharge and significantly alters the overall

experiment circuit characteristics.

High frequency characteristic analysis found that mega ohm resistors have reduced

resistance and have additional capacitance and inductance. These effects were limited

through a component selection process for a high voltage measurement circuit, via

selection by manufacturing method/type and quality of construction. However, the stray

capacitance and inductance were still present when examined with a network analyser

creating a complex impedance profile of the components. These stray values are not only


1.0 Introduction

7

present in the high resistance components, but also in the cables, connections,

oscilloscope and probes. The only viable solution is to account for them in a final analysis

of the measurement circuit as an overall measurement circuit characteristic.

1.3.2 Low Voltage Discharge Simulation and Measurement

A simple experiment involving lower voltage was setup to simulate and measure an ESD

at low voltages with the aim to see the energy dissipation throughout the circuit.

Simulations of electrostatic discharges specified by IEC standards [7], set parameter such

as rise time, discharge period and discharge current. This is typically based on the

residual voltage/charge on the discharge capacitor, whereas this research examines the

voltage and current in the actual spark in order to obtain a more precise comparative

measurement of the energy dissipated. This allows us to better understand the energies in

the discharge.

Results from the low voltage experiment showed a hypothesis for energy calculation with

80-90% discharge resistor energy dissipation recorded, along with 5-15% energy

dissipation by stray resistances and 5-10% by the discharge point. This experiment has

shown the significance of stray resistance in the energy dissipation. The energy

dissipation in a discharge is dissipated through all the resistances in the circuit, including

resistors, stray resistances and breakdown potential. Leading to the conclusion that energy

dissipation in a discharge is dynamic and is mainly dissipated at the initial discharge

through any resistance as a factor of the peak current.

1.3.3 High Voltage Discharge Simulation and Measurement

From the previous low voltage investigation and experiment, a high voltage discharge

experiment and measurement circuit was designed, constructed and characterised for

calibration. Measurement circuit was simulated and analysed with respect to impedances

at high frequency, to allow characteristic to be defined for energy dissipation calculation.

Attenuated voltage is recorded and processed for calculation and analysis. Energy

calculation is done using the recorded voltage and current, to obtain at initial capacitive

energy, discharge resistor energy and discharge point energy.


1.0 Introduction

8

The results showed an overview of the high voltage discharge, with specific detail to

discharge voltage, initial capacitive energy, discharge resistor energy, discharge energy

and peak current. The experiment presents a functional method for investigating the

energy dissipation in high voltage discharges and ignition energy of materials relevant to

electrostatic discharge.

1.3.4 Ignition Experiment

Utilising the experiment methodology for ignition energy calculation from previous

investigation with high voltage discharge measurement, systematic experiments were

conducted to determine the minimum ignition energy of n-Pentane.

A minimum ignition energy and probability of ignition was obtained from the ignition

experiments. Lowest recorded energy for successful ignition was 0.352 mJ, with

statistical result of 0.269 mJ for 1% probability of ignition. Comparison to related work

show close agreement to ignition results.

1.4 Application and Contributions

Investigations have identified the importance of characterisation of the measurement and

experiment circuit for discharge experiments. It is a requirement by recommendation of

this research to fully characterise the circuitry before experiment so analysis can be

conducted. Three main characteristic are required to be determined and they are, 1)

component and overall resistance at high frequency, 2) stray capacitance in the circuit and

3) impedance of cabling and current shunts used in analysis.

Low voltage experiment reiterated the importance of energy dissipation in the circuit as

the energy dissipated in the discharge would never be the initial capacitive energy since

components in the circuit and stray resistances will always dissipate a significant amount

of the energy.

An experiment methodology for measuring ignition energy in a high voltage discharge

was developed. The methodology allows the calculation of the energy dissipated

throughout the circuit and thus characterises the energy in the discharge. Characterisation


1.0 Introduction

9

done from the analysis of the data enables the particular properties of interest to be

defined and determined.

Utilizing the developed experimental system and methodology to calculate energy in the

discharge, the ignition characteristics of n-pentane have been explored. A minimum

ignition energy and probability of ignition was obtained from the ignition experiments

with comparison to related work show close agreement.

This application of consistent theory, validated through experiments that can be used to

identify hazards in the application domain, is fundamentally new due to the lack of

accurate data of electrostatics discharge (ESD) under the specific condition of hazardous

atmosphere and will thus contribute greatly to the scientific community. The significance

of this research will be use of the experiment system and experiment methodology to

determine ignition characteristic of materials. This allows the assessment of electrostatic

hazards in order to provide guidance for the avoidance of hazardous situations.

1.5 Conclusion

Investigations have identified key points of characterisation for the measurement of high

voltage discharge and have reinforced the importance of the distribution of energy

dissipation in an ignition energy calculation. Experimental methodology to calculate

ignition energy developed for this research has been successfully used to determine the

minimum ignition of n-Pentane as a validation.

This research and experimental work has provided a basis to assess electrostatic hazards

in a variety of situations not present in the current standards and safety practices. It brings

into focus the increased importance of hazardous atmosphere and material characteristics

in electrostatic hazard analysis. Therefore, it is essential that the experiment methodology

established and verified through a systematic procedure of experiments, contributing to

the current knowledge and standards for minimum ignition energy testing and

electrostatic discharge ignition testing.


2.0 Literature Review

10


2.1 Introduction

Electrostatic charge is the build-up of static electricity and an electrostatic hazard is the

potential unwanted release of that energy [15]. This energy is built up by the transfer of

charges as described by the theories of conduction, induction and triboelectricity of

electrostatics [16]. The build-up and discharge have been documented in various

standards and safety documents for the protection of electronics against damage by the

electrostatic discharge. Past research categorised the electrostatic discharges into three

main models with regards to their occurrence and electrical equivalence in an electrical

simulated circuit [7, 8, 11]. The three models are Charged Device Model (CDM), Human

Body Model (HBM), and Machine Model (MM). The release of this energy either to

ground or an oppositely charged object is what causes hazards, as in most cases this

discharge is unwanted and unintentional [15]. The usual form of release or dissipation of

static electricity is in the form of an electrical arc, which can lead to an ignition and

consequently combustion or explosion of flammable materials or fuels. This created the

need to understand the energy dissipation of the discharge in order comprehends the

ignition probability. The estimation of the total initial energy in the capacitor as adopted

in various standards is inadequate. This research will more precisely estimate the

discharge energy by measuring current and voltage while including energy lost by other

known components in the discharge circuit. Ignition energy needs to be investigated on a

more complex system in order to achieve an accurate estimation of the minimum ignition

energy. As the discharge system becomes more complex, the more difficult it is to

achieve a precise energy calculation. The effects of the measurement circuit plus any

possible stray capacitance, inductance and resistance greatly impact on the energy

dissipation. Measurement of electrostatic discharge requires a specifically designed

circuit with consideration of the high frequency response as the discharge occurs and the

ability to withstand the high voltage prior to and after discharge.



11

2.2 Electrostatics

2.2.1 Charge transfer

Conduction and electrostatic induction are important basic concepts in understanding

charge transfer in static electricity. This is also the case with triboelectricity, as it

describes the charge interaction when two objects are in contact and moved so that charge

from one object is transferred to the other object, leaving one object negatively charged

and the other positively charged [16]. This effect is dependent on the contact area, the

frequency of contact, the speed of movement, the material of the objects, and the

environment.

2.2.2 Conduction

Conduction is the transfer of charges when a charged object is brought into contact with a

neutral or oppositely charged object or the ground[16]. Conduction is shown below in

Figure 2.2.1.1, where a charge object is used to conductively charge a neutral object.

(A) (B) (C)

Figure 2.2.1.1 Charge Transfer Conduction.

The above illustration shows an example of conduction. A shows a

negatively charged object and a neutral object separated from each

other. B depicts the situation where the charged object is brought into

contact with the neutral object. The difference in charge is neutralized.

C depicts when the objects are moved apart and both object become

slightly negatively charged.

2.2.3 Induction

Induction is similar except no contact is made [16]. An example is when a charged object

placed next to a grounded object. If the ground link is broken and the charged object is

removed, the originally grounded object will now be charged oppositely to the original

+- -+- -+- -

+- +- -+- -+-

+- -+- -+- -

+- +- -+- -+-

+-+-+-+-+-

+-+-+-+-+-

- - - - - - - - -

- - - - - - - - -

+- -+- -+- -

+- +- -+- -+-

+- -+- -+- -

+- +- -+- -+-



12

charged object. This is shown in Figure 2.2.1.2, where a negative charged object in

brought into close proximity of the grounded object, then the ground link is severed while

the charged object is removed, leaving the grounded object positively charged.

(A) (B) (C)

Figure 2.2.1.2 Charge Transfer Induction.

The above illustration shows an example of induction. A shows a

negatively charged object separated from a neutral grounded object.

The negative charged object is brought into close proximity, as shown

in B. The negative charged object then repels the negative charges in

the lower object to flow into the ground. As the ground is severed and

the two objects are separated, the originally grounded object becomes

positively charged as shown in C.

2.2.4 Triboelectricity

Triboelectricity is the theory of charge transfer due to of the contact of materials together

rubbing, brushing, or any other physical contact that allows charges to be stripped from

one object and stored on other [16]. These different materials form a conductive adhesion

when brought into contact and forms an electrochemical bond on the atomic level. When

the materials are separated, one material losses electrons and is left with a positive charge

and the other material gains the electrons and is left with an overall negative charge. As

shown in Figure 2.2.2.3, where two different material are rubbed or repetitive contact

resulting in electrons being striped by one material leaving one material negatively

charged and the other positively charged.

- -

+ + + + + +

+ + + + + +

- - - - - - - - -

- - - - - - - - -

+-+-+-+-+-

+-+-+-+-+-

- - - - - - - - -

- - - - - - - - -

+ + + + + +

+ + + + + +

- - - - - - - - -

- - - - - - - - -



13

(A) (B) (C)

Figure 2.2.2.3Charge Transfer Triboelectricity.

The illustration above demonstrates triboelectricity charge transfer.

The situation in A shows two neutral objects in contact. B illustrates

the rubbing and the creation of the negative charge build and the

positive charge build up on the opposing rubbing surfaces. As the

materials are separated, as shown in C, the surfaces maintain the

opposing oppositely charges.

The table of Triboelectric series is as shown in Appendix 11.1, and it presents the

material that are more likely to be positively charge on top and down to negatively

charged material. It can be seen from the table that it is the insulative material that are

more likely to be positively charge and the conductive materials to be negatively charged.

Therefore by bring into contact or rub.

There has been substantial work done in the past in relation to the chargeability of non-

metallic materials, in particular clothing [17-19]. The Textile Institute has series

publications called Textile Progress. In particular, Volume 28, Number 1 (Electrostatic

Charging of Textile) of this series, deals directly with the electrostatic charging of textile

material and methodologies to determine charge on the material [18]. The publication

covers extensively the properties of textiles and the characteristics to determine the

chargeability of them. There are other studies which explore the chargeability of non

metallic materials for the particular application in clean rooms to limit the electrostatic

build up in electronics manufacturing and handling [18, 20]. Other work explores at the

possibility of limiting electrostatic build up with additives in the materials to promote a

Negative series material

Positive series material

+ + + + + +

+-+-+-+-+-

+-+-+-+-+-

- - - - - - - - -

+-+-+-+-+-

+-+-+-+-+-

+-+-+-+-+-

+-+-+-+-+-

+ + + + + +

+-+-+-+-+-

+-+-+-+-+-

- - - - - - - - -

Rubbing



14

higher conductivity[21]. While work has been done on the contact electrification and

conduction in polymers, where an experiment of system was designed to place charges on

polymer fabrics by conduction [22]. Other than the above articles that deal specifically

with charging of non metallic materials, fundamental principles of triboelectricity are

covered in many extensive standards and guides to electrostatics [16, 23-25].

2.2.5 Electrostatics Summary

The principles of charging a non-metallic material are well known. However, there is a

need to calculate and measure the amount of charge capable of being deposited on a

material. This need is for the protection and prevention of electrostatic hazards, as the

minimum ignition energy (MIE) of materials can be formulated from the previous area.

Minimum ignition energy is not a property in electronic and triboelectricity investigation,

the collective investigation from theory to applied experiment in recent researches ties

together the MIE and hazardousness property to electrostatic discharge [11, 12, 26-28].

As an extended application of that focus the calculated MIE can be compared to the

measured MIE of the material, to determine whether the material could be an electrostatic

hazard in a simulated situation and then extend its application to real life scenarios. In a

real life scenario, many other variables will change the electrostatic build up and

ultimately the electrostatic discharge. These variables include humidity, air, elements in

the air, temperature, pressure, and materials involved in the contact charge transfer.

Past research has provided a wealth of information in the format of standards from

International and Australian standards on the topics of electrostatic control and

electrostatic protection. These are sources of electrostatic principles and general safe

practices; however they fail to address specific areas such as the increased effects of

oxidization on the ignition energy of the ignited material and the characterization of

materials in terms of electrostatic properties of chargeability, charge retention ability, and

the quantified energy for ignition.

Two Australian standards directly address this topic; namely AS/NZS 1020:1995 [23],

and AS/NZS 61000.4.2:2002 [29]. Standard AS 61000.4.2:2002 is a direct derivative of

IEC 61000-4-2 Ed 1.2B:2001 which covers the required protection and test methods for

electrical and electronic systems. The described test method uses a High Voltage Direct



15

Current power supply to charge a storage capacitor to discharge into a test system, testing

the tolerability of the system to ESD. Since the purpose of this standard is to test the

immunity of electrical and electronic systems to ESD, it does not consider the energy in

the discharge and relations of the ESD energy to possible ignitions. However, the test

method can be adapted to test the required ESD energy for ignition, testing for the

minimum ignition energy under the specific conditions of increased oxidization.

The standard AS/NZS 1020 addresses the control of undesirable static electricity and is

presented as a comprehensive guide to the control of undesired static electricity [23]. It

covers the basic principles of electrostatics from generation of static to control of static

electricity in solid objects, persons, liquid and etc. The standard also covered general

detection of electric potentials and basics of measurement equipment for measuring static

electricity. This standard provide an inclusive view on the topic of electrostatic control,

but it does not address specific issues such as effects of increasing oxidization,

quantifying energy for ignition in everyday materials and electrostatic characteristics of

those materials in terms of chargeability, charge retain ability and energy discharged.

NFPA 77: Recommended Practice on Static Electricity [25] is the most recognised

standard on the topic of electrostatic practices in relation to fire safety. It is a concise

standard covering a very broad field including fundamental theories, static safety

practices, and the evaluation of static hazards. However, as it is a guide to the practices

dealing with static electricity, it does not address specific issues such as effects of

increasing oxidization, quantifying energy for ignition in everyday materials and

electrostatic characteristics of those materials in terms of chargeability, charge retention

ability and energy discharged. The guide does provide valuable information in the

industrial sector, with charge accumulation and dissipation in liquid or semi liquid

transfers of products. There is also information on possible conduction, triboelectricity

charge transfers in industrial applications of moving parts and charge transfer between

vehicles/large objects and ground. As with the subsequent standards that referenced this

standard, such as the AS/NZS 1020, it overlooked the fields of increasing oxidization and

the quantifying characteristics of everyday materials, such as fabric and textiles. This

creates a void in the required knowledge in our abilities to assess hazards and provide

preventative measures.



16

Noteworthy British standards include BS7506-1 and BS7506-2, whereas Part 2 provides a

series of test methods to determine electrical and electrostatic characteristics, which is a

basis for further studies, experiments and adaptations to achieve applicable results [9, 24].

Similar to its counterparts in the Australian Standard (AS) and the International

Electrotechnical Commission (IEC), in regards to the information it provides and the

depth of understanding, the BS 7506 series of standards also overlooks the specific issues

referred to above.

Standards make awareness to the potential danger, but lacks in depth investigation

required for definitive analysis of ignition hazards from electrostatic discharge. Results of

more recent research and this work, present a gap in the implementation of experiment

data to application of knowledge to hazard prevention [4, 27]. Literature on electrostatic

discharge (section 2.6) and discharge energy (Section 2.7) will further explore the issue at

hand.

2.3 Human body model

IEC61340-3-1[7] Electrostatics- Part3-1 Methods for simulating electrostatic effects-

Human body model (HBM) electrostatic discharge test waveforms[7], provides a model

of simulating and experiment with ESD with regards to HBM model. The standard

provides a standardised method of testing solid state electronics in terms of testing for

immunity from ESD from human operations. It provides an excellent point of

investigation as it provided current waveforms as to the ESD, as well as a method for

measurement. Current measurement described is to apply consistence to a human body

model discharge, with which the test would be repeated for a Device Under Test (DUT).

Expected current waveform for a no load and 500 Ω load were presented in the standard.

Although limited in the data that is drawn from this method of current measure of ESD, is

nonetheless an important stepping-stone in the investigation.

The Human Body Model is the most applicable model to this research in regards to

ignition probability and hazards. The standardised HBM model provides a basis for

experimentation and the defined variables allows measurement to be better defined. As in

consideration the added complexity of the discharge circuit due to addition resistance



17

reduces the effect of the stray resistance to the energy dissipation, HBM represents the

best consideration for ignition as the most unpredictable element is human contact.

The general consensus in the knowledge provided by the standards mentioned above is

that fundamental and general preventative and protective measures need to be provided,

and forming a basis for further studies and experiments in specified areas. However the

yet to be explored areas of increasing effects of oxidization on the ignition energy and

materials, and characterisation materials in terms of electrostatics properties of

chargeability, charge retention ability and the quantified energy for ignition greatly

identifies the void in the required knowledge in order to conduct quantifiable analysis

with respect to the specified materials.

2.4 Charged Device Model

The Charged Device Model (CDM) is the standard in integrated circuits (IC) intrinsic

testing. It is defined by the fast transient response on the order of nanoseconds and high

current due to lack of resistance. It is a simulation of pure capacitive discharge of the

charge stored by triboelectricity through manufacturing and handling.

Capacitance values ≤300 pF are used in the standard CDM ESD testing. The IC device

subject to testing is tested through its pins with the charges in the capacitance ≤1 kV. For

IC intrinsic testing, the procedure is for the IC device to be discharge 6 times with 3

positive and 3 negative charges. The residual charge is drained away to ground by a

ground plan with 1MΩ resistance.

The standard JESD22 provides an established test method for CDM ESD testing [8]. This

test is similar to ANSI/ESDA STM5.3.1 and AEC-Q100-011 [[9, 30]. JESD22 is the test

method for the evaluation of all packaged semiconductor components, thin film circuits,

surface acoustic wave components, optic-electronic components, hybrid integrated

circuits, and multi-chip modules of any of the above types of components. The testing

discharge is specified by the conditions voltage 100-2000 V, with rise time less than 400

pS, and compliance to the CDM current waveform as given below as an extract from the

stand [8].



18

Figure 2.4.0.1CDM Current Waveform

Plot of a generic CDM current waveform denoting the rise time (Tr),

the 50% Ip undershoot (U-), the 25% Ip overshoot (U+), and the peak

current Ip ©JEDEC[8]

This model for ignition research utilises a less complex discharge circuit. The difference

of resistance in comparison to the HBM has a significant effect on the discharge

waveform and thus the energy dissipation. The absence of resistance unrestraint the

current flow and introduces stray resistances from cable, wires and circuit set up, that will

affect the energy dissipation as discharge occurs. Repeatability in testing with this model

would concern energy dissipation in the great uncertainty in the calculation of energy

dissipation due to the exact length of cable, exact thickness, and how cable actually lies

on the table. The energy calculation can be conducted with the assumption that the

measurement circuit will not impact greatly on the discharge circuit.

2.5 Machine Model

Machine Model is used to test electrical components that are prone to possible damage

from electrostatic build up and discharge in the production process. It simulates the

possible triboelectric effect of charge transfer onto a capacitive median for storage and



19

discharge with no resistive component. JESD22-A115C [11] provides a method for

testing with MM as with ANSI/ESDA STM5.2 [31] and AEC-Q100-003 [32].

Standard testing involves charging a capacitor up to 300 pF to voltages up to 400 V,

before switch discharging through the Device Under Test (DUT). Initially the discharge

needs to be calibrated with a 500 Ω resistor to give a underdamped oscillatory pulse as

shown in the extract from the stand as below in Figure 2.5.0.1 [11].

Figure 2.5.0.1 MM Current Waveform

Plot of a MM current waveform 500 Ω taken from an example

calibration where the peak current (Ipr) is shown in amperes and time

in nanoseconds ©JEDEC [11].

Similarly with the Charged Device model (CDM), the Machine model (MM) neglects the

energy aspect of the discharge. The focus of the test method is to test for intrinsic safety

for electronic component by simulation discharge of Triboelectric gained charges in an

experimental method. Energy is not considered and only peak current and current

waveforms are considered.



20

2.6 Electrostatic Discharges as an Ignition Hazard

Electrostatic discharge hazards are well documented with the majority of investigation

deriving from the engineering of electronics and the electronic manufacturing industry.

Electronics are easily damaged when exposed to an ESD; therefore there is a great

amount of literature on the prevention, elimination, and protection of ESD in electronic

design, manufacturing, and use [33-35]. However, the research herein focuses on

electrostatics as a cause of accidents like the work of Taillet et al. [36]. Taillet et al

studied at great detail to find the possible cause of 3 major accidents and concluded that

electrostatic hazards was the most probable cause in all 3 cases.

As with all forces, the fundamental understanding of electrostatics by Masuda et al. has

lead to great inventions and applications [37]. Electrostatics is currently used in

applications ranging from droplet control in inkjet printers, electrostatic precipitators to

remove pollution, to force discharges to create plasma chemical effect to remove toxic

waste. In agreement with Castel et al. agrees with Masuda that the applications of

electrostatics are numerous and evolving.

The study of electrostatic hazards has gained greater importance in research in the last 50

years, as we began to understand the potential and potency of ESD. Gibson et al.

identified the lack work that defines the incendivity of discharges from non-conductors

consisting of solids, powders, or liquids and has lead to vast research in this area [38].

There have been a number of studies of the ignition probability of an ESD that exhibit a

broad range of variables. Wilson et al. explains that ignition of natural gas depends on the

following three factors: (1) the fragmentation of the discharges into discrete sparks, (2)

the loss of energy to the body resistance, and (3) the quenching effect of the electrodes.

The view that the loss of energy to the body resistance is shared by Butterworth et al. in

works that studied the incendivity of electrical discharges between planar resistive

electrodes [39]. Butterworth et al. determined that a resistance of 100 MΩ dramatically

decreased the possibility of ignition. Other ignition variables identified by Bailey et al.

include humidity and the container properties in studies conducted in power silos. The

test silo facility was described in detail and results from the experiments showed the

electrostatic potential built up as the experimental material was poured into the silo.



21

Furthermore, there were numerous discharges as an earthing probe was inserted into the

silo. Although the discharges were not sufficient to ignite the material, they do have the

potential to ignite other materials such combustible fuel. Bailey’s article has shown that

there is a need to develop a procedure and system to determine the minimum ignition

energy (MIE) of particular materials under various environments and scenarios. This is

the focus of this research. There also is a greater need to develop this standard with

regards to ignition in saturated oxygen, pressurised oxygen, non metallic materials, and

unstable combustible atmospheres (inert conditions).

Substantial research has gone into investigating hazards arising from an ESD in an

environment where the MIE has been lowered. This arises from the amount of charge that

can be built up on materials and has lead to instances where ignition and combustion has

not previously occurred. This area examines a potential hazardous environment, where

the introduction of an additional fuel has lowered ignition energy. This is important in the

correlation to the work of Bailey et al. in the area of powders in silo as well as hazards in

dust, flammable gas conditions, flammable vapours, mist [40-42].

In regards to protection, Wilson et al researched the ignition of natural gas via spark

discharges from the human body where it was found that some ignitions are prevented by

increasing the resistance in the human body.

Electrostatic Discharge (ESD) as a hazard is a substantial claim; however a clear regime

has not been identified or established quantifying the hazardousness of ESD. The

understanding of the discharge energy and in particular the energy dissipated is

paramount in order to assess the ignition energy of materials and hazardousness. Thus

identify ESD as a hazard and ignition source under various conditions.

2.7 Discharge energy

The need to better understand the energy dissipated in the discharge has become apparent

with the limited research present in this particular area of Electrostatic Discharge (ESD).

The acknowledgement of the discharge profile, that is dependent on the discharge circuit

configuration, is paramount in the research to determine ignition energy. The

hazardousness of an ESD need to be quantified through the investigation of the discharge



22

energy. Through the investigation of discharge energy we can develop a model and

hypothesis for ignition probability of flammable material and fuels. This model can also

reflect the energy lost in other parts of the simulation and present an estimation of the

actual discharge energy. This discharge energy then can be used for development of the

MIE of particular materials with specific to atmosphere and environmental conditions.

There have been extensive publications on the calculation and experimental measurement

of minimum ignition energies [13, 43]. However, these experiments have only dealt with

gases and fuel, where parameters such as the composition of gases, temperature, pressure

and enthalpy of the gases are known. These parameters play a major role in the

determination of the MIE. Outside of this body of work, there is a large gap in the

knowledge for the determination of the minimum ignition energy of materials through

electrostatic discharges.

There are a number of references that explore the minimum ignition of materials and

protection and prevention codes of practices of ESD. These include standards explored in

Section 2.2.3, and they provide a general description on the principles of electrostatics,

and the preventative and protective actions.

Lower energy for ignition of materials from ESD was investigated. These include

ignitions in oxygen, fuel environment, and the combination of the two. From the many

minimum ignition experiments and projects, only a few target the presence of the addition

of oxygen and its effect on the minimum ignition energy. The groups of interest in this

field are predominantly within Aerospace organisation such as NASA and the medical

health industries where hyperbaric chambers are used [44]. Smith et al. presented results

for spacesuit materials that went under extensive testing for the possible ignition due to

arcing of electrical wiring within the spacesuit [45]. It was shown that for given current

and voltage settings, materials used in spacesuits could readily ignite in the abundance of

oxygen. Other published work presents the importance in the of amount of energy, and

provided improvement to the calculation of actual energy dissipated in the electrostatic

discharge [25, 43, 46, 47] .

The focus of NASA’s investigation was to determine if the spacesuit materials would

ignite from exposed wiring and electrical arcing at levels present within the spacesuit



23

without quantification of the MIE [45]. Unfortunately, this study did not address the

lowest possible energy under which the test material would ignite and the atmosphere.

The experiment was operated under the assumption that there is continuous discharge and

that the electrical system would continue to provide power for an extended period of time

until a definitive ignition or no ignition has been recorded.

Ono et al. discusses the minimum ignition energy of hydrogen air mixture [4]. This was

an important aspect of research as hydrogen requires only a hundredth of the minimum

ignition energy of hydrocarbons. It was concluded by Ono that the residual energy in the

capacitor was insignificant as compared to the calculation of the overall energy. This can

also be done for the discharge resistance, so that the energy equation becomes:

Es = Ec − Er − Eresidual, (Eq. 1)

Ec is the energy in the discharge capacitor, Er is the energy dissipated in the discharge

resistance, and Eresidual is the capacitor residual energy.

The increasing use of oxygen in our daily lives from industrial applications, medical

applications to individual activities have placed a focus on the specific topic of discharge

energy. Electrostatic build up in our bodies are correctly assumed not sufficient to ignite

material that one might come into contact with in everyday life. However, the presence of

abundant oxygen changes the ignition energy requirement and hence further study to

avoid incident of hazards and accidents is demanded.

2.7.1 Capacitive Energy

Fundamentals of electrostatics are based upon the interactions of subatomic particles

consisting of a proton, neutron, and electron. Protons have a positive charge, while

electrons have a negative charge. Neutrons are neutral and thus are not important here.

Charges are measured in coulombs, C, which is 1 Ampere Second (As), and is used to

express a single electron’s or proton’s charge as ±1.608e-19

C. As like charges repel and

unlike charges attract, the force of the attraction or repulsion is expressed by Coulomb’s

law,



24

= 124 ∙

(Eq. 2)

where permittivity is given by orεεε = , Q1 and Q2 are charge 1 and charge 2

respectively, and r is the distance between the two charges. The applicability of

Coulomb’s law is limited to point charges. For a charge that experiences a force over a

region, Coulomb’s law can be rearranged to give the field strength E,

=

(Eq. 3)

=

(Eq. 4)

and thus,

= 4 ∙

(Eq. 5)

Gauss’ law applies the concept of electric flux and the assumption that the net flux of the

electric field equals the charge inside a closed surface,

Φ = ∙ = ∙ ! =

(Eq. 6)

This is the general equation used to calculate effects of charges in a typical numerical

analysis. The application of this equation and the derivative of the equation allows for the

estimation of the potential energy via discharge at a particular voltage potential across

two objects.

As simple model of parallel plates, gives an expression for;

= "



25

(Eq. 7)

which can be applied to the equations ;

# = $ , $ = # = ∮ ∙ & ∙ '

(Eq. 8)

to find the capacitance of the parallel plate model. With a calculated capacitance and a

known voltage the energy stored can be calculated by:

( = 12 $ ∙ #, # = 1$ ) ∙ *

(Eq. 9)

2.7.2 Energy Dissipation

Energy dissipation calculations rely on accurately measure the energy in the discharge

and the form of discharge (electrostatic discharge). Electrostatic discharges are low

energy discharges due to the circumstances in which the energy is discharged and

dissipated. The HBM models the human body into electrical components of capacitance,

inductance and resistance. These electrical components define the waveform in which the

discharge occurs and how the energy dissipated. Due to the extremely small time constant

in the equivalent circuit because of the low capacitance, the duration of an electrostatic

discharge is estimated to be about 10 ns. As charges build up on an object, the

potential/voltage of the object rises until a breakdown occurs.

# = $

(Eq. 8)

This breakdown occurs due to the weakness in insulation in air or the environment in

which the object is in. The breakdown voltage in air is 33kv per cm, which refers to the

voltage at which an arc will spark over the gap. From Ohm’s law, by increasing the

resistance the current flows at discharge would decrease [39]. It was shown by

Butterworth et al. that by increasing the resistance to 100 MΩ, it was possible to avoid

ignition in a grain silo. A large resistor, in which discharge occurs through, would provide

a low current and also a large time constant in which the built up energy in the capacitor



26

is dissipated. This is consistent with the finding of Ono[4], where Ono. concluded that in

the case of an ESD in a mixture of hydrogen and air that larger resistance values requires

a higher initial voltage in order to have an ignition. The delivery of the stored energy is a

factor in the ignition process and in the numerical calculation of an electrostatic build up

and discharge.

2.8 HV measurement

Direct measurement of high voltage requires rated components in a resistive voltage

divider. The principle involved is discussed in detail in High Voltage Measurement

Techniques by Schwab [48]. The use of a pure resistive voltage divider bridge creates

uncertainty in the measurement when a discharged is involved. The impulse effect of the

discharge affects the resistive divider as a high frequency distortion which then affects the

ratio of the divider. In order to retain accurate measurement, both Schwab and Douglas

suggested capacitive compensation to resolve high frequency effects [48, 49]. Ideally, the

ratio of the resistive voltage divider is retained in the compensation of capacitors, thus

allowing the time constant in each of the Resistor/Capacitor (RC) to remain the same.

2.8.1 Resistive Voltage Divider

In order to directly measure high voltage, a resistor bridge can be built allowing an

overall rating of the bridge to match or exceed the expected measured voltage. Neglecting

stray inductances and capacitances, it is expected that the ratio of the measured section to

the overall bridge to remain consistence throughout the measurement, as shown in Figure

2.8.1.1 where R1 and R2 are in series.



27

Figure 2.8.1.1 Resistor Voltage Divider

Schematic voltage divider bridge with ratio of 1000:1 whereas resistor

1 (R1, 1,000 MΩ) and resistor 2 (R2, 1 MΩ) are in series.

The resistance of R1 is much greater than R2 in order to decrease the potential due to

resistance. The attenuation of the resistor divider is given by:

+ = ,1 + ,2,2

(Eq. 10)

Extremely large resistances are required in order to achieve step down voltage

measurement for the experimental voltage of 30kV.

2.8.2 Capacitor compensation

Due to the fast transient effect during an ESD, the large resistances used in the resistive

voltage divider bridge will exhibit an unexpected response as high frequency effects the

resistances. The resistors will exhibit stray capacitance and inductance phenomena at high

frequency. The phenomena are dependent on the design, construction, and quality of the



28

resistors and capacitor compensation is required to limit their effects. This can be

achieved by coupling additional capacitor to the resistor bridge as shown in Figure 2.8.2.1.

The attenuation at high frequency levels in DC can be derived from the resistor values.

While high frequency levels, the attenuation would become a capacitive division equation

with the large resistance exhibiting stray capacitances that are coupled to the larger

known values of capacitors 1 and 2 (C1, C2).

Figure 2.8.2.1 Capacitor Coupled Voltage Divider.

Schematic of a resistive voltage divider bridge with capacitors C1 and

C2 coupled to maintain the resistive ratio of 1000:1.

Thus the equation becomes;

+ = $1 + $2$1

(Eq. 11)

and then the equation from the frequency dependence becomes;



29

+ =,11 + ./,1$1 + ,21 + ./,2$2,21 + ./,2$2

(Eq. 12)

In the DC regime, only the resistive part of the bridge exhibits the steady state attenuation

of:

+ = ,1 + ,2,2

(Eq. 10)

Ideally R1, R2, C1 and C2 are selected to match the following equation in order avoid

overcompensation or under-compensation. The equation for the attenuation characteristic

is given by;

,1,2 = $2$1

(Eq. 13)

and in terms of the time constant characteristic is given by:

,1 ∙ $1 = ,2 ∙ $2

(Eq. 13)

The voltage divider bridge should maintain DC characteristics in the high frequency

domain thus allowing for accurate measurements to be made. The capacitor compensation,

the selection of capacitor and resistors to these ideal equations must be considered in the

design of the voltage divider bridge in order to accurately measure an ESD.

2.8.3 Oscilloscope

In order to achieve accurate measurements, the internal workings of an oscilloscope need

to be investigated. This must be done in order to compensate for the oscilloscope’s

interference in the measurement circuit. Figure 2.8.3.1 shows the internal arrangement of

components that make up the standard 12-16pF capacitance and 1MΩ resistance in a

standard oscilloscope.



30

Figure 2.8.3.1 Oscilloscope Schematic

Schematic of a typical Oscilloscope depicting the input signal and resistor in series to sum to 1 MΩ ©HAMEG [50]



31

The configuration suggests that the capacitor and resistor are in parallel to the input signal

and the resistors are in series that create 1MΩ and allowing further reduction of the signal

voltage.

The internal 1 MΩ resistance of the oscilloscope is to be taken into account in the design

of a voltage divider bridge in order to reduce the voltage and maintain correct resistive

ratio (for this assessment: 1,000:1). The additional capacitances from the oscilloscope

will accumulate thus contributing to overall capacitance to be compensated. These

capacitances include capacitance in the probe, internal capacitance and stray capacitances.

The effect of the addition of the oscilloscope should be maintained at 16 pF, thus limiting

the probe compensation to 16 pF for the 1,000:1 ratio.

2.8.4 Discussion/conclusion

The complexity of circuit required to compensate each addition measurement component

grows exponentially with the accuracy of measurement required. Each component needs

to be characterised with respect to stray capacitance, inductance and frequency response.

Then the overall characteristic needs to be assessed with consideration of each individual

component. Full analysis is in the following Chapter 3 (High Voltage Measurement),

where component are assessed in regards to high frequency characteristics.


3.0 High Voltage Measurement Review

32


Through preliminary experiments and literature, it was concluded that high voltage

discharge measurement is a challenge at best. Various effects from the fast response of

the discharge combined with the high potential at discharge make accurate measurement

difficult. From NFPA 77 [25] electrostatic build up can achieve hundreds of thousands of

volts with breakdowns/discharges occurring as voltage reaches ~30 kV per cm in air. Due

to this high voltage, measurement requires a specialised circuit, in which voltage recorded

become a fraction of the voltage measured. A simple resistive voltage divider with high

voltage components stepping down the voltage would be sufficient to measure the high

voltage at discharge. However, the transient effects of the discharge alter the expected

response of a resistive divider, and would require complex circuitry and modelling to

accurately derive the expected response. Thus a review of component and circuit to be

used in a high voltage experiment and measurement need to be review and analysed for

their effects at discharge.

3.1 High Resistance High Voltage-Voltage Divider

High voltage measurement requires specialised equipment in order to obtain an accurate

measurement. High voltage components are required to achieve this. Previous work by

Ryo Ono[4], describes the use of a high voltage high resistance voltage divider bridge to

measure the steady state voltage of the charging circuit. The voltage divider used a high

voltage high resistance resistor of 1 GΩs in series with a 110 kΩ resistor to achieve a step

down voltage reading of 10,000:1 of the actual voltage. At this ratio, the voltage recorded

would be in the vicinity of 1-3 V if the breakdown voltage was 10-30 kV. This means that

measurements are more difficult at low voltage values. The large ratio will minimise the

actual voltage to the point where a reading is not distinguishable from the background

noise. Adopting the principle used to measure high voltage, the ratio was lowered to

allowing comparable testing at lower voltages. Lowering the ratio not only benefits in the

scaling data collected, but also allows easier differentiation of signal to noise. The ideal

ratio is 1,000:1, where expected input of to the oscilloscope is then 0-30 V from 0-30 kV.



33

There are a number of methods to construct the high resistance voltage divider, where the

main difference is the type of resistor used. The main types of resistors are Carbon

Composite, Wire-wound and Film [51]. The required criteria for the High Voltage High

Resistance Bridge are voltage rating up to 30 kV and resistances able provide to ratio up

to 1,000:1. To achieve this either a large number of lower rated component can be used in

series to provide the required rating or the preferred one or two components to provide

the rating and the voltage division. This is due to the fact that connections from 100 or so

component will become significant and induce possible stray capacitance and inductance

to the measurement circuitry. It is possible to compensate for the stray capacitance but it

is ideal to limit when appropriate. Stray inductance is to be avoided as inductance will

induce an oscillatory ringing effect which will require addition resistance to damp out,

adding further unnecessary complication to the measurement circuit.

Carbon composite resistors are made from carbon and ceramic dust moulded into solids

with the ratio of carbon to ceramic determining the resistance [51]. The quality of

manufacture will determine the stray capacitance and inductance. This method of

manufacture possesses the best possible method in limiting stray capacitance and

inductance. This is due to the presumed consistency in the resistance through the

component and because it’s made to a single conductive object with a simple path for

current flow. The limiting factor is the resistance and voltage rating achievable through

current technology in carbon composition manufacture[52]. Mega-ohm resistance in Kilo-

volt rating in carbon composite resistor are not possible or not readily available.

Wire wound resistors are constructed from conductors/wires wound on a solid insulator

usually in a spiral helix form [51]. Wire wound resistor provides the highest wattage

rating due to this construction. High wattage rating allows high peak current in operation.

However, this winding construction also induces a significant amount of induction which

is unavoidable even with the best non-inductive conductor/wires in the winding.

Therefore is it not suitable for the fast transient response of an ESD, as the stray

inductance from the resistor will induce a significant oscillation ringing to the discharge.

This can be overcome by damping with additional resistors, but the additional resistor

will further complicate the discharge circuit.



34

Film resistor are made by depositing a thin film of conductive material on to a insulator

solid then laser etched to provide required resistance [51]. Due to this construction, film

resistors have less stray inductance compared to wire wound. They also have large

resistance range and lower tolerance. Specially designed film resistors are able to achieve

GΩ resistances with kV ratings, making them suitable with one limitation. This limitation

is the stray inductance, which can be reduced with better quality resistors. Ideally, the

resistor can be manufactured with thinner layer of film allowing less stray inductance.

This holds true as technology advances, allowing higher quality resistors to be

manufactured.

In selecting the resistors for the high resistance high voltage divider bridge, the factors in

consideration are the stray capacitance, stray inductance, resistance value and the voltage

rating. Stray capacitance and inductance need to be limited through the type of resistor

construction. Resistor selection needs also to be in consideration of the feasibility of

achieving the resistance value and voltage rating. For example, it is possible to use 1,000

shunts to achieve the required voltage rating and voltage division. However, the cost and

connection of each shunt will induce more stray capacitance and inductance, rendering it

less applicable for the experiment Resistances needed are as described in Chapter 2.8.2

and they are 1 GΩ and subsequent 100 MΩ and 2 MΩ.

To bring the discharge voltage into range for measurement with a oscilloscope, an

attenuation of 1000X is required as the maximum expected voltage from discharge is 30

kV and the oscilloscope have a standard 30 V input. The internal impendence of the

oscilloscope is 2 MΩ, and thus the high voltage side requires a 2 GΩ resistance or greater

to achieve 1000X.



35

Figure 3.1.0.1 High Voltage Resistive Divider

The figure shows the high voltage resistive divider with 2GΩ

resistance in the high voltage side dropping 99.8% of the overall

voltage. The lower side is a 2MΩ estimation of the approximate

impendence of measurement equipment.

The high voltage resistive divider shows an example of the values required to meet the

measurement guideline. Further compensation is required to include the effect of the

measurement equipment into consideration.

3.2 Frequency Response of Resistive Divider

Due to the fast transient response of an ESD, the frequency response of the voltage

divider needs to be investigated. At steady-state or relative DC-state the expected

response of the high voltage divider is as it is expected. However, when recording the

discharge waveform, the fast response causes the high voltage divider to respond

unexpectedly. From the chosen resistors investigation is needed to determine their high

frequency response.



36

The Ohmite Mox series resistors are a thick film resistor [53], they are able to provide the

resistance and voltage rating for the simulation of ESD. The Ohmite MOX 108 resistors

are 1 GΩ, 20 kV rated with stated capacitance of 0.6 pF. The capacitance was confirmed

with a LCR meter at 1 kHz with measurements of 0.6-0.7 pF. The lower values at 100

MΩ and 2 MΩ did not register a value beyond noise signal.

To further examine the resistors at higher frequency, for stray capacitance and response, a

network analyser was used. The analyser used was a Rohde & Schwarz ZVL Network

Analyser 9 kHz-6 GHz [54]. Utilizing the network analyser’s feature of analysing the

return signal, the results of a S11 Linear Magnitude plot of impedances is shown below.

S-parameter measurement are the basic measurement method for a network analyser, they

provide the resulting signal that is reflected or transmitted through a device under test

[54].

Figure 3.2.0.1 1GΩ Frequency Response of Resistive divider in Linear Magnitude

Ω

Plot of the S11 analysis from the network analyser showing the

frequency response from 9 kHz to 6 GHz in linear magnitude Ω.

y = 8682.6x-0.226

R² = 0.0701

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0.E+00 2.E+08 4.E+08 6.E+08 8.E+08 1.E+09

Lin

ea

r M

ag

nit

ud

e,

Ω

Frequency, Hz



37

The above plot of the 1 GΩ resistor frequency responses shows the drop from1 GΩ

magnitude almost immediately after DC and at the lowest measureable frequency of 9

kHz the magnitude has decreased to 6,500 Ω, effectively reduces the resistor to non

operation past 9 kHz. Using the cut off frequency equation,

01 = 12 ∙ ∙ , ∙ $

(Eq. 14)

01 = 12 ∙ ∙ 1S ∙ 0.7D = 227VW

which gives a theoretical cut off frequency at 227 Hz using the manufacturer’s datasheet

[53]. This is consistent of the results, as past 227 Hz resistance will drop inverse

proportionally towards 0 Ω.

Similar results were recorded for 500 MΩ and 100 MΩ resistors of the same

manufacturer. The plots for the 500 MΩ and 100 MΩ are in Appendix 11.2 and 11.3

respectively.

From the frequency response results it is not possible to achieve accurate results with the

resistor divider as the performance of the resistor deteriorate immediately after DC at 227

Hz and have reduced to 0.00065% of the original 1 GΩ by 9 kHz.

3.3 Equivalent Capacitor Voltage Divider

In order to achieve a flat response from all frequencies from DC to 1 GHz, the resistive

voltage divider needs to be paired with a capacitive voltage divider. Referring to chapter

2.8.2 (Capacitor Compensation) and continuing with the example of High voltage

resistive from Chapter 3.1 (High Resistance High Voltage-Voltage Divider), the best

option is a compensated voltage divider. In order to maintain the same attenuation the

capacitance were chosen to be 10 pF and 10 nF. Figure 3.3.0.1 is the schematic of the

voltage divider.

To investigate the capacitive effect of the voltage divider, the sections of the divider were

analysed. Using the network analyser, the imaginary component of each section’s can be



38

plotted and capacitance calculated. The capacitance can be derived from the capacitance

reactance equation.

21 = −.2 ∙ ∙ 0 ∙ $

(Eq. 15)

Where f is the frequency and Xc and C are reactance and capacitance respectively. Since

capacitance is of interest here, only negative imaginary figures are of importance, they

will replace R in the frequency equation. Thus the equation becomes,

$ = −.2 ∙ ∙ 21 ∙ 0

(Eq. 16)

Using this capacitance equation, the capacitance as a frequency dependant can be

calculated and used for the voltage divider analysis. This method to evaluate the stray

capacitance can also be use to evaluate the overall capacitance of the voltage divider.

Results from the evaluation will allow a more precise measurement when attenuation and

measurement value is taken into consideration.



39

Figure 3.3.0.1High Voltage Capacitive Resistive Divider

The figure shows the example of resistive divider from Section 3.1

compensated with C1 and C2 to maintain attenuation of 1000X and

increases frequency performance from 227 Hz. C1 and C2 are 10 pF

and 10 nF respectively.

3.3.1Resistor-Stray Capacitance Evaluation

The Ohmite MOX 1 GΩ, 500 MΩ and 100 MΩ resistors were evaluated for their stray

capacitance at high frequency using the method described in the previous section. Plot of

the capacitance over frequency is as shown in Figure 3.3.1.1, where only the capacitance

is plotted and mean of the plot calculated. From the results, the mean stray capacitance

for the 1GΩ resistor is 4.15 pF.

The plot for 500 MΩ and 100 MΩ are shown in Appendix 11.4 and Appendix 11.5. The

mean stray capacitances calculated are 4.95 pF and 5.6 pF, respectively for 500 MΩ and

100 MΩ



40

Figure 3.3.1.1 Plot of 1GΩ Stray Capacitance Over Frequency

Plot of 1 GΩ resistor’s stray capacitance as evaluated over frequency

from 9 kHz to 1 Ghz. Capacitance value in F. Mean is calculated to be

4.15 pF

From the stray capacitance evaluation of Ohmite’s MOX series resistors, it is apparent

that further analysis is required for the final voltage divider. The results of 4.15 pF, 4.95

pF and 5.6 pF, for 1 GΩ, 500 MΩ and 100 MΩ were larger than expected and will affect

the attenuation of the voltage divider at high frequencies.

Table 3.3.1.0.1 Table of Stray Capacitance Results

Resistor Capacitance at high

frequency

1 GΩ 4.15 pF

500 MΩ 4.95 pF

200 MΩ 5.6 pF

0

2E-12

4E-12

6E-12

8E-12

1E-11

1.2E-11

0.00E+00 2.00E+08 4.00E+08 6.00E+08 8.00E+08 1.00E+09

Ca

pa

cita

nce

, F

Frequency, Hz

Mean=4.15E-12



41

3.3.2 High Voltage Capacitive Resistive Divider -Stray Capacitance Evaluation

Evaluation of the combined capacitive and resistive component for the voltage divider is

required, as the effects of stray capacitance from the resistive components are larger than

expected. 2 GΩ with 1 pF were tested in regards to capacitance at high frequency. The

mean capacitance was calculated to be 5.85 pF and the Plot of the 2 GΩ/1 pF is as shown

in Figure 3.3.2.1.

Figure 3.3.2.1 Plot of Coupled 2GΩ/1pF Capacitance over Frequency

Plot of capacitance of 2 GΩ coupled with 1 pF evaluated over

frequency from 9 kHz to 1 GHz. Capacitance value in F. Mean is

calculated to be 5.85 pF

Additional coupled sections were evaluated and the results are as follows. For the 200

MΩ/10 pF, the resultant capacitance over frequency is 73.5 pF and the 2 MΩ/220 pF

coupled section 452 pF. Plot for 200 MΩ/10 pF and 2 MΩ/220 pF are in the Appendix

section, Appendix 11.6 and Appendix 11.7

The expected value of the coupled 2 GΩ/1 pF section is 3.075 pF, compared to the

evaluated value of 5.85 pF which is a 90% increase. For the two couple sections

evaluated 200 MΩ/10 pF and 2 MΩ/220 pF, the results are 12.8 pF to 73.5 pF, 474%

difference and 220 pF to 452 pF, 105% difference.

0

2E-12

4E-12

6E-12

8E-12

1E-11

1.2E-11

1.4E-11

1.6E-11

1.8E-11

0.00E+00 2.00E+08 4.00E+08 6.00E+08 8.00E+08 1.00E+09

Ca

pci

tan

ce,

F

Frequency, Hz

Mean=5.85E-12



42

Table 3.3.2.0.1 Table of Evaluated Capacitance Results

RC pair Capacitance

2 GΩ/1 pF 5.85 pF

200 MΩ/10 pF 73.5 pF

2 MΩ/220 pF 452 pF

The capacitance of each evaluated coupled sections were significantly larger than

expected at high frequencies. The effects of this will need to be taken into consideration

when calculating the final attenuation for measurement calculation. This will have a

major impact on the measurement and will require each section to be tested in the final

design of the measurement circuit.

3.4 Oscilloscope Calibration

The oscilloscope is designed to match a probe of defined amount of resistance and

capacitance. This design is able to take that into account and correct for the true value of

the resistance and capacitance. A standard oscilloscope has a set internal resistance of 1

MΩ and an internal capacitance of up to 20 pF. This internal characteristic combined with

the measurement probe characteristic will create a significant error if not compensated

properly.

Standard probes 1X are terminated with a 50 Ω resistance with the cable contributing

additional 50 Ω and about 75 pF to ground. The oscilloscope is tuned to accept the

specifications of the probe and the capacitance can be trimmed to give a flat attenuation

to the frequency response. The simplified equivalent circuit is as shown in Figure 3.4.0.1.

This is the same for a 10X probe, where in addition to the terminating resistance and

cable capacitance and resistance, the probe also has a 9 MΩ resistor and ~10 pF in the

head of the probe. This allows an attenuation of 10X to be established with the 1 MΩ

internal resistance and ~90 pF cable plus internal capacitance. This allows the



43

oscilloscope to operate to higher frequency with DC response. The simplified equivalent

circuit is as shown in Figure 3.4.0.2.

Figure 3.4.0.1 Schematic of 1X Probe and Oscilloscope

Figure of 1X probe and oscilloscope, with equivalent components as

drawn. C1 and R1 are internal capacitance and resistance of the

oscilloscope. C2 and R2 are the probe characteristics, cable

capacitance and resistance, and terminating 50Ω resistor

Figure 3.4.0.2 Schematic of 10X Probe and Oscilloscope

Figure of 10X probe and oscilloscope with equivalent component as

drawn. It has the 1X probe configuration of C1 and R1 internal

capacitance and resistance of the oscilloscope, and C2 and R2 are the

probe cable characteristics. The addition components are the probe

head with C3 and R3 at 10 pF and 9 MΩ to give the 10X attenuation.



44

Using the Figure 3.4.0.1, it is possible to design the measurement circuit with

consideration to the oscilloscope. This will entail design considerations from frequency

response, attenuation, voltage ratings to input characteristic to the oscilloscope.

Component selection will be a key issue to complete this measurement circuit and

compensated it with regards to the oscilloscope.

3.5 Current Measurement

Current can be measured by using a small resistance in the discharge path. Using ohm’s

law current is given by

# = ) ∙ X, ) = #X

(Eq. 22)

A 0.1 Ω was to be used in the discharge return path to record the current flow during

discharge. The resistor along with cable and connection was evaluated using a network

analyser to record the frequency response in regards to impedance. The impedance

analysis of the section showed a varied response from 9kHz to 1GHz. The response is

split into 3 band for analysis and means for each band calculated. The low frequency band

is from DC to 200MHz where discharge has past the initial breakdown and has been

establish for some time. The calculated mean is 0.69+.972iΩfor the low frequency band.

The medium frequency band is from 200MHz to 500MHz and it occurs in the time period

immediately after breakdown and could contain continuous arcing period of the discharge,

with low distortions from breakdown or break off of arcing. The calculated mean is

0.50+4.20i for the medium frequency band. The initial breakdown is show as the high

frequency band with expected frequency at 500MHz and spikes of up to 1GHz. The high

frequency band has a mean calculated at 9.20+1.5iΩ. The response of the current

measurement section is show in figure 3.5.0.1, with frequency band showing means of

each band. This analysis has effectively banded the response of the component into

smaller frequency band in regard to the assumed characteristics of an electrostatic

discharge. The bands are the initial breakdown in high frequency, medium frequency

where arcing has been established and low frequency as arcing continues and breaks off.



45

From the mean value of the current measurement section, a characteristic of the current

measurement section can be recorded when used in combination with a compensated

oscilloscope and probe.

The increase in impedance as frequency increases in cable is described in various

literatures [55-57]. The 10 cm cable forming part of the current measurement section has

a profound effect on the overall characteristic and must be taken into consideration when

used for calculations.

Figure 3.5.0.1 Plot of 0.1Ω Current Measurement Section over Frequency

Plot of impedance of the current measurement section as evaluated by a network

analyser over frequency 9 kHz to 1 GHz. Impedance in Ω Ohms shown in 3

bands, Low, Medium and High Frequency Bands, with their respective means

0.69+9.72iΩ, 0.50+4.20iΩ and 9.20+1.53iΩ. Real values in red and imaginary

values in blue


3.6 Discharge Resistor High frequency Response

46


The discharge resistor is assessed for high frequency response due to the possible effect

of high frequency deteriorating the resistance value. Figure 3.6.0.1, is the plot of

discharge resistor over frequency. Similarly with the current measurement section, there

are distinct bands of frequency in which a single response is dominant. The low

frequency band is from DC to 100MHz and has the mean impedance of 38.72+107.38i Ω.

Medium frequency band is from 100MHz to 500MHz, with the mean impedance of

8.15+13.90i Ω. From 500MHz to 1GHz is the high frequency band and it has a mean of

5.68-0.78i

The results of the discharge resistor high frequency response warrant inclusion in the final

calibration and calculation of energy dissipation. The decrease from 1.5 kΩ to 5.68-0.78i

Ω, is significant to be utilised in the calculations. This analysis has effectively banded the

response of the component into smaller frequency band with respect to the assumed

characteristics of an electrostatic discharge. The three bands used are, the initial

breakdown in high frequency, medium frequency where arcing has been established and

low frequency as arcing continues and breaks off. Similarly with the current measurement

section, the analysis has identified key values in each band of frequency for the purpose

of estimating the discharge. By using the values to estimate response of components

during discharge, as discharge becomes both time and frequency dependent. This method

of approximating the component value for discharge response (high frequency response)

can be thought of as an extension of the numeric method for approximating an integrate,

but in the frequency analysis. Calculation of discharge energy is the integration of power

over time, the three frequency band estimation of component response allow a constant to

be used for their respective frequency response during discharge; thus simplifies the

discharge waveform to time dependant instead of both frequency and time dependant.



47

Figure 3.6.0.1 Plot of 1.5 kΩ Discharge Resistor over Frequency

Plot of impedance of the 1.5k Ω discharge resistor as evaluated by a network

analyser over frequency 9 kHz to 1 GHz. Impedance in Ω Ohms shown in 3

bands, Low, Medium and High Frequency Bands, with their respective means

38.72+107.38iΩ, 8.15+13.90iΩ and 5.68+0.78iΩ. Real values in red and

imaginary values in blue

3.7 Measurement Errors and Absolute Errors

From the measurement point of view, in terms of the measurement equipment to be used,

the errors can be limited and carried to the final measurement point. Measurement error

of component contains the absolute error of the multimeter used to test the components;

they are carried on to the measurement of the data with the oscilloscope’s own absolute

error. The relative errors can be tabulated for the measurement circuit and overall error

derived from the table. The overall error can be calculated from the following:

3456'7*8 6 = ± 12 :;<;=7= =8+578+4'8 >+'78

(Eq. 17)



48

,8'+*;>8 6% = ±+456'7*8 86=8+578 >+'78 × 100%

(Eq. 18)

Relative error in percentages can be added together to give the overall percentage error of

the final measurement. The final measurement’s absolute error can be calculated from the

overall error in percentages, by using equation 18.

±+456'7*8 86 = ,8'+*;>8 6% × =8+578 >+'78100%

So the final value should become measured value ± absolute error (final).

3.8 Conclusion

Analysis for the components to be used in a high voltage measurement circuit has found

that high frequency have a drastic de-rating effect on the component values. Stray

capacitance and inductance were present even after component criteria selection to limit

them. Analysis by a network analyser allows the establishment of an average value for

calculation purpose.

The analysis on the components in the discharge path has allowed an effective response to

be calculated when responding to the different periods in the discharge. Though crude,

the 3 band effectively signify the acting response of the component in their particular

frequency band with respect to the assumed characteristics of an electrostatic discharge.

This analysis simplifies a complex multivariable discharge waveform to a time dependant

waveform able to be integrated for energy.

Therefore, the only viable solution is to account for component values as assessed by a

network analyser as a final calibration of the measurement circuit, and the use those

values in the assessment for the overall measurement circuit characteristics


4.0 Low Voltage Discharge Simulation and Measurement

49


In order to clarify the energy dissipations of an electrostatic discharge (ESD), a simple

experiment involving lower voltage was set-up to simulate and measure an ESD at low

voltages. The aim of this experiment is to investigate the energy dissipation throughout

the circuit, especially during the initial high frequency and high impedance discharge at

the discharge point. This was done by measurements at the capacitor and discharge

resistor, which give us the differential voltage at the simulated discharge point.

Simulations of electrostatic discharges specified by IEC standards[7], has set parameters

such as rise time, discharge period and discharge current. Energy dissipation is calculated

from the general energy work equation, where C is capacitor, V is voltage and I is current.

( = 12 $ ∙ #, # = 1$ ) ∙ *

(Eq. 9)

However due to the low voltage and thus low energy of this experiment, energy

dissipated by other components of the circuit will be significant. As an extension to

research on hydrogen minimum ignition energy research [4], this experiment aims to look

at the discharge characteristics of the components in the circuit, where the spark energy is

the residual energy when energy in the resistor and capacitor residual energy is taken

away from the energy in the capacitor.

Es = Ec − Er − Eresidual, (Eq. 1)

In addition to measuring the voltage drop across the storage capacitor, the voltage drop

across the discharge resistor was also recorded. By combining the two measurements the

voltage drop across the discharge point can be recorded and energy calculated from the

voltage difference and current in the discharge.



50

Reference is made to conference paper “Simulation and Measurement of an Electrostatic

Discharge” in Appendix 10.8. This paper showed that the energy dissipated in the

discharge by the switch decreased in relation to the energy in storage capacitor, but rose

in relation to the peak current. The peak current increased as the resistor value decreased;

this increase of energy dissipation in the switch is more apparent than in discharge

resistor. The paper also showed that the characteristics of the connections impacted on the

data collected. No perfect discharges were recorded, where all energy was accounted for.

Therefore, if total energy present in the discharge circuit is in the storage capacitor then

the total energy dissipated in the switch and discharge resistor should equal the capacitor

energy. From the paper 5-15% energy was unaccounted presumed lost in the resistances

of the connections.

4.1 Low Voltage Discharge Simulation and Measurement Experiment

Method

By taking measurements prior and after the discharge point, the voltage drop and current

of the discharge can be recorded. This measurement of VI characteristic of the discharge

can be used to calculate the energy of the discharge and relate the energy to energy in the

capacitor.

A low voltage experiment designed to simulate the discharge was completed to provide

preliminary data on energy calculation. The experiment used a standard 30 V DC power

supply, charging a discharge circuit through a 560 KΩ resistor as show in Figure 4.1.0.1.



51

Figure 4.1.0.1 Schematic of the low voltage ESD simulation experiment

The capacitors ranged from 220 pF to 1.5 nF and the resistor from 330 Ω to 1.8

kΩ, values used for each set of tests are listed in Table 4.1.0.0.1.

Table 4.1.0.0.1 Table of experimental variables matrix for the low voltage ESD

simulation

# of Experiments R discharge

C storage 1.8kΩ 1.5kΩ 1kΩ 330Ω

1.5nF 10 10 10 10

1.2nF 10 10 10 10

1nF 10 10 10 10

680pF 10 10 10 10

470pF 10 10 10 10

220pF 10 10 10 10

Through the experiment matrix, the discharge characteristic can be investigated and the

effects of capacitance and resistance on energy dissipation can be recorded. It is expected

that large capacitance will deliver much higher energy dissipation and the range of

resistors should provide a choking effect to the flow of energy as the resistance is

decreased. This experiment is aimed to provide a trend characteristic to that effect, and

also derive the energy dissipation at the discharge point.

RDischarge

300 Ω~1.8 KΩ CStorage

220 pF~1.5 nF

30V

RCharge 560kΩ



52

Due to the low voltage, a spark over would not be possible and a switch was used to

simulate spark discharge. The discharge is measured by 100X voltage probes over the

storage capacitor and discharge resistor. The difference in these two reading gives the

voltage difference across the switch and gives a VI characteristic of the discharge.

For each variable set in the matrix 10 experiment results were recorded. Iteration

procedure is as follows,

1. The power supply is energised and a potential difference is seen on the oscilloscope.

2. The oscilloscope is set up to record on trigger when voltage on the storage capacitor

drops below 90%.

3. The switch is triggered, causing the discharge to occur and data recorded.

4. The system is reset for new iteration or new variable set


Results and Analysis

Referring to Appendix 10.8, voltage measurements at the two points Vc and Vr were

recorded. The difference of the two measured voltages gives the voltage drop across the

discharge point during discharge. Given the energy dissipated in the discharge resistor is

calculated from,

( = #Y, ∙ *

(Eq. 19)

and the energy dissipated at the discharge point is,

( = (#1 − #) ∙ #, ∙ *

(Eq. 20)

the unaccounted energy is given by

(7<+1167<*8 = (1+D+1;*6 − (85;5*6 − (;51ℎ+F8

(Eq. 21)



53

(1+D+1;*6 = 12 $ ∙ #

(Eq. 9)

(7<+1167<*8 = 12 $ ∙ # − #Y, ∙ * − (#1 − #) ∙ #, ∙ *

(Eq. 21)

Therefore, if total energy present in the discharge circuit is in the storage capacitor then

the total energy dissipated in the switch and discharge resistor should equal the capacitor

energy. From the paper 5-10% energy was unaccounted presumed lost in the resistances

of the connections.

Referring to Appendix 10.9, the results from the paper showed that the energy dissipated

in the discharge by the switch decrease in relation to the energy in storage capacitor, but

rose in relation to the peak current. It is expected that a larger capacitor will store a larger

amount of energy and therefore raises the overall energy dissipation in the discharge.

Therefore as the capacitance is decreased the energy dissipated at the discharge point

decreases. Overall, 80-90% of the total energy stored in the capacitor at discharge is

dissipated by the discharge resistor. In comparison, from Appendix 10.9, the largest

recorded average values for energy dissipated are 624nJ and 16.5nJ for the discharge

resistor and discharge point respectively. These results were for the 1.5nF capacitor

paired with 1kΩ. The stray resistance dissipated 35.5nJ of the initial 676nJ. However, the

results also showed that the peak current plays a major role in energy dissipation at the

discharge point.

The peak current increased as the resistor value decreased and increases the initial energy

dissipation in the resistive components. With a smaller resistance the inrush current will

peak at a higher point. The increase in peak current is inversely proportional to the

decrease of resistance. The results showed approximately a 600% increase in peak current

compare to 1/6 decrease in resistance. This is as expected as per ohm’s law,

# = ) ∙ ,, ) = #,

(Eq. 22)



54

as voltage remains constant, change in resistance will change the current. In this case the

discharging circuit initial voltage is V and discharge resistor is R. The initial current will

be relatively close in magnitude to the peak current.

Higher peak current will increase the energy dissipation at the initial discharge but should

deliver the same amount of overall energy as the initial energy in the capacitor remains

the same. However, the increase of peak current has been shown to increase the energy

dissipation at the discharge point as the discharge occurs. This increase of energy

dissipation is more apparent at the discharge point than at discharge resistor. However,

this phenomena accounts for only about 10% of the total discharge period and should be

more apparent for the high voltage simulations and experiments.

The main factor for the larger increase in energy dissipation at the discharge point

compared to at the discharge resistor, is that as discharge occurs the discharge point goes

from open circuit to short circuit, and effectively bridges the resistance from ∞ to 0 Ω.

Through ohm’s law it is clear that the larger peak current dissipates more energy as the

discharge point acts as a resistance in the transient phase

The fixed value components, the storage capacitor and discharge resistor, performed to

expectation with capacitors recording energy stored proportional to capacitor size and

independent of the resistor pair. Energy dissipation in the resistor responded according to

the size of capacitor with larger capacitor providing more energy for dissipation. There

slight increases in energy dissipated as the resistance is lowered; this is due to the effect

of peak current on the initial discharge. This is seen in figure 5 of Appendix 11.8, where

large peak current caused by the lower discharge resistance allowed a steeper trend of

energy dissipation at the discharge, as initial energy is decreased.


Discussion

The unaccounted energy mentioned in the previous section would be present in all

electronic circuits; it is only significant due to the relatively high amount with respect to

the low energy of the experiment. The peak current, 120mA in this experiment when

compared with the expected 30A in high voltage experiment, would cause the stray



55

resistance in the circuit to dissipate a more significant amount of energy in relation to the

milli-joule energy discharges. However, this resistance in comparison to the discharge

point and the discharge resistor would be much less than 5-15% of total resistance. As the

current is the same for a series circuit, energy dissipated by the resistance can be viewed

as percentage of total resistance, however this relationship is not apparent in the results.

At the smallest value of discharge resistor, the stray resistance was found to be 15-45 Ω.

It is not reasonable for stray resistance in the circuitry to accumulate to such large

resistance; therefore, it is possible that at the discharge, the transient effect of the

discharge effectively causes the discharge resistor to be a reduced resistance at high

frequency. If the resistance of the discharge resistor drops to a much lower value, a higher

percentage of energy would be dissipated at the discharge point and through the

connections and cables in the experiment. This phenomenon was investigated in Chapter

3.2 (Frequency Response of Resistive Divider), where resistors of high resistance stopped

performing at their rated value at high frequency. This requires further investigation for

confirmation and is further explored in chapter 5.

The increase in energy dissipation as capacitance increases is expected, however the ratio

of energy dissipated between the discharge point, the discharge resistor and the stray

resistance, is not proportional. The discharge resistor showed relatively consistent energy

dissipation when compared with difference size resistances of the discharge resistor. This

is somewhat expected as the majority of the energy is going to be dissipated by the

discharge resistor as the discharge resistor will continue to dissipate energy until the

charges of the storage capacitor are dispersed. The overall time will be much longer than

the initial discharge period, where the peak current will alter the energy dissipation. From

the analysis about 80-90% of the energy is dissipated by the discharge resistor and the

remaining 10-20% by the discharge point and the stray resistances. Furthermore it was

seen from the results in Appendix 10.9 that as the discharge resistance is decreased the

percentage of the energy dissipated by the discharge point increased. The increase at the

discharge point reduces the amount of energy dissipated by the stray resistance which

accounts for all the unaccounted energy lost from the initial capacitive energy. The

unaccounted energy is the residual energy after the discharge resistor and discharge point

energy dissipation has been subtracted from the initial capacitive energy.



56

The discharge resistor affects the peak current and the time constant of the overall

discharge. A smaller resistance will give a larger peak current and a shorter time constant

for discharge. It was seen from the results that there is a linear relationship between the

peak current and the resistance.

Overall energy dissipation should not be effected by the larger peak current with smaller

discharge resistor. The overall energy is determined by the stored charges in the storage

capacitor, which is derived from the capacitor size and voltage to which the capacitor is

charged. The higher peak current results in higher energy dissipation at the discharge

point. The discharge point can be considered to be an open circuit prior to discharge and a

short circuit after discharge. Therefore the discharge point would dissipate relatively large

energy in the transition period from open to short circuit. This is as expected as prior to

discharge there is infinite resistance across the discharge point. As the discharge connects,

the resistance at the discharge point approaches 0 Ω, and with the peak current flowing

will generate significant energy at that instant. The energy dissipation happens as

discharge occurs. During an actual discharge, energy would be converted to light and heat

as the discharge occurs, in which charges as electrical energy is dissipated. It is also noted

that energy will be radiated by the high frequency current flowing in the circuit.

The storage capacitor contains the majority of the energy discharged. It is possible for

charges to be flowing from the power supply during discharge, but this is limited due to

the large charging resistor selection. By selecting resistor values combined with the

storage capacitor to give a much longer charging time constant than the discharge period,

it is possible to limit this charging while the capacitor discharges. Therefore is expected

that the energy in the capacitor is independent of charging resistor and power supply, as

seen in the results of Appendix 10.9. Recorded waveform indicated the difference in the

charge and discharge time constants, with the slow ramp up to charged voltage at

significant time after discharge has occurred.

Energy dissipated by the discharge resistor is dependent on the initial amount of charges

in the capacitor. From the results in Appendix 10.9, the resistor will dissipate up to 90%

of the initial energy in the capacitor. Peak current has little effect on this energy

dissipated as the discharge period is much longer than the initial breakdown and majority

of the energy dissipated after the initial breakdown will occur at the discharge resistor. In


57

comparison, the overall discharge period is 200-300 ns, while the initial breakdown is 1

ns-10 ns. The breakdown and initial discharge is expected to have a large peak power,

however due to the duration of the initial discharge in the proportion to the overall

discharge. Energy dissipated will be relatively small and dependent on the peak current,

circuit stray resistance and initial breakdown transient duration.

4.4 Low Voltage Discharge simulation and Measurement Experiment

Conclusion

This low voltage discharge simulation and measurement experiment has provided the

basis for investigation of the energy dissipation in a discharge circuit. The importance of

inclusive energy dissipation in the discharge investigation is established, which is the

consensus of current literature.

The simplification of the discharge circuit and simulating discharge through a switch has

provided additional understanding and expectation of the discharge phenomena. This

simulation has also provided the basis for investigating the effects of varying capacitance

and resistance in the discharge circuit. Underlines the significance of the discharge

resistor on the induced peak current and the initial energy at discharge of the capacitor.


58

5.0 High Voltage Discharge Simulation and Measurement

Subsequent to the low voltage discharge simulation, theory and principles from previous

findings were considered to design the high voltage discharge simulation experiment. The

importance of discharge measurement, in particular the energy dissipation was reviewed

in previous chapters, Chapter 2.2 (Electrostatics) and Chapter 2.7 (Discharge Energy).

The discharge energy measurement needed to be investigated on a specifically designed

measurement system in order to achieve an accurate estimation of the minimum ignition

energy. However complexity of the measurement circuit will affect the measured values

as the effects of all the capacitance, inductance and resistance will impact on the energy

dissipation. In order to measure the high voltage at discharge, measurement circuit will

need to be tuned and compensated for the high frequency transient distortions. Referring

to Chapter 3 (High Voltage Measurement), each component and section of the

measurement circuit will need to be accounted for and investigated in relation to its

effects on the overall measurement. The aim is to achieve a flat response at high

frequencies and to be able to attenuate the high voltage to be captured by an oscilloscope.

This will allow an accurate capture of the voltage at discharge and allow the energy

dissipated to be evaluated.

Energy dissipation is the main focus of this simulation and experiment. From Chapter 2.7

(Discharge Energy), the initial capacitive energy of a discharge simulation can be

dissipated via the various components and the stray resistances. As seen in Chapter 4

(Low Voltage Discharge Simulation and Measurement), the discharge energy is not the

initial capacitive energy and the majority of the capacitive energy will be dissipated by

resistances in the discharge circuit. These resistances are the known discharge resistor,

unknown stray resistance and the equivalent resistance across the discharge point. The

aim of this simulation and experiment is to accurately assess the energy dissipation in a

simulated electrostatic discharge and allow discharge energy to be calculated for

minimum ignition energy investigations.



59

From the previous sections and investigations, a high voltage discharge experiment and

measurement circuit was designed, constructed and characterised for calibration.

Measurement circuit was simulated and analysed with respect to resistances and

capacitances at high frequency, to define the characteristic for energy dissipation

calculation. Attenuated voltage is recorded and converted for calculation and analysis.

Energy calculation is done on the recorded voltage and current, to calculate the initial

capacitive energy, discharge resistor energy and discharge point energy.

The results showed an overview of the high voltage discharge, with specific detail to


and peak current. The experiment presents a functional method for investigating the

energy dissipation, high voltage discharges and ignition energy of materials.

5.1 High Voltage Measurement Circuit

5.1.1 High Voltage Measurement Circuit Simulations

Due to this high voltage, measurement requires a specialised circuit, in which voltage

recorded becomes a fraction of the voltage measured. A simple resistive voltage divider

with high voltage components stepping down the voltage would be sufficient to measure

the high voltage before discharge. However, the transient effects of the discharge alter the

expected response of a resistive divider, and would require complex circuitry and

modelling to accurately derive the expected response. Special considerations need to be

taken into account as investigations showed in Chapter 3 (High Voltage Measurement).

The specific aspects that need to be assessed are the high frequency response of the

resistive divider, coupling compensation of the capacitive divider and the inclusion of

probe and oscilloscope into the overall assessment of the high voltage measurement

circuit.

To achieve the required attenuation for the high voltage measurement Ohmite’s Thick

Film resistors were chosen. These resistors were evaluated in Chapter 3 using a network

analyser and for the resistor values used 1 GΩ, 500 MΩ and 100 MΩ, the resistance was

found to have been reduced to less than 10 kΩ at 9+ kHz.



60

As the measurement is to the ground at the node with the discharge capacitor and at the

discharge point, the measurement circuit will need to have sufficient resistance to the

charging resistor to allow the capacitor to charge to high voltage. For example, if 500 MΩ

resistor was used as the charging resistor, a 1 GΩ voltage divider bridge will only allow

the experiment to operate at 66% of the input voltage at the high voltage power supply.

Therefore it was decided to use 500 MΩ and a divider of 2.2 GΩ to allow the maximum

voltage to rise up to 81% of the high voltage power supply.

As the discharge capacitor reduces as energy for discharge requirement decreases, a

minimum ratio of 50:1 was sought to be maintained, resulting in using a 1 pF capacitance

for the coupling of the 2.2 GΩ divider. This is in consideration to the charges stored in

the capacitive divider; the charges in the divider should be relatively small compared to

the charges in the discharge capacitor. By limiting a minimum ratio of 50:1, the effects of

the capacitive divider would be 2% or less.

The initial design of the measurement circuit is as shown in the Figure 5.1.1.1, the 2 GΩ

resistor coupled to a 1 pF capacitance, 200 MΩ coupled to 10 pF and a 2 MΩ coupled to

220 pF



61

Figure 5.1.1.1 Initial High Voltage Divider

The above is a schematic of the initial high voltage divider with only

consideration to the capacitive coupling and resistive division. The additional 200

MΩ section is for the use of a 100X probe.

The inclusion of a 200 MΩ coupled section is for the use of a 100X probe, where the

measured voltage is reduced to max of 1 kV from expected 10 kV discharge. This allows

the 100X probe to use its internal resistance to step down the voltage for the oscilloscope.

Standard oscilloscope will have a maximum ± 50 V input, which gives the voltage at DC,

based on the resistive divider a value of 917 V and for 100X probe 9.17 V. At high

frequency, using the capacitive divider the discharge will have increased to 946V and the

100X probe will further reduce it to 9.46 V. Due to the high frequency transient effects of

the discharge, as explored in Chapter 2.8 (HV Measurement) and Chapter 3 (High

Voltage Measurement), it is expected the resistive divider to cut out immediately after DC

and the capacitive divider to continue providing a flat response to high frequency. Figure

5.1.1.2 is the simulated frequency response of the divider at the 200 MΩ node using Spice.



62

Figure 5.1.1.2 Simulated Frequency Response of the Divider at 200MΩ node

Plot of the frequency response of the divider at 200MΩ, the divider out puts a flat

response from DC to 100GHz at the value of 917V, and switches to 946V for

1THz+

For a standard probe, the coupled capacitance of 220pF was used to allow better

resolution of the measured wave. At DC the expected voltage is 9V, calculated through

the resistive divider. Using the capacitive divider for high frequency, the discharge

expected would be 45 V at the 2 MΩ node. Similar to the results for the 200 MΩ node,

the resistive divider is expected to cut off immediately after DC and the capacitive divider

is expected to provide a flat response for high frequency. The Spice simulated response is

as shown in Figure 5.1.1.3.



63

Figure 5.1.1.3 Simulated Frequency Response for the Divider at 2MΩ Node

Plot of the frequency response of the divider at 2MΩ, the divider out puts a flat

response from DC to 100GHz at the value of 9V, then switches to 45V from

1THz+

Both simulations show relative flat response at high frequency, with a step up at 1THz.

This is not expected as the cut off frequency for the 2.2 GΩ resistors is 58 Hz. With the

resistive section to cut off at 58Hz when coupled with the 1pF capacitor and the series

stray capacitance of 0.7 pF from two 1GΩ resistors:

01 = 12 ∙ ∙ 2S ∙ 1.35D = 58VW

(Eq. 14)

The simulated result of resistive divider cut off at 1 THz is unexpected and with

consideration of resistor construction, the resistive divider should cut off at the estimated

58 Hz or lower. From Chapter 3.2 (Frequency Response of Resistive Divider), the 1 GΩ

resistors’ magnitude reduces from its initial 1 GΩ down to less than 6.5 kΩ by 9 kHz.



64

The resistive divider won’t be able to maintain the same ratio without the capacitive

divider holding up the ratio. The capacitor coupling retains the divider ratio as impedance

continues to fall and resistance effective becomes null after 10 kHz. Therefore it’s

assumed that after the cut off frequency of 58 Hz for the 2 GΩ divider section, the

response will rise to the capacitive divider response and by 10 kHz only the capacitive

divider will provide a response giving a flat output for high frequency.

5.1.2 High Voltage Measurement Circuit Evaluation

To investigate the response, a network analyser was used to evaluate the capacitive

component of each of the sections in the divider. Referring to Chapter 3.3 (Equivalent

Capacitor Voltage Divider) and using the results from the evaluation, the high voltage

divider is reassessed as show in Figure 5.1.2.1.

The stray capacitances were evaluated in Chapter 3.3.2 (High Voltage Capacitive

Resistive Divider- Stray Capacitance Evaluation) and the results are tabulated in 5.1.2.0.5

along with consideration to the coupling capacitor.

The capacitance of each evaluated coupled sections were significantly larger than

expected at high frequencies. The effect of the stray capacitance will be taken into

account in the following sections along with the effect to the overall attenuation. This is a

major impact on the measurement but the measurement calculations can be adjusted to

accommodate the effect.



65

Figure 5.1.2.1 Coupled High Voltage Divider

The above is a schematic of the coupled high voltage divider with the stray

capacitance evaluated by the network analyser. The stray capacitance adds an

additional 4.85 pF to the 2 GΩ/1 pF section, 63.5 pF to the 200 MΩ/10 pF section

and 252 pF to the 2 MΩ/220 pF section.

Table 5.1.2.0.5 Table of High Voltage Divider-Stray Capacitance Results

RC pair Total Evaluated Capacitance Stray Capacitance

2 GΩ/1 pF 5.85 pF 4.85 pF

200 MΩ/10 pF 73.5 pF 63.5 pF

2 MΩ/220 pF 452 pF 252 F

5.1.3 High Voltage Measurement Circuit Oscilloscope Compensation

Referring to Chapter 3.4 (Oscilloscope Calibration), oscilloscope can be reduced to a

parallel resistor and capacitor pair with probe cable resistance and capacitance. The



66

oscilloscope and probe cable need to be compensated for high frequency and the final

compensation and design need to be evaluated in the overall attenuation of the divider. A

1X probe will have a high frequency cut off at 6 MHz. By matching the capacitance and

resistances of the equivalent measurement circuit, a high frequency 2X probe can be

constructed. Figure 5.1.3.1 shows the compensated standard BNC/Alligator 1X probe and

oscilloscope with measured values of resistance and capacitance. Measurement of

resistance and capacitance was done with a LCR meter at 1 kHz. The probe

characteristics were 300 Ω cable resistance and 105 pF capacitance measured across the

line to ground with open circuit at one end. The oscilloscope was left floating and

measured to give 1 MΩ and 15 pF across the inputs. To obtain a 2X attenuation for the

probe and oscilloscope, the compensation was chosen to be 1 MΩ and 120 pF as the

probe tip.

Figure 5.1.3.1 Compensated 2X Probe Oscilloscope Equivalent Circuit

Figure shows the compensation for a 2X measurement probe oscilloscope

equivalent circuit. Compensation matched the probe cable and oscilloscope

resistance and capacitance creating a 2X probe for high frequency.

5.1.4 High Voltage Measurement Circuit Overview

From the investigation of this chapter, an assumed schematic is drawn for the

measurement circuit. The results from the evaluation of stray capacitance (Section 5.1.2)

300



67

and oscilloscope compensation (Section 5.1.3) are used to compile the final overview of

the equivalent measurement circuit. Figure 5.1.4.1 is the complete schematic of the high

voltage measurement circuit. The figure shows the complete schematic of the

measurement circuit, from the high voltage divider to oscilloscope including the

compensation and cable characteristic.

As mentioned previously probe cable and oscilloscope were measured for capacitance

and resistance, which allowed them to be compensated with a probe tip of 120 pF and 1

MΩ, creating a 2X attenuation. The capacitance and resistance from the compensation,

probe cable and oscilloscope will affect the high voltage divider and alter the attenuation.

To determine the final measurement circuit characteristic, the measurement circuit is

reduced to an equivalent circuit as show in Figure 5.1.4.2.



68

Figure 5.1.4.1 Complete High Voltage Measurement Circuit

Figure shows the schematic of the complete high voltage divider from the investigations. Sections shown are High Voltage Divider,

Compensation, Probe Cable and Oscilloscope. Values presents include measured values and compensated values.



69

Figure 5.1.4.2 Complete High Voltage Measurement Equivalent Circuit 1

Schematic of the complete high voltage measurement circuit with the simplified

oscilloscope, probe tip and probe cable equivalent.

Therefore, it is convenient to divide the attenuation assessment into DC response and high

frequency response. For the DC attenuation, only the resistance will be in effect and

provide an equivalent circuit as shown in Figure 5.1.4.3.



70


Schematic of the complete high voltage measurement circuit with simplified

oscilloscope, probe tip and probe cable equivalent in a DC assessment.

At high frequency the cable resistance of 300 Ω will still provide response to the high

frequency discharge. The cut off frequency of the probe cable is calculated by equation

14, assuming that the 1 MΩ resistor has null effect and the section then equates to a low

pass filter.

01 = 12 ∙ ∙ , ∙ $

(Eq. 14)



71

01 = 12 ∙ ∙ 300 ∙ 120D = 4.4:VW

(Eq. 14)

Therefore at 4.4 MHz the cable response will drop and provide a stray capacitance in

which at high frequency will be seen as a short circuit across the cable resistance. Thus at

the high frequency attenuation, only the capacitor will be in effect and provide an

equivalent circuit as shown in Figure 5.1.4.4.


Schematic of the complete high voltage measurement circuit with simplified

oscilloscope, probe tip and probe cable equivalent in a high frequency assessment.

Assuming high frequency at 4.4+ MHz, in which cable resistance act as short

circuit.

From Figures 5.1.4.3 and 5.1.4.4, the attenuation can be derived at which the measured

voltages at the oscilloscope need to be multiplied.



72

5.1.5 High Voltage Measurement Circuit Attenuation Calculation DC

Continuing on from Section 5.1.4 (High Voltage Measurement Circuit Overview), for an

attenuation at DC, the equivalent circuit as shown in Figure 5.1.4.3 can be further reduced

to a two value divider with the point of interest at the CRO, Probe & Cable node. This is

as shown in Figure 5.1.5.1.


Schematic of the complete high voltage measurement circuit with equivalent

values for DC analysis. Measurement side consist of oscilloscope, probe tip,

probe cable and low voltage side of high voltage divider.

Referring to Chapter 2.8.1 (Resistive Divider), the attenuation of the resistor divider is

given by,

+ = ,1 + ,2,2

(Eq. 10)

+ = 2.2S + 1:1: = 2201

(Eq. 10)

Therefore the DC attenuation is 2201X at the “CRO, Probe & Cable” node, with a 2X

probe compensation and adjusted for the oscilloscope.



73

5.1.6 High Voltage Measurement Circuit Attenuation Calculation High

Frequency

Similarly with the DC assessment (Chapter 5.1.5 High Voltage Measurement Circuit

Attenuation Calculation DC), the high frequency equivalent circuit can be further reduced

to a two value capacitive divider with the point of interest at the “CRO, Probe & Cable”

node. The result schematic is as shown below in Figure 5.1.6.1.


Schematic of the complete high voltage measurement circuit with equivalent

values for high frequency analysis. Measurement side consist of oscilloscope,

probe tip, probe cable and low voltage side of high voltage divider.

Referring to Chapter 2.8.2 (Capacitor Compensation), the attenuation of the resistor

divider is given by,

+ = $1 + $2$1

(Eq. 11)

+ = 5.419D + 512D5.419D = 95.48

(Eq. 11)



74

Therefore the high frequency attenuation is 95.48X at the “CRO, Probe & Cable” node,

with a 2X probe compensation and adjusted for the oscilloscope.

5.1.7 High Voltage Measurement Circuit Absolute Errors

Referring to Chapter 3.7 (Measurement Error and Absolute Errors), the measurement

errors are tabulated in the following Tables 5.1.7.0.1 and 5.1.7.0.2 along with the

accumulative relative errors for the final measurement. Absolute error calculation is used

for figures in section 5.3.2 (Experiment calculation and results), showing error bars in the

respective graphs.

Table 5.1.7.0.1 Resistive Measurement Error

Measurement

Point Measured

Value Absolute error of the

measurement

equipment

Relative

Error % Cumulative

Relative Error %

2 G/1 pF NA NA NA 0.00%

200 M/10 pF 200 MΩ 0.05 Ω 0.00% 0.00%

2 M/220 pF 2 MΩ 0.05 Ω 0.00% 0.00%

Probe Tip 1 MΩ 0.05 Ω 0.00% 0.00%

Probe Cable 300 Ω 0.05 Ω 1.67% 1.67%

Oscilloscope 1 MΩ 0.05 Ω 0.00% 1.67%



75

Table 5.1.7.0.2 Capacitive Measurement Error

Measurement

Point Measured

Value Absolute error of the

measurement

equipment

Relative

Error % Cumulative

Relative Error %

2 G/1 pF 5.85 pF 0.0005 pF 0.01% 0.01%

200 M/10 pF 73.5 pF 0.0005 pF 0.01% 0.02%

2 M/220 pF 452 pF 0.0005 pF 0.01% 0.03%

Probe Tip 120 pF 0.005 pF 0.01% 0.03%

Probe Cable 105 pF 0.005 pF 0.01% 0.04%

Oscilloscope 15 pF 0.005 pF 0.01% 0.05%

From the tables, the errors for resistive measurement will be ±1.67% and for capacitive

measurement ±0.05%. Using equation 18 the absolute values of the recorded values can

be derived.

±+456'7*8 86 = ,8'+*;>8 6% × =8+578 >+'78100%

(Eq. 18)

5.1.8 High Voltage Simulation

In the progress of developing sources of high voltage, three types generators were

evaluated and include the Van de Graff Generator, step-up transformers and switch mode

power.

Van De Graff Generators are based on the theory of triboelectricity and by using a

floating spherical conductor; charge can be stored and potential raised by triboelectricity.

Referring to the triboelectric table in Appendix 10.1, positive series materials are used in

conjunction with negative series material to strip charges from the positive series and

store the charges on the floating spherical conductor. An example of such setup is with

rubber in the form of a rubber band as the positive series material and a brass sphere as

the spherical conductor and the negative series material. The rubber band losses charges

to the brass through triboelectric effects and because the brass sphere is floating its able to

store the charges to an amount determined by the diameter of the sphere. The amount of

charge is limited by the materials used and the design of generator. It is quite able to



76

achieve high potential by increasing the amount of insulation and increasing the size of

the sphere to store more charges. However, to discharge the amount of charge for

experiments this generator is not feasible and manipulation of the charges would become

hazardous.

Transformers are able to provide step-up voltage to the required high voltage. A simple

premade setup is available that uses on a 555-timer that controlled the charging of a

1000:1 ignition coil acting as a step up transformer, taking power from a standard 12 V

battery. By using the IC controller, a bridge of Zener Diodes is used to hold the low side

voltage up to 225 V allowing pluses of high voltage up to 225 kV to be generated on the

high side. The simplicity of the design allows the charging process to be manipulated by

allowing a capacitor to be charged and discharged without restriking or continual voltage

supplied. The use of an ignition coil as the step up transformer allows the high voltage to

be achieved but adds a large amount of addition inductance. Additional inductance will

induce an oscillatory ringing effect in the discharge and significantly affect the discharge

waveform and energy. Significant alteration and design will need to be developed in order

to accommodate additional damping measures to combat the inductance from the ignition

coil. Induction would be best to avoided but is possible to be limited using damping.

Therefore the use of transformer would not be suited for short discharges with low energy,

but it might be suited for initial testing due to it cost and ease of setup.

Switch mode power supplies minimises the inductor required compared to using

traditional step-up transformer, and in a charge pump topology, only capacitors are used.

It is a specially designed circuit that controls the charging and discharging of an energy

storage device. The device is usually an inductor/transformer or capacitors in a charge

pump. By switching and controlling the charging and discharge process, voltage output

can be adjusted. Only a charge pump or switch capacitor topology can deliver high

voltage in the kilo voltage region. By switching between charging capacitors the

switching regulator creates an effect similar to a Cockroft Walton Voltage multiplier or a

Marx generator. As the capacitors are charged, additional capacitors start charging adding

the potential drop across each capacitor as the series charges. By using a switching

regulator, the charging process can be closely controlled and efficiency increased.



77

Switch mode power supply would be the ideal choice for the high voltage simulation

requirement of electrostatic discharge ignition experiments. It is possible to avoid or limit

inductance in the power supply and provide ease of control over the voltage and energy.

A specialist designed switch mode power supply is available at the specification required

for experiment. Those specification are ≥20 kV and ≥20 W, allowing the generator to

deliver 1 mA load current for charging. UltraVolt manufactured 30A24-30 high voltage

power supply was sourced for the experiment as it is most suited [58]. For this experiment

in high voltage measurement experiment a lower 10-12 kV is required, along with

reduced gap to simulate a lower energised discharge.

5.2 High Voltage discharge Experimental Method

5.2.1 High Voltage Experiment Circuit

From the design process of the last section, a measurement circuit is able to be

incorporated into the overall experimental circuit. The experiment setup includes a high

voltage power supply, charging resistor, discharge capacitor, discharge resistor, discharge

point, current measurement and the measurement circuit. Referring to Section5.1.8 (High

Voltage Simulation), switch mode power supply of a charge pump design was chosen as

the main power supply. This type of power supply is ideal for this experiment, due to the

relative low inductance introduced to the experiment circuit and the concise construction

compared to similar generators such as Cockroft Walton Voltage multiplier or a Marx

generator.

Referring to Chapter 5.1.1 (High Voltage Measurement Circuit Simulations), a 500 MΩ

charging resistor is required to charge the discharge capacitor and allow sufficient time

between charging to prevent continual discharge from the high voltage power supply. The

500 MΩ is in affect connected in series with the 2.2 GΩ measurement circuit, and by

using 500 MΩ will allow the voltage to be charged up to 81% of the power supply

voltage to be charged, while maintaining a large time constant in comparison to the

discharge.

The discharge capacitor is the main source of energy in the discharge. To ensure this, the

discharge capacitor will need to be at least 10 times larger than the capacitance in the



78

measurement circuit. From Figure 5.1.6.1, the overall capacitance in the measurement

circuit is 5.362 pF, which will contribute about 10% more capacitance to the overall

energy storage capacity for a 50 pF discharge capacitor. Thus, the discharge capacitor

selection needs to be take account for the effect of the measurement circuit when deciding

the size of the discharge capacitor.

Discharge resistor was selected to simulate the Human Body Model (HBM) simulation of

an electrostatic discharge (ESD). The resistor restrains the flow of current at discharge

simulating a longer discharge period, compared to a Charged Device Model (CDM)

simulation of an ESD. The resistor value as per HBM model is 1.5 kΩ.

Two electrodes manufactured to provide a parallel plate with a sharp point on the

discharge side of the electrode, were used as the discharge point. The electrodes were

used for easy modelling of the electric field induced prior to discharge. The effects of the

electric field prior to discharge have not been explored.

To calculate the energy dissipation in the discharge, current and voltage measurements

are required. From Chapter 3.5 (Current Measurement), the current measurement section

can be used with the compensated 2X probe and oscilloscope to acquire the current

measurement.

From the last section, Chapter 5.1 (High Voltage Measurement Circuit), a 2.2 GΩ high

voltage divider was designed. Referring to Figure 5.1.4.1 (Complete High Voltage

Measurement Circuit), the circuit consists of a high voltage divider, probe tip

compensation, probe cable characteristic and oscilloscope input impedances. The design

and evaluation of the high voltage measurement circuit response concluded that the final

attenuations are 2201 at DC and 95.48 at frequencies above 4.4 MHz from section 6.1.5

and 6.1.6 respectively. The measurement is to be taken via a compensated 2X probe and

oscilloscope.

The current measurement is conducted via the measurement of voltage across the current

shunt and recorded through a compensated 2X probe and oscilloscope. The current shunt

provides a small voltage drop across the resistance allowing current to be derived. The

current shunt is a 0.1 Ω shunt and with an 8.04 Ω magnitude at high frequency.



79

Figure 5.2.1.1 Overall Experiment Circuit

Figure is a schematic of the experiment circuit. It shows all section of the experiment from power supply, charging, discharge sections

and measurement circuit.



80

The overall experiment circuit is as show in Figure 5.2.1.1; it shows the high voltage

power supply, charging resistor, discharge capacitor, discharge resistor, discharge point,

current measurement and the voltage measurement circuit.

5.2.2 Experiment procedure

The procedure for experiment is as follow

1. Set discharge parameters such as atmosphere, discharge electrode separation and

discharge voltage, as shown in Appendix 10.10-12.

2. Initialise oscilloscope and set for trigger capture

3. Initialise high voltage power supply

4. Remove safety ground short

5. Trigger high voltage power supply to charge

6. Wait for discharge to occur and measurement recorded on the oscilloscope

7. Replace safety ground short if experiment concluded or repeat step 5 and 6

5.2.3 Energy Calculation

Referring to Section 4.4.2 (Low Voltage Discharge Simulation and Measurement

Experiment Results and Analysis), the energy in a discharge can be calculated from

( = (#1 − # − #;) ∙ #;X; ∙ *

(Eq. 20)

where Vc is the voltage at the capacitor and Vi is the voltage across the current measuring

resistor section, Zi. Vr is the voltage drop across the 1.5kΩ discharge resistor, impedance

Zr. Vr is given by,

# = ) ∙ X

(Eq. 22)

I is given by

) = #;X;

(Eq. 22)

Where Zi and Vi is the current shunt and voltage drop across the shunt. Vr becomes



81

# = #;X; ∙ X

And discharge energy equation (Eq. 20) becomes

(;1ℎ+F8 = (#1 − #;X; ∙ X − #;) ∙ #;X; ∙ *

Where Zr is 1.5kΩ and I is consistent due to series circuit arrangement for discharge

resistor and current measurement resistor

Energy in the capacitor is given by

(1+D+1;*6 = 12 $ ∙ #, # = 1$ ) ∙ *

(Eq. 9)

Energy dissipated in the discharge resistor is given by,

(85;5*6 = ) ∙ X ∙ *

(Eq. 19)

5.3 Results and Analysis

5.3.1 Discharge Current and Voltage Waveforms

Results were recorded from the two measurement points Vc and Vi, representing voltage

at the discharge capacitor and the voltage at the current measurement resistor. Referring

to the previous section Vr can be derived from the measurement of Vi. Plot of discharge

capacitor voltage and discharge current are as shown in Figures 5.3.1.1 and 5.3.1.2. The

plots show 15 discharges out of 17 recorded discharges. Two discharges were not

included due to measurement capture error.

Figure 5.3.1.1 also show a means plot of the 15 discharges, this was added to indicate the

similarities between all the discharges. The plots of the means identify the key features of

the discharge, namely, the charging voltage before discharge, the sharp transient at

discharge, the oscillations in the discharge and the state after the discharge.



82

The current plot, Figure 5.3.1.2, has two additional max and min plot in addition to the

means plots. The reason for the inclusion of a maximum and minimum plot is to identify

the peak current and current characteristic. The means plot identifies the key features of

the current waveform, namely, the initial peak current, the oscillation in the discharge and

the discharged state after the discharge.

The voltage at the discharge capacitor as shown in Figure 5.3.1.1 shows the voltage

before discharge and the sharp transient discharge in which the voltage falls. The voltage

was measured via a high voltage divider and a compensated measurement circuit with

oscilloscope. The recordings showed the stable voltage before discharge and discharge

itself with the final state charging back up to high voltage. Inductance cannot be avoided

but the circuit was designed to minimise its effect. However it was not expected the

limited inductance would induce the significant amount of oscillations seen in the

recorded waveforms. This inductance and associated oscillation derivate from the HBM

specifications but has minimal effect on the overall aim of the experiment. The overall

aim of the experiment is to simulate a high voltage discharge and measure it. The added

inductance complicates the assessment for energy dissipation, due to voltage and current

oscillation, dissipating the energy over a longer period of time.

The discharge current as shown in Figure 5.3.1.2 represents the measured current

waveforms from the discharges. Similar with the voltage waveform analysis, oscillation

in the discharge was unavoidable; even through inductance was limited through design

process. However, oscillation does not affect analysis as energy continues to be dissipated

in the oscillation. Inductance caused in the experiment, is a result of the simulation using

a HBM, but does not affect the aim of the experiment to measure the dissipated energy.

However, energy dissipation will be more complex as dissipation in the reverse path will

also need to be considered.



83

Figure 5.3.1.1 Experiment Results- Discharge Voltage Waveform at Discharge Capacitor

Plot of the discharge voltage at the discharge capacitor during the discharge period. 100 pF Discharge

-15000

-10000

-5000

0

5000

10000

15000

20000

25000

-1.00E-06 -5.00E-07 -3.00E-20 5.00E-07 1.00E-06

Vo

lta

ge

, V

olt

s

Time, Seconds

Exp. 275

Exp. 276

Exp. 277

Exp. 278

Exp. 279

Exp. 280

Exp. 281

Exp. 282

Exp. 283

Exp. 284

Exp. 285

Exp. 292

Exp. 293

Exp. 295

Exp. 296

Average



84

Figure 5.3.1.2 Experiment Results- Discharge Current Waveform

Plot of the discharge current over time during the discharge period. 100 pF Discharge

-15

-10

-5

0

5

10

15

-6.00E-08 -1.00E-08 4.00E-08 9.00E-08 1.40E-07 1.90E-07

Cu

rre

nt,

Am

ps

Time, Seconds

275

276

277

278

279

280

281

282

283

284

285

292

293

295

296

means

max

min



85

5.3.2 Experiment Calculations and Results

Summary of the discharge results are shown in Table 5.3.2.0.1. Results for each set of the

experiment are tabulated with the voltages at discharge, the energy in the capacitor, the

energy dissipated by the discharge resistor, the energy dissipated at the discharge point,

the unaccounted energy, and the peak current. Due to the effect of inductance on the

discharge, the results include negative value representing reverse path dissipation by the

reversed current.

The results include set of discharges (285 and 292) that appear to have re-strike after

initial discharge. This assessment is based on the lower voltage at discharge and the large

amount of unaccounted energy. The large percentage of unaccounted energy can be due

to initial overestimate of the capacitive energy, or a continued discharge, where the

previous discharge essentially have established a discharge path lowering the potential

required for discharge.

5.3.3 Discharge Voltage

Average voltage at discharge is 8,921.38 V, with maximum at 10,564.8 V and minimum

at 7,043.2 V. Due to the large attenuation in the DC measurement, Voltage at discharge

can vary greatly due to the limited resolution of the results captured. The smallest

increment is 0.4 V, which equates to 880.4 V. Therefore, assuming the maximum value

for DC measurement is ±3 V then 0.2 V measurement errors by the oscilloscope adds

addition 3.33% relative error to the overall measured value, make the overall relative

error 5%. The measured values would become 8,921.38±446.07 V for average,

10,564.8±528.24 V for maximum and 7,043.2±352.16 V for minimum, as shown in

Figure 5.3.3.1.



86

Figure 5.3.3.1 Plot of Discharge Voltage Results with absolute error

Figure of discharge voltages plotted with voltage and respective absolute error

for the measured result. Plots of 8,921.38±446.07 V average, 10,564.8±528.24V

max and 7,043.2±352.16 V min.



87

Table 5.3.2.0.1 Experiment Results-Summary of Discharge Energy Results for 100pF simulation and experiment

275 real imag 276 real imag 277 real imag 278 real imag 279 real imag

Vpeak 8804 Vpeak 10564.8 Vpeak 10564.8 Vpeak 8804 Vpeak 8804

Capacitor 3.80E-03 Capacitor 5.47E-03 Capacitor 5.47E-03 Capacitor 3.80E-03 Capacitor 3.80E-03

Resistor -4.92E-08 -1.11E-05 Resistor -7.43E-06 -3.92E-05 Resistor -7.05E-06 -3.83E-05 Resistor -1.10E-05 -4.80E-05 Resistor -1.29E-05 -5.33E-05

Discharge 8.14E-04 4.99E-04 Discharge 1.45E-03 1.46E-03 Discharge 1.45E-03 1.42E-03 Discharge 1.40E-03 1.64E-03 Discharge 1.43E-03 1.78E-03

Losses 65.70% 2.50E-03 Losses 47.69% 2.61E-03 Losses 48.34% 2.64E-03 Losses 21.41% 8.13E-04 Losses 17.33% 6.58E-04

Ipeak + 10.57 5.45 Ipeak + 10.83 12.77 Ipeak + 10.83 12.02 Ipeak + 10.83 14.46 Ipeak + 10.83 15.59

Ipeak - -9.56 -7.51 Ipeak - -10.83 -15.59 Ipeak - -10.83 -15.40 Ipeak - -10.83 -17.09 Ipeak - -10.83 -17.46


Vpeak 8804 Vpeak 8804 Vpeak 10564.8 Vpeak 10564.8 Vpeak 7043.2


Resistor -1.06E-05 -4.70E-05 Resistor -2.61E-07 -1.00E-05 Resistor -1.24E-06 -1.77E-05 Resistor -7.30E-07 -1.62E-05 Resistor 1.63E-06 -3.98E-06






Vpeak 8804 Vpeak 7043.2 Vpeak 8804 Vpeak 7043.2 Vpeak 8804


Resistor 9.23E-07 -5.45E-06 Resistor 9.45E-07 -2.46E-06 Resistor 2.66E-06 -1.04E-05 Resistor 2.20E-06 -3.49E-06 Resistor 8.09E-07 -1.69E-05







88

Summary Vpeak Capacitor Resistor- r I Discharge-r i Losses % Ipeak + Ipeak -

Average 8921.387 3.97E-

03 -2.81E-

06 -2.16E-

05 1.02E-

03 8.44E-

04 54.10% 2.12E-

03 9.99 -9.64

Max 10564.8 5.47E-

03 2.66E-

06 -2.46E-

06 1.45E-

03 1.78E-

03 79.45% 3.75E-

03 10.83 -10.83

Min 7043.2 2.43E-

03 -1.29E-

05 -5.33E-

05 3.52E-

04 1.49E-

04 17.33% 6.58E-

04 6.51 -6.26



89

5.3.4 Energy in the Capacitor

Energy in the capacitor is dependent on the voltage at and after discharge as capacitance

is fixed for this experiment. Referring to previous sections methods, the capacitive energy

is given by,

( = 12 $ ∙ #

(Eq. 9)

With capacitance constant, only voltage is a variable. As assessed above, limited

resolution of the results contributed to a larger measurement error for this measurement of

voltage at DC prior to discharge. The 5% DC voltage relative measurement error equates

to 10% error on capacitive energy calculation. The capacitive energies recorded were

3.97±0.397 mJ average, 5.47±0.547mJ maximum and 2.43±0.243 mJ minimum, as shown

in Figure 5.3.4.1.

Figure 5.3.4.1 Plot of Initial Capacitive Energy with absolute error

Figure of initial capacitive energy in mJ with respective absolute error for the

calculated result. Plots of 3.97±0.397 mJ average, 5.47±0.547 mJ max and

2.43±0.243 mJ min.



90

5.3.5 Discharge Resistor Energy Dissipation

Energy dissipated by the discharge resistor is determined by the current as voltage over

the resistor was not measured. Current is derived from the voltage over the current

measurement resistor via Ohm’s law.

) = #;X;

(Eq. 22)

The current is then used to calculate the energy dissipation in the discharge resistor

through the use of Ohm’s law and energy dissipation in a resistor

# = ) ∙ X

(Eq. 22)

( = #X ∙ * = ) ∙ X

X ∙ * = ) ∙ X ∙ *

(Eq. 19)

This gives the following equation for energy dissipated in the discharge resistor through

calculation of current from the current measurement resistor.

( = (#; X;⁄ ) ∙ X ∙ *

(Eq. 19)

Energy dissipation calculated using the above equation is tabulated in Table 6.3.2.0.1.

Given real power dissipation is of interest, only the real energy dissipated is mentioned

and plotted here. The results show an average of -2.811 uJ dissipated, with maximum as

high as 2.66uJ and minimum as low as -12.897 uJ.

Additional measurement error caused by absolute error 0.2 V in the oscilloscope accounts

for a much smaller error as the resolution of the discharge is ±50 V. The relative error to

be added is 0.2% to give the overall relative error 0.25% and 0.5% for energy calculation.

This amends to the results to -2.811±0.014 uJ average, 2.66±0.013 uJ maximum and

-2.897±0.064 uJ minimum as shown in Figure 5.3.5.1.



91

Figure 5.3.5.1 Plot of Discharge Resistor Energy Dissipation with absolute error

Figure of discharge resistor energy dissipation in mJ with respective absolute

error for the calculated results. Plots of -2.811±0.014 uJ average, 2.66±0.013 uJ

max and -2.897±0.064 uJ min.

5.3.6 Discharge Point Energy Dissipation

Referring to the previous section, discharge point energy dissipation is given by,

( = (#1 − #;X; ∙ X − #;) ∙ #;X; ∙ *

(Eq. 20)

Where Vc is the voltage at the capacitor, Vi/Ri is the current flowing during the discharge

and R is the discharge resistance. Due to the method of calculating energy dissipation,

both real and imaginary values need to be included. The real values represent real energy

dissipation by resistive elements, while the imaginary values represent energy being

stored or discharged by inductive and/or capacitive elements.

The same overall relative error of 0.25% is maintained giving the energy calculation a

relative error of 0.5%. The results for real energy dissipation are 1.023±0.005 mJ average,

1.454±0.007 mJ maximum and 0.352±0.002 mJ minimum. For the imaginary energy



92

dissipation, average is 0.844±0.004 mJ, maximum is 1.78±0.009 mJ and minimum is -

1.49±0.007 mJ. The energy dissipation values are plotted in Figure 5.3.6.1 along with

results tabulated in Table 5.3.6.1.1.

Figure 5.3.6.1 Plot of Discharge Point Energy Dissipation with absolute error

Figure of discharge point energy dissipation in mJ with respective absolute error

for the calculated results. Plots of 1.023±0.005 mJ average real, 1.454±0.007 mJ

max real 0.352±0.002 mJ min real. 0.844±0.004 mJ average imaginary,

1.78±0.009 mJ max imaginary and 1.49±0.007 mJ min imaginary.

Average real,

1.02E-03

Maximum real,

1.45E-03

Minimum real,

3.52E-04

Average imaginary,

8.44E-04

Maximum

imaginary, 1.78E-

03

Minimum

imaginary, 1.49E-

04

0.00E+00

2.00E-04

4.00E-04

6.00E-04

8.00E-04

1.00E-03

1.20E-03

1.40E-03

1.60E-03

1.80E-03

2.00E-03

En

erg

y i

n m

illi

-Jo

ule

s, m

J



93

Table 5.3.6.1.1 Discharge Point Energy Dissipation Results

Real Energy in mJ Average real Maximum real Minimum real

Discharge Point 1.0234E-03 1.4542E-03 3.5234E-04

± 5.1170E-06 7.2709E-06 1.7617E-06

Imaginary Energy in mJ Average imaginary Maximum imaginary Minimum imaginary

Discharge Point 8.4395E-04 1.7788E-03 1.4911E-04

± -4.21977E-06 -8.89417E-06 -7.4553E-07

5.3.7 Unaccounted Energy Results Summary

The unaccounted energy is the difference between the energy supplied by the capacitor

and the energy being dissipated in the discharge resistor and discharge point. Since all

energy is from the capacitor, unaccounted energy is the residual energy after both real and

imaginary energy in the circuit as been accounted. The overall equation with respect to

the above energy calculation equation is,

(7<+1167<*8 = 12 $ ∙ # − (#; X;⁄ ) ∙ , ∙ * − (#1 − #;X; ∙ X − #;) ∙ #;X; ∙ *

(Eq. 21)

The unaccounted energy or lost energy is tabulated in Table 5.3.2.0.1. The results were

shown both as in joules and in percentage of the initial capacitive energy.

Due to the limited resolution of the discharge voltage, the unaccounted energy record

varies greatly as it depends on the calculated capacitive energy. The results from Table

5.3.2.0.1 show the average unaccounted energy at 2.12 mJ/54.10% of the initial

capacitive energy, with max at 3.75mJ/79.54% and min at 0.658mJ/17.33%.

Table 5.3.2.0.1 Unaccounted Energy Result Summary

Energy in mJ Average Maximum Minimum

Unaccounted 2.12E-03 3.75E-03 6.58E-04

% of initial Cap 54.10% 79.45% 17.33%

5.3.8 Peak Current

The peak discharge current is the maximum value recorded by the current measurement

resistor. Peak current has a significant effect on the energy dissipation during the initial



94

discharge. Referring to Chapter 4 (Low Voltage Discharge Simulation and Measurement),

the high peak current dissipates significantly larger amount of energy when compared to

overall energy dissipation throughout the discharge. Only real current is of interest as

imaginary current is either charging or discharging storage elements in the circuit.

Peak current results from Table 5.3.2.0.1 are shown with positive and negative peaks,

giving two sets of peak current results. Positive peak currents are 9.99 A average, 110.83

A maximum and 6.51 A minimum. Negative peak currents are -9.64 A average, -10.83 A

maximum and -6.26 A minimum.

From Table 5.1.7.0.1, measurement error from the oscilloscope is 4.33%. The peak

current with absolute error is as show in Table 5.3.8.1.1 and plotted in Figure 5.3.8.1.

Figure 5.3.8.1 Plot of Peak Current with absolute error

Figure of Peak current during discharge in amperes with absolute error from

measurement. Plots of peak currents, 9.99±0.43 A average+, 10.83±0.47 A max+,

6.51±0.28 A min+, -9.64±0.42 A average-, -10.83±0.47 A max-, and

-6.26±0.27 A min.

Average +, 9.99

Maximum +, 10.83

Minimum +, 6.51

Average -, -9.64

Maximum -, -10.83

Minimum -, -6.26

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

Cu

rre

nt

Am

pe

res,

A



95

Table 5.3.8.1.1 Peak current summary

Current,

Amps Peak Current ±

Average + 9.99 0.43

Maximum + 10.83 0.47

Minimum + 6.51 0.28

Average - -9.64 -0.42

Maximum - -10.83 -0.47

Minimum - -6.26 -0.27

5.4 Discussion

5.4.1 Discharge Current and Voltage Waveform Discussion

Looking at the captured waveforms in Section 5.3.1 (Discharge Current and Voltage

Waveform), significant oscillation is present, which suggest the design process to limit

inductance was not entirely successful. Inductance can be derived with the assumption

that capacitance total is 105.85 pF (discharge capacitor in parallel with measurement

circuit capacitance) and that the oscillation at 20 nS period is natural frequency. The

equation for natural frequency is,

/G = 1√I ∙ $ , /J = 2K

(Eq. 23)

I = 1$ ∙ /J = 1105.85D ∙ 220< = 95.81<V

By the above assumption an inductance of 95.81 nH is calculated. If the above inductance

is assumed, from the damping factor equation using a damping factor of 1.0, R would be,

L = ,2 M$I

(Eq. 24)

, = 2L_$I

= 2_105.85D95.81<

= 60.17Ω

Assuming period of oscillation at 20 nS, the frequency of the oscillations at discharge

would be 50 MHz for this experiment. Therefore, 60.17Ω resistance is required to

critically damp the circuit. This reinforced the theory that at initial discharge the high



96

response transient effectively renders the resistor in the circuit null, since there a 1.5kΩ

discharge resistor in series with the inductance and capacitance, which with respect the

above analysis would suggest it has to drop below 60.17 Ω at the discharge. This

confirmed by the discharge resistor assessment in section 3.7 (Discharger Resistor High

Frequency Response), where high frequency response at 250MHz + is less than 10 Ω.

This adds to the already large frequency disruption from the transient discharge, with

initial peak frequency of 500 MHz-1GHz from the >1 nS rise time seen in the experiment.

In regards to energy dissipation, oscillations would not affect the overall energy

dissipation. Energy dissipation would be considered in absolute; in both positive and

negative directions.

The lack of resolution at DC for the voltage waveform induced a significant error to the

measurement, as shown in Figure 5.3.1.1. Relative measurement error from the

oscilloscope is 3.33%, calculated from the maximum value of 3V with 0.2V measurement

error. The relative error equates to 440V at the final reading and compared to the 5kV

difference between the minimum to maximum recorded voltage, the lack of resolution

become apparent.

The high frequency sections of the voltage waveform include a large number of

oscillations. This emphasises the importance of limiting inductance in the experiment

circuit. The use of capacitive divider for the high frequency response is show as effective

as the 50 MHz oscillation from the discharge has been captured with limited distortion.

Looking at the current waveform, there is significant oscillation present due to stray

inductance. Inductance was limited during design and modelling of the investigation,

however through the analysis it was found that a small amount 95.81nH estimated is

present at discharge. Every component will have some inductance; the inductance could

be due to effect of high frequency response of the component, induced through the design

and manufacture the individual components. Another source of possible inductance

would be the arrangements of the connections and connecting cables.



97

5.4.2 Results Summary-Discussion

The tabulated results in Table 5.3.2.0.1, is a summary of the experimental results and

calculations. The tabulated results show where possible real and imaginary parts of the

represented values. The inclusion of complex calculation through the impedance allows a

closer look at the energy interactions in this circuit. Imaginary energy dissipation is not

real energy dissipated, it signifies the energy being used to charge or discharge from

storage element such as inductors and capacitors.

5.4.3Discharge Voltage-Discussion

Due to the large attenuation in the DC voltage measurement, resolution of the

measurement is significantly limited. Smallest increment in measurement is 880 V for the

overall max ±30 kV measurement setup, representing 3.33% relative measurement error

to the oscilloscope and taking the overall relative error to 5% for DC voltage

measurements. Results showed average of 8,921 V, which is close to the estimated 9 kV

for a 3mm gap. The experiment is set up to charge till break down across the gap. The

high voltage is reduced by the charging resistor to 81% of the high voltage at the supply.

Therefore, if maximum recorded voltage was 10,564 V then the maximum supply voltage

is 13,041 V.

5.4.4 Capacitor Energy-Discussion

The 10% relative error for the energy in the capacitor energy calculation represents a

significant amount of disputable energy. This is a direct result of the limited resolution on

the DC measurement. As the energy is dependent on the capacitance and voltage, the

large increment in the voltage measurement reduces the accuracy of the initial energy

evaluation. Capacitance is constant for this experiment, thus the wide range in energy

calculated is due to the voltage variation. Energy calculated ranged from 2.43 mJ to 5.43

mJ; voltage volatility is thus noted.

5.4.5 Discharge Resistor Energy Dissipation-Discussion

Energy dissipation in the discharge resistor is dependent on the resistance and current in

the discharge. Given that resistor is constant for this experiment, the current is the main



98

variable. The current is derived from the current measurement results and it is used in

equation 19 to calculate the energy dissipation.

( = ) ∙ X ∙ *

(Eq. 19)

Current measurement derived from measured voltage over the current measurement

resistor give a low measurement error of 0.45%. The current measurement section

contains just the resistor acting as a current shunt in which voltage drop is measured. It

was unexpected that such low resistance would be affected by the high frequency but as

evidenced in Section 3.5 (Current Measurement) the resistor exhibited higher impedance

as frequencies increased. There will be a large increase in resistance at high frequency

due to skin effect which is a result of the limitation on the design and manufacture, an

adverse effect to high frequency. Further research would be required to determine high

frequency component for measurement.

5.4.6 Discharge Point Energy-Discussion

Discharge point energy is calculated by the voltage difference at the discharge point and

the current through the discharge. Absolute values were used for the final calculation and

the importance of polarity of the energy was noted. Results indicate that a higher voltage

was recorded at the discharge resistor due to inrush of current from ground as discharge

occurs; this creates a negative readings. However, the reverse orientation and oscillatory

ring does not impact on the overall measurement as the absolute energy dissipation

reading is recorded and overall absolute value of the energy dissipation is calculated from

the recordings.

5.4.7 Unaccounted Energy-Discussion

Due to the complex calculation, we can see that not all the initial energy is dissipated by

resistance. Significant complex imaginary energy is used from the initial energy to charge

other storage elements in the discharge circuit. These elements are either inductive or

capacitive. The energy is the remaining unaccounted energy from calculation and can be

up to 80% of the initial energy. Average of 54% is high considering energy unaccounted


99

dissipation due to stray resistances in the circuit and accuracy of measurement. The ±10%

measurement error contributes greatly to the accuracy of this outstanding energy

calculation. However, even with the consideration of absolute measurement error, there is

no doubt unaccounted elements in the circuit dissipates a significant amount of the initial

discharge energy. Further investigation would be required to understand the effect on this

minuscule time frame of an electrostatic discharge.

5.4.8 Peak Current-Discussion

Currents were calculated at 0.4pS measurement periods by the measurement circuit

through the arrangement of oscilloscope, probe and current measurement circuit. 0.4 pS is

the minimum time increment on the oscilloscope. This provided a relatively accurate

measurement at ±4.33% relative measurement error.

5.5 High Voltage Discharge Simulation and Measurement- Conclusion

Through this investigation, a high voltage discharge experiment was designed constructed

and characterised for calibration and energy dissipation calculation. The circuit was

defined in accordance to impedance and capacitance with respect to high frequency,

which allows the characterisation of the circuit for energy dissipation measurement and

calculation.

The findings showed an overview of the high voltage discharge, allowing details such as


and peak current to be investigated. The resulting experiment presents a functional

method for investigating the energy dissipation in high voltage discharges and ignition

energy of materials.


6.0 Materials Ignitions

100


6.1 Introduction

The design, fabrication and validation of the developed discharge system described,

enables the study of the energy required to ignite a material. Chapter 5 (High Voltage

Discharge Simulation and Measurement) validates the developed system, capable of

determining the discharge energy required for ignition. Systematic experiments were

conducted to determine the minimum ignition energy for a simulated electrostatic

discharge on a liquid phase fuel.

The discharge capacitor is the main variable in which energy is stored and discharged. As

successful ignitions of the fuel are confirmed, capacitor values are decreased till no

ignition occurs. The discharges are recorded to calculate energy dissipation as described

in Chapter 5, in particular Section 5.2.2 (Energy Calculation). Energy dissipation results

are then used in a probability analysis to determine the minimum ignition energy.

The fuel material chosen for this experiment is liquid n-Pentane and was chosen due to its

insulative properties and its low ignition energy requirement. It was determined during

the initial search for appropriate fuel material that insulative properties are required for

ignition to occur in a simulated electrostatic discharge (ESD). Additionally, the previous

and related recent works on n-Pentane and associated researchers would allow some

indication to the validity of the results.

A suitable material was sought with the following parameters, low electrical conductive

factor, low ignition energy, and readily available. Hydrocarbons were ideal, with low

ignition energy required [59] and n-pentane matching the low electrical conductive factor

[25] and readily available in the laboratory.

.

High voltage ignition energy measurements of n-Pentane were conducted for 0.5ml n-

Pentane solution evaporated in a 250 cm3 chamber. It was determined that the minimum

require energy for ignition of n-Pentane from the experiments conducted was 0.352mJ,



101

and statistical analysis result for a 1% probability of ignitions (P=0.01) the energy is

0.269 mJ, for a 50% ignition (P=0.5) the energy is 0.448 mJ and for 99% ignition (P=0.99)

the energy is 0.627 mJ. From the results, the importance of circuit configuration on the

discharge characteristic and ultimately the ignition energy can be determined.

6.2 Method

This investigation of the ignition energy requirement for n-Pentane carries on from

Chapter 5, using the same measurement setup described in Section 5.2.1 (Experiment

Circuit) and using the energy calculation method in Section 5.2.3 (Energy Calculation).

The ignition energy calculated is then used to determine the probability of ignition

through the collected data of discharges. The ignition energy is controlled through the

careful variation of discharge capacitor value. By decreasing the capacitance, it is

possible to approach and determine the minimum value of capacitance in which ignition

will occur and from the results calculate the ignition energy in the discharge and the

ignition probability.

The n-Pentane was deposited in the base of the glass chamber shown in Appendix 10.11

and allowed to evaporate in the chamber. Ignition test then were conducted with the

following procedure.

1. Set discharge parameters such as atmosphere, discharge electrode separation and

discharge voltage, as shown in Appendix 10.10-12

2. Initialise oscilloscope and set for trigger capture

3. Initialise high voltage power supply

4. Deposit 0.5mL of n-Pentane solution to discharge point.

5. Remove safety ground short

6. Trigger high voltage power supply to charge

7. Wait for discharge to occur and measurement recorded on the oscilloscope

8. Replace safety ground short if experiment concluded or repeat Steps 6 and 7

9. If ignition does not occur after 3 tests, chamber is flushed, ground link replaced

and repeat Steps 4-8.



102

6.3 Results and Analysis

Ignitions experiment results are tabulated in the Table 6.3.0.0.1. The results are split into

ignition and no ignition sections, with the summarised analyses on the right. First set of

results in blue are the ignited results. The second set of results in red is the non-ignition

results. A Summary of the two sets of result is at the end of the table. Twenty-one sets of

data were used in the ignition analysis of the overall 49 set of results. The ignition results

are a mix of all the ignition experiments with focus only on the energy dissipated instead

of capacitor value. An example of the discharge can be found in the frame extracts from

the high speed camera in Appendix 10.13. The entire experiment result can be located in

Appendix 10.14.

6.3.1 Ignition Energy and Minimum Ignition Energy

As shown in Section 6.3.6, the ignition energy is calculated via

( = (#1 − #;X; ∙ X − #;) ∙ #;X; ∙ *

(Eq. 20)

The results are tabulated in Table 6.3.0.0.1. The lowest recorded confirmed ignition and

its ignition energy is 0.352 mJ with exclusion to re-strike arcing. In comparison the

standardised testing derived from Lewis and von Elbe stated a 1% probability of ignition

requires 0.28 mJ [60], results from Moorhouse [59] stated 0.5mJ and work by Calcote [61]

show 0.6 mJ lowest ignition energy.

6.3.2 Ignition Probability Statistical Analysis

Probability of ignition was analysed with respect to a binomial statistical modelling, using

Logistic Regression Method to analyse a Bernoulli ignition/no ignition statistic of the

ignition results [62]. The resultant S-Curve gives a good indication of the probability of

ignition from the binary (True/False) ignition/no ignition results. The S-curve defines the

probabilities of ignition with a mid-transition zone, where probability of ignition

increases exponentially from no ignition to ignition. This analysis is ideal solution for a

statistical analysis of ignition results as the data are not normally distributed. The

probability of ignition is given as:



103

Table 6.3.0.0.1 Ignition and No Ignition Discharge Result Summary


Vpeak 8804 Vpeak 7043.2 Vpeak 8804 Vpeak 7043.2 Vpeak 8804


Resistor -4.92E-08 -1.11E-05 Resistor 9.45E-07 -2.46E-06 Resistor 2.66E-06 -1.04E-05 Resistor 2.20E-06 -3.49E-06 Resistor 8.09E-07 -1.69E-05






Vpeak 8804 Vpeak 7043.2 Vpeak 7043.2 Vpeak 7043.2 Vpeak 10564.8


Resistor 2.04E-06 -8.56E-06 Resistor -2.62E-06 -1.00E-05 Resistor -1.52E-06 -5.42E-06 Resistor 8.65E-07 -3.12E-06 Resistor 1.74E-06 -1.14E-05

Discharge 9.16E-04 4.73E-04 Discharge 2.47E-04 4.52E-04 Discharge 1.01E-04 2.29E-04 |Discharge| 3.52E-04 1.97E-04 Discharge 1.02E-03 6.15E-04




361 real imag 362 real imag 363 real imag

Vpeak 8804 Vpeak 8804 Vpeak 8804

Capacitor 2.25E-03 Capacitor 2.25E-03 Capacitor 2.25E-03

Resistor 1.64E-06 -8.34E-06 Resistor -2.54E-06 -1.90E-05 Resistor -5.93E-06 -2.39E-05

Discharge 7.73E-04 5.17E-04 Discharge 8.50E-04 8.60E-04 Discharge 6.24E-04 1.04E-03

Losses 42.91% 9.65E-04 Losses 24.89% 5.59E-04 Losses 27.13% 6.10E-04

Ipeak + 10.83 5.63 Ipeak + 10.83 8.07 Ipeak + 10.83 4.13

Ipeak - -9.47 -6.76 Ipeak - -10.15 -10.14 Ipeak - -5.33 -17.65



104


Vpeak 7043.2 Vpeak 5282.4 Vpeak 5282.4 Vpeak 10564.8 Vpeak 10564.8


Resistor -1.34E-06 -5.12E-06 Resistor 6.15E-07 -3.85E-06 Resistor 2.53E-07 -3.87E-06 Resistor -7.31E-07 -1.94E-05 Resistor 5.70E-07 -1.27E-05






Vpeak 5282.4 Vpeak 5282.4 Vpeak 7043.2 Vpeak 7043.2 Vpeak 7043.2


Resistor 6.40E-07 -2.15E-06 Resistor -6.40E-07 -4.47E-06 Resistor 3.02E-07 -3.20E-06 Resistor -7.09E-07 -6.24E-06 Resistor -1.69E-08 -4.98E-06





Ignition Average Max Min No Ignition Average Max Min

Vpeak 8483.855 10564.8 7043.2 Vpeak 7043.2 10564.8 5282.4

Capacitor 2.78E-03 3.80E-03 1.69E-03 Capacitor 1.44E-03 3.24E-03 6.28E-04

Resistor 3.98E-07 -1.08E-05 2.66E-06 -2.46E-06 -5.93E-06 -2.39E-05 Resistor -1.06E-07 -6.59E-06 6.40E-07 -2.15E-06 -1.34E-06 -1.94E-05

Discharge 8.02E-04 5.34E-04 1.28E-03 1.04E-03 3.52E-04 1.49E-04 Discharge 4.08E-04 3.39E-04 1.15E-03 8.92E-04 1.27E-04 1.19E-04

Losses 51.84% 1.45E-03 79.45% 2.5E-03 24.89% 5.59E-04 Losses 46.34% 6.98E-04 78.60% 1.71E-03 29.26% 1.84E-04

Ipeak + 9.88 6.03 10.83 8.26 6.51 2.82 Ipeak + 7.04 5.11 10.83 11.27 4.31 2.07

Ipeak - -9.06 -7.89 -10.83 -17.65 -5.33 -3.19 Ipeak - -6.15 -6.31 -10.83 -10.89 -2.79 -3.57



105


(Eq. 25)

where, P is the probability, E is the ignition energy, and β0 and β1 are coefficients derived

by Method of Maximum Likelihood [63].

From the ignition results in Table 6.3.0.0.1, the coefficients are derived to be -11.34 and

25669, β0 and β1 respectively. The plot of the ignition result with the probability of

ignition is as shown in Figure 6.2.2.1. Using the probability equation,


(Eq. 25)

N = 8(bcc.deQfggh)(1 + 8(bcc.deQfggh))

Data plots including the probability plot for Figure 6.2.2.1 is in Appendix 10.15.

The results shows 1% probability of ignitions P=0.01, energy to be 0.269mJ, 50%

ignition P=0.5, energy is 0.448mJ and 99% ignition probability at 0.627mJ. A probability

of ignition S-curve is shown with the ignition data, showing the transition zone from

0.269 mJ to 0.627 mJ.



106

Figure 6.3.2.1 Plot of Ignition Results and Ignition Probability Curve for N-

Pentane

Figure shows the plot of ignition results from Table 6.3.0.0.1 and the ignition

probability S-curve for n-pentane

6.3.3 Ignition Discharge characteristics

Average voltage at discharge voltage is 8,483 V for ignited experiments compared to

7,043 V for non ignited experiments. And this trend for larger values in average ignited

experiment verses non ignited experiment is common for initial capacitor energy,

discharger resistor energy, discharge energy, and peak current values.

The effect of lowering capacitor is present and expected in all the analysis as the energy

dissipation or peak current is expected to drop with discharge capacitor value. With

decrease of capacitor value the overall energy for discharge decreases, leading to no

ignition as the energy drop below the minimum ignition energy.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.00E+00 2.00E-04 4.00E-04 6.00E-04 8.00E-04 1.00E-03 1.20E-03

Pro

ba

bil

ity

of

Ign

itio

n,

P

Discharge Energy in joules. J



107

6.4 Material Ignition Discussion

6.4.1 Minimum Ignition Energy

Comparisons made in the current results to Lewis and Moorhouse shows that there is still

a significant amount of knowledge required in order to fully understand the energy

dissipation in the discharges to determine the minimum ignition energy. Attention is also

drawn to Eckhoff’s [14] conclusion on minimum ignition values reported by Lewis to be

unnecessarily conservative [60], which is nearly twice the lowest recorded value. This

experiment calculated 1% probability of ignition of Pentane at 0.269 mJ, 4 percent less

than the 0.28 mJ reported by Lewis. However, a lower value would have been expected as

only energy dissipated at the discharge point is considered, which identifies the

dissipation characteristics in the discharges. The lowest confirmed ignition energy is

0.352 mJ which only represent 33% of the initial energy. The resulting 67% of the initial

energy unaccounted is assumed to have been used to charge other storage elements in the

circuit or dissipated by resistances other than those measured. Since no measurement or

characteristic was done on the stray capacitance, inductance and resistance, there is no

method to identify the energy usage other than at the measured points.

Standardised testing method described by the “ASTM: Standard Test Method for

Minimum Ignition Energy and Quenching Distance in Gaseous Mixtures” [64] was not

implemented in this ignition experiment. Therefore, minimum ignition results can only

act as an indication for the development of the high voltage measurement and ignition

energy experiment for research. It would be for future development to amend this

experiment to the described standardise testing method for the purpose of investigating

the energy dissipation in accordance to defined parameters for testing gaseous mixtures.

6.4.2 Ignition Probability

For a general comparison, Lewis [60] used a 1% probability for the minimum ignition

energy, which gave the reported value of 0.28 mJ at 3.3% volume. Using a 1%

probability this set of ignition results gave a probability of 1% ignition at 0.269mJ. The

low sample count in the ignition results and different experiment setup would be likely

causes of the accuracy in ignition energy at 1% probability. More data and experiment is

required to obtain confident statistically analysed ignition probability results that can be



108

compared with the standardised testing method. More experiments will also reduce the

amount of data point outside the upper region of the s-curve, ignition and non-ignition

respective.

6.4.3 Ignition Discharge

The data from the summarised ignition results is as expected, with respect to the lowering

of energy dissipation when comparing the ignition and no ignition sets. The discharge

voltage varied greatly which was not expected as the same experiment setup is used. The

same gap of 3 mm is maintained which would indicate a fixed potential required for

breakdown and discharge. This volatility in discharged voltage warrants future

investigation where the discharge period can be identified and the respective voltage at

discharge more accurately assessed. A possible reason for the discrepancy in this trend for

discharge voltage could be because at proximity to the transition zone of ignition an extra

600V is required for ignition [65]. Another possible reason is the low data count for the

ignition results.

6.4.4 Capacitance vs. Discharge Energy

A full investigation of the capacitance in relation to the discharge energy was not able to

be completed with the available results. More data are needed to identify the significance

of additional capacitance on the minimum ignition energy. An investigation of

capacitance verse the minimum ignition energy would allow further understanding of the

significance of circuit configuration and the waveform or discharge characteristic, on the

probability of ignition.

6.5 Material Ignition Conclusion

Using the developed experiment method developed in previous investigations, a

systematic experiment for investigating the ignition energy of n-Pentane was conducted.

Through the lowering of ignition energy in the discharge, a lowest ignition value was

established. Collected data was also able to be analysed statically to determine ignition

probabilities at various levels of ignition energies.



109

Lowest ignition energy recorded was 0.352 mJ, and the statically result of 0.269 mJ for 1

% probability of ignition. The results showed close agreement to related published values.


7.0 Contributions and Conclusions

110


The work performed has resulted in the design, fabrication and validation of a system to

characterise the energy in an electric discharge and permits the characterisation of

Minimum Ignition Energy for materials in a well characterised electrostatic discharge.

The following presents a summary of the results and analyses that have been performed

and their associated contributions.

7.1 High Voltage Measurement

The initial assessment that a high voltage electrostatic discharge will be difficult to record

with a high degree of accuracy was proven true. The investigation described in Chapter 3

demonstrated large discrepancies between DC and high frequency response of the

components used to construct a high voltage measurement circuit. This created the need

to fully characterise the components to be used for the discharge measurement with

respect to both DC and high frequency responses. The results showed the rapid decrease

of impedance with respect to high frequency for large resistance and increase of

impedance for current shunts and cables. These effects were explained as high frequency

effects of the stray capacitance decreasing resistance, and the skin effect on the

conductors inducing higher impedance. This resulted in a difference between the

measured value and discharge circuit value during the discharge period. A revised

characteristic of the measurement circuit will need to be identified and used for

experiments as a final step to prevent any additional resistance and capacitance altering

the circuit characteristics. This assessment should include high frequency resultant for

impendence and stray capacitance, for all the connected components including high

voltage measurement points, probes, cables and oscilloscope.

Results from this investigation have identified the importance of carefully characterising

the measurement and experiment circuit. The key characteristics to determine are:

- Resistances at high frequency and the underlining effects of stray capacitance.

Large resistance values are reduced as a high frequency dependant, with

capacitance becoming significant factor in circuit.



111

- Stray capacitance from the handling, connection, design and manufacture of the

resistors and other components produce unwanted stray capacitance at high

frequency. This stray capacitance needs to be accounted for in the final

assessment of the experiment circuit as it cannot be eliminated and will affect the

circuits discharge characteristics.

- Impedance of cabling and current shunts cannot be assumed, as high frequency is

shown to affect the impedance. An assessment must be conducted to determine

the high frequency characteristics of the cabling and current shunts.

7.2 Low Voltage Experiment

In Chapter 5, a low voltage experiment designed for preliminary assessment of the effects

an electrostatic discharge was described, that provided good indication of the energy

dissipation and discharge waveform in a high voltage electrostatic discharge. Discharge

point energy dissipation methodology for the associated energy calculation was

implemented. Due to the simplicity of the circuit it was possible to measure the node

before and after the discharge point, allowing a potential difference to be derived from

two independent voltage measurements. Energy dissipations from all significant

components were able to be calculated from the two voltage measurement as well as their

dissipation in respect to initial energy in the capacitor.

The two energy dissipations calculated from the measurements are 1) the discharge

resistor dissipation and 2) the discharge point dissipation. The initial energy is calculated

from the capacitor and, with a lossless simulation, there should be no unaccounted energy

when the two energy dissipations from the initial energy are considered. However, from

the results obtained there is 5-10% of energy unaccounted, with 5-10% dissipated by the

discharge point and 80-90% dissipated by the discharge resistor. The unaccounted energy

is small but significant when compared to the energy dissipated at the discharge point,

indicating a similar overall resistance value. As for the large 80-90% energy dissipation

by the discharge resistor; this is expected since the experiment does not involve actually

arcing to ground and thus the majority of the energy is dissipated through the components

in the circuit.



112

Current waveforms from the simulated discharges were also evaluated for their peak

current in order to determine energy dissipation. High peak current induced large

instantaneous energy dissipation at the initial peak discharge period, as a result of the

influx of current due to discharge. This period was short at a few nano-seconds and

comparatively short when compared to the overall discharge period.

This investigation reiterates the importance of this energy dissipation calculation for

ignition energy work, as the energy dissipated in the discharge would never be the initial

capacitive energy since components in the circuit and stray resistances will always

dissipate a significant amount of the energy.

7.3 High Voltage Experiment

A high voltage experiment was used to develop a method of measuring and calculating

the ignition energy was described in Chapter 6. Using the theory developed in Chapter 3,

a measurement circuit for high voltage measurement was designed and constructed. Final

characterisation of the measurement circuit found the initial DC response to be vastly

different to the high frequency response. This phenomenon meant energy calculations

could only be conducted in a distinct period of the discharge. Energy calculations were

done from the first point of the fast transient and continued up to 200 nS into the

discharge. It was assumed that the majority of the energy in the discharge was dissipated

by 200 nS. Prior to this time the discharge voltage was recorded for the calculation of the

initial capacitive energy present.

Captured waveforms indicated a significant amount of inductance in the circuit that added

ringing oscillations to the current and voltage waveforms. Further analysis concluded that

95 nH of inductance was induced by components at high frequency which are present

despite limitation of the inductance in design and component selection phase. Analysis

also found that critical damping was achieved with a resistance of 60Ω, indicating that the

resistance in the circuit had fallen to below that figure during the high frequency

discharge. This lack of resistance is indicated in the discharge resistor high frequency

response analysis completed in section 3.6.



113

It was found the large attenuation for reducing the high voltage provided insufficient

resolution for precise voltage reading. A measurement error of 3.33% was therefore

added to the resulting voltage readings. Voltage measurements gave an average of 8.9 kV,

which is approximately 81% of high voltage from the power supply. The voltages are

consistent with the expected 3.3 kV per mm breakdown across air and 9-10 kV across the

experiment 3mm gap.

Voltage was used in the analysis to determine the initial energy, through the use of the

capacitive energy equation and assuming all energy in the discharge derived from the

energy stored in the capacitor. Due to the use of voltage prior to discharge the inherent

DC voltage measurement error is carried forward, resulting in a 10% error with the

capacitor energy calculation. On average, 3.97 mJ was present in the capacitor for

discharge.

The current present in the discharge is measured through the use of a current shunt, via

Ohm’s law with the voltage drop across the current shunt. The current is then used to

calculate the energy dissipated in the discharge resistor with an average of -2.81 uJ

recorded... This figure is negative and much lower than the results from the low voltage

experiment, where 80-90% of the initial energy is dissipated by the discharge resistor; this

indicates that at the discharge discharger resistor is affected by the high frequency of

discharge and has idyllically performed as a storage element as either or both inductive

and capacitive capacity.

By using the current in the discharge, the potential difference at the discharge point was

found from the voltage at the capacitor and the voltage drop over the discharge resistor.

An average of 1.03 mJ was recorded, approximately 26% of the average initial energy.

This figure is much higher than the results from the low voltage experiment, where only

5-10% of the initial energy is dissipated. This increase is thought to be due to the actual

breakdown where electrical energy is converted to heat and light, and due to the influence

of peak current on the energy dissipation. Since the peak current in the discharge

dissipated a large amount of energy during the initial breakdown, when effective

impedance across the discharge point approaches 0 Ω from ∞ Ω.



114

The unaccounted for energy remains after energy dissipated by the discharge resistor and

discharge point has been taken into account comes to 2.12 mJ, representing 54% of the

average initial energy. As was present in the low voltage experiment, there is a noticeable

amount of unaccounted for energy that can’t be discounted as measurement error. The

significance of this energy is apparent as it contains up to 54% of the initial energy and is

not counted toward energy dissipation in the circuit. The unaccounted for energy cannot

be estimated, it can only be deduced when energy dissipation has been analysed. This

energy is assumed to have been utilized to charge other storage element in the discharge

path, for example stray capacitance and inductance not measured or assessed.

Unaccounted energy could also be dissipated by stray resistance or storage till after

discharge where they then are used to charge the discharge capacitor again.

This investigation has developed an important and validated test method for measuring

ignition energies in a high voltage discharge simulating an electrostatic discharge. The

robust measurement methodology allows the calculation of the energy dissipated

throughout the circuit and thus characterises the energy in the discharge. Characterisation

done from the analysis of the data enables the particular properties of interest to be

defined and determined.

7.4 Material Ignition Experiment

Using the method of calculating energy dissipation in a high voltage discharge developed

in Chapter 6, materials ignition experiments to find the ignition energy for n-pentane were

conducted. A series of experiments with different capacitors to deliver different amount

of energy were conducted to determine the minimum ignition energy. The lowest ignited

energy recorded was 0.352 mJ which is in good agreement with the results from Calcote

[61] after considering unaccounted energy losses, and also in good agreement with the

value stated by Lewis [60]. The results of Lewis are for 1% probability of ignition by

Lewis is 4 percent under at 0.269mJ.

In comparison, the statistical analysis of the data by logistic regression predicted ignition

energy of 0.269 mJ at 1% probability of ignition. This is a good indication of the

functionality of the system but should not be accepted for comparison as the experiment

was not conducted in accordance with any standardised methodologies such as ASTM



115

International. Testing consistency with ASTM Int. standards for gases and vapour would

be a valuable further study.

The analysis of the ignition data identified an interesting point that also warrants further

investigation. This was that the discharge voltage for successful ignitions, as compared to

unsuccessful ignitions, showed an increase of 600 V. This difference is unexpected as the

same gap for discharge and experiment setup was present. This difference could be due to

the insufficient amount of data for full statistical analysis, or it could be due to the large

measurement error of the DC voltage measurement. Further tests are required to identify

the cause of this.

Utilizing the developed experimental system and methodology to calculate energy in the

discharge, the ignition characteristics of n-pentane have been explored. A minimum

ignition energy and probability of ignition was obtained from the ignition experiments.

Comparison to related work show agreement to published values. Future work should be

done to calculate solid, liquid and gases minimum ignition energy for a wide range of

materials.

Further investigation is required to obtain a better understanding of how energy other than

the discharge energy is dissipated in the circuit.

7.5 Conclusions

Through this investigation of the characterisation of the minimum energy for ignition in

an electrostatic discharge the following conclusions can be drawn:

- High voltage discharge measurement involving fast transient response will be

difficult to record with a high degree of accuracy. Significant design, assessment

and calibration of the high voltage measurement circuit would be required to

perfect the measurement obtained. This study has shown that this is possible.

- Three key characteristics are required to be assessed for the high voltage

measurement circuit. They are,

o Resistance of the resistors at high frequency.



116

o Stray capacitance from components and connections

o Impedances of the cabling and current shunts used in the circuit that would

be required for the analysis calculations.

- Previous work and the low voltage experiment have reiterated the importance of

energy dissipation in the discharge circuits. Investigation is required as in depth as

possible to determine only the discharge energy.

- Inductance must be limited for a high voltage discharge to prevent oscillatory

ringing in the discharge waveforms. However, it is not possible to eliminate all

inductance.

- Capacitive energy from initial charging is not equal to the ignition energy. From

this experiment data

o Impedance in the circuit will dissipate significant energy, either real or

imaginary when reacted to the high frequency discharge.

o Ignition energy represents approximately 26% of the capacitive energy

o Average 54% of the energy is unaccounted, dissipated by stray capacitance,

inductance and resistance in the circuit.

- Ignition experiment validated the functionality of the high voltage measurement

and ignition energy calculation method.

- N-Pentane ignition energy measurement show close agreement to published value


8.0 Future Work

117

8.0 Future Work

Two potential areas related to this work would benefit from further work.

Firstly, the material ignition experiment in this work should be amended to become

consistent with a standardised methodology for materials ignition test. This would allow

minimum ignition energy results from this measurement methodology to be contributed

to minimum ignition energy data.

Secondly, it would be of significant interest to collate a discharge resistance versus

ignition energy relation to determine a discharge characteristic based on resistance. It has

been shown that a large resistance in the discharge would prevent ignition through the

slow dissipation of energy due to the limited current flow from the large resistance. This

would present as an informative characteristic for a material hazard assessment. A

methodology for investigating this characteristic is required, to make the assessment to

determine if resistance is a significant criterion for ignition.

Similar, a correlation between ignition energies and capacitances of the discharge

capacitor would be of interest. The aim is to investigate the reduced discharge period as

capacitance is decreased with the voltage constant. Also to characterisation of the ignition

energy in relation to the minimum ignition energy, would allow further analysis for

ignition. This work has the methodology developed for this assessment; further work is

required to establish this characteristic as criteria for ignition.

The establishment of a resistance and capacitance relationship of a material for minimum

ignition would allow criteria to be drawn for hazardous analysis for that material. Precise

preventative measures can be deduced from the established correlation, such as placing

additional resistance in ground path or developing imbedded capacitance meter with set

parameters for warning to ignition hazard.


9.0 References

118

9.0 References

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[19] M. J. T. Poopathy Kathirgamanathan, Jurgen Haase, Paul Holdstock, Jan Laperre, Gabriele Schmeer-Lioe, "measurements of incendivity of electrostatic discharge from textiles used in personal protective clothing," Journal of Electrostatics, vol. 49, pp. 51-70, 22/12/1999 1999.

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[21] W. Lobel, "Antistatic mechanism of internally modified synthetics and quality requirements for clothing textiles," presented at the Conference on electrostatic phenomena, St Catherine's College, Oxford, 1987.

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[23] A. N. Z. S. EL/25, "AS/NZS 1020:1995: The control of undesirable static electricity," 1995.

[24] B. S. T. C. PRI-025, "BS7506-1:1995 Methods for Measurements in Electrostatics- part 1: Guide to basic electrostatics," 1995.

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[26] W. D. Greason and G. S. P. Castle, "The Effects of Electrostatic Discharge on Microelectronic Devices - a Review," Ieee Transactions on Industry Applications, vol. 20, pp. 247-252, 1984.

[27] R.K. Eckhoff, "Minimum ignition energy (MIE) - a basic ignition sensitivity parameter in design of intrinsically safe electrical apparatus for explosive dust clouds," Journal of Loss Prevention, vol. 15, pp. 305-310, 2002.

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[45] Sarah Smith, et al., "Electrical arc ignition testing of spacesuit materials," journal of Testing and Evaluation, 2002.

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10.0 Appendix

122

10.0 Appendix

Appendix 10.1 Table of Triboelectric Series

Table of Triboelectric Series [16] Positive Air

Loses Human Skin

Electrons Asbestos

Rabbit Fur

Glass

Human Hair

Mica

Nylon

Wool

Lead

Cat Fur

Silk

Aluminum

Paper

Cotton

Steel

Wood

Lucite

Sealing Wax

Amber

Rubber Balloon

Hard Rubber

Mylar

Nickel

Copper

Silver

UV Resist

Brass

Synthetic Rubber

Gold, Platinum

Sulfur

Acetate, Rayon

Polyester

Celluloid

Polystyrene

Orlon, Acrylic

Cellophane Tape

Polyvinylidene Chloride (Saran)

Polyurethane

Polyethylene

Polypropylene

Polyvinylchloride (Vinyl)

Kel-F (PCTFE)

Gains Silicon

Electrons Teflon

Negative Silicone Rubber


10.0 Appendix

123

Appendix 10.2 Plot of 500MΩ Frequency Response in Linear Magnitude Ω

Plot of 500MΩ Frequency Response in Linear Magnitude Ω

Appendix 10.3 Plot of 200MΩ Frequency Response in Linear Magnitude Ω

Plot of 200MΩ Frequency Response in Linear Magnitude Ω

y = 629797x-0.474

R² = 0.2019

0.00

1,000.00

2,000.00

3,000.00

4,000.00

5,000.00

6,000.00

7,000.00

8,000.00

9,000.00

0.E+00 2.E+08 4.E+08 6.E+08 8.E+08 1.E+09

Lin

ea

r M

ag

nit

ud

e,Ω

Frequency,Hz

y = 1E+06x-0.515

R² = 0.2184

0.00

2,000.00

4,000.00

6,000.00

8,000.00

10,000.00

12,000.00

0.E+00 2.E+08 4.E+08 6.E+08 8.E+08 1.E+09

Lin

ea

r M

ag

nit

ud

e,Ω

Frequency, Hz


10.0 Appendix

124

Appendix 10.4 Plot of 500MΩ Stray Capacitance over Frequency

Plot of 500MΩ Stray Capacitance over Frequency. Mean capacitance is 4.95 pF

Appendix 10.5 Plot of 200MΩ Stray Capacitance over Frequency

Plot of 500MΩ Stray Capacitance over Frequency. Mean capacitance is 5.6 pF

0

2E-12

4E-12

6E-12

8E-12

1E-11

1.2E-11

0.00E+00 2.00E+08 4.00E+08 6.00E+08 8.00E+08 1.00E+09

Ca

pa

cita

nce

, F

Frequency, Hz

Mean=4.95E-12F

0

2E-12

4E-12

6E-12

8E-12

1E-11

1.2E-11

1.4E-11

1.6E-11

1.8E-11

0.00E+00 2.00E+08 4.00E+08 6.00E+08 8.00E+08 1.00E+09

Ca

pa

cita

nce

, F

Frequency, Hz

Mean=5.6E-12


10.0 Appendix

125

Appendix 10.6 Plot of 200MΩ/10pF Capacitance over Frequency

Plot of 200MΩ/10pF Capacitance over Frequency. Mean capacitance is 73.5pF

Appendix 10.7 Plot of 2MΩ/220pF Capacitance over Frequency

Plot of 2MΩ/220pF Capacitance over Frequency. Mean capacitance is 452pF.

0

1E-10

2E-10

3E-10

4E-10

5E-10

6E-10

0.00E+00 2.00E+08 4.00E+08 6.00E+08 8.00E+08 1.00E+09

Ca

pa

cita

nce

, F

Frequency, Hz

Mean=73.50E-12

0.00E+00

2.00E-09

4.00E-09

6.00E-09

8.00E-09

1.00E-08

1.20E-08

1.40E-08

1.60E-08

0.00E+00 2.00E+08 4.00E+08 6.00E+08 8.00E+08 1.00E+09

Ca

pa

cita

nce

, F

Frequency, Hz

Mean=452E-12


10.0 Appendix

126

Appendix 10.8 Simulation and Measurement of Electrostatic Discharge


10.0 Appendix

127


10.0 Appendix

128


10.0 Appendix

129


10.0 Appendix

130


10.0 Appendix

131


10.0 Appendix

132


10.0 Appendix

133


10.0 Appendix

134


10.0 Appendix

135


10.0 Appendix

136


10.0 Appendix

137


10.0 Appendix

138


10.0 Appendix

139

Appendix 10.9 Simulation and Measurement of an Electrostatic Discharge Low Voltage Experiment Results

560k1.5n1.8

k

I II III IV V VI VII VIII IX X Max Min Averag

e

Capacitor 6.57E-07 6.75E-07 6.39E-07 5.23E-07 6.39E-07 5.07E-07 6.37E-07 6.75E-07 6.75E-07 6.57E-07 6.75E-

07

5.07E-

07

6.28E-

07

Resistor 6.21E-07 6.19E-07 6.15E-07 4.66E-07 6.02E-07 4.34E-07 5.96E-07 6.19E-07 6.22E-07 6.15E-07 6.22E-

07

4.34E-

07

5.81E-

07

Switch 6.48E-09 7.26E-09 7.62E-09 4.37E-09 8.76E-09 1.23E-08 1.31E-08 8.6E-09 1.15E-08 7.36E-09 1.31E-

08

4.37E-

09

8.74E-

09

Losses 2.98E-08 4.91E-08 1.67E-08 5.23E-08 2.88E-08 6.08E-08 2.8E-08 4.72E-08 4.15E-08 3.52E-08 6.08E-

08

1.67E-

08

3.89E-

08

% losses 0.04537

6

0.07271 0.02615 0.10015

5

0.04497

9

0.11994

5

0.04399 0.06997

4

0.06144

4

0.05361

2

11.99

%

2.61% 6.38%

Ipeak 0.01784 0.02163

1

0.01761

7

0.01717

1

0.01850

9

0.01672

5

0.01605

6

0.02073

9

0.01940

1

0.02007 2.16E-

02

1.61E-

02

1.86E-

02

560k1.2n1.8

k


e


07

5.46E-

07

5.65E-

07


07

5.10E-

07

5.22E-

07


08

4.97E-

09

8.85E-

09

Losses 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 4.39E-

08

2.59E-

08

3.46E-

08

% losses 5.72E-02 5.97E-02 5.51E-02 7.27E-02 4.75E-02 4.92E-02 4.75E-02 7.00E-02 7.62E-02 7.58E-02 7.62% 4.75% 6.11%


10.0 Appendix

140

Ipeak 0.02051

6

0.02007 0.02051

6

0.01806

3

0.01828

6

0.01672

5

0.01850

9

0.01984

7

0.01850

9

0.01917

8

2.05E-

02

1.67E-

02

1.90E-

02

560k1n1.8k I II III IV V VI VII VIII IX X Max Min Averag

e


07

4.20E-

07

4.40E-

07

Resistor 4.07E-07 3.98E-07 3.97E-07 4.08E-07 3.76E-07 4.1E-07 3.85E-07 4.14E-07 3.88E-07 4E-07 4.14E-

07

3.76E-

07

3.98E-

07


08

5.59E-

09

8.33E-

09


08

1.58E-

08

3.32E-

08

% losses 0.06211

5

0.03757

6

0.06009

2

0.05961 0.13694

7

0.06299

2

0.12665

3

0.06104

7

0.08765

8

0.05681

9

13.69

%

3.76% 7.52%

Ipeak 0.01850

9

0.02163

1

0.01694

8

0.01850

9

0.01694

8

0.02163

1

0.01717

1

0.02185

4

0.02118

5

0.01917

8

2.19E-

02

1.69E-

02

1.94E-

02

560k680p1.8

k


e


07

2.93E-

07

2.97E-

07


07

2.36E-

07

2.55E-

07


09

3.11E-

09

5.45E-

09

Losses 3E-08 3.13E-08 3.48E-08 5.91E-08 3.08E-08 5.73E-08 2.93E-08 3.02E-08 3.12E-08 3.1E-08 5.91E-

08

2.93E-

08

3.65E-

08


10.0 Appendix

141

% losses 0.10252

1

0.10402

6

0.11568

4

0.19641

1

0.10501

3

0.19044

5

0.09991

1

0.10318

5

0.10374

2

0.10577

6

19.64

%

9.99% 12.27%

Ipeak 0.01627

9

0.02073

9

0.01940

1

0.01717

1

0.01784 0.02073

9

0.01806

3

0.01984

7

0.01940

1

0.02163

1

2.16E-

02

1.63E-

02

1.91E-

02

560k470p1.8

k


e

Capacitor 2E-07 1.89E-07 1.89E-07 1.89E-07 1.94E-07 2E-07 1.89E-07 1.89E-07 1.89E-07 2.00E-

07

1.89E-

07

1.73E-

07

Resistor 1.55E-07 1.59E-07 1.77E-07 1.83E-07 1.84E-07 1.86E-07 1.79E-07 1.69E-07 1.78E-07 1.86E-

07

1.55E-

07

1.57E-

07

Switch 2.09E-09 2.78E-09 4.25E-09 3.19E-09 3.42E-09 4.06E-09 2.93E-09 2.82E-09 4.75E-09 4.75E-

09

2.09E-

09

3.03E-

09

Losses 4.25E-08 2.69E-08 7.62E-09 2.73E-09 6.77E-09 9.37E-09 6.69E-09 1.78E-08 6.35E-09 4.25E-

08

2.73E-

09

1.27E-

08

% losses 0.21267

2

0.14245

5

0.04028

4

0.01444

4

0.03480

2

0.04690

5

0.03536

6

0.09403

3

0.03356

3

21.27

%

1.44% 6.55%

Ipeak 0.02073

9

0.02073

9

0.01516

4

0.02140

8

0.02118

5

0.01627

9

0.02118

5

0.02029

3

0.01940

1

2.14E-

02

1.52E-

02

1.76E-

02

560k220p1.8

k


e


08

7.81E-

08

8.51E-

08


08

6.52E-

08

7.95E-

08

Switch 1.53E-09 1.77E-09 1.61E-09 1.67E-09 1.22E-09 9.7E-10 1.78E-09 2.34E-09 1.72E-09 1.72E-09 2.34E- 9.70E- 1.63E-


10.0 Appendix

142

09 10 09

Losses 2.73E-09 2.34E-09 5.49E-10 2E-09 1.09E-08 1.43E-08 2.57E-09 1.71E-09 1.59E-09 9.77E-10 1.43E-

08

5.49E-

10

3.96E-

09

% losses 0.03022

5

0.02744

3

0.00662

7

0.02276 0.12719

5

0.17752

3

0.02840

2

0.02001

6

0.02041

8

0.01145

3

17.75

%

0.66% 4.72%

Ipeak 0.01962

4

0.01984

7

0.01962

4

0.02007 0.01962

4

0.01917

8

0.01917

8

0.01940

1

0.01895

5

0.01984

7

2.01E-

02

1.90E-

02

1.95E-

02

560k1.5n1.5

k


e

Capacitor 6.75E-07 6.57E-07 6.57E-07 6.75E-07 6.75E-07 6.75E-07 6.75E-07 6.75E-07 6.75E-07 6.75E-

07

6.57E-

07

6.04E-

07

Resistor 6.15E-07 6.09E-07 6.2E-07 6.08E-07 6.23E-07 6.14E-07 6.15E-07 5.84E-07 6.15E-07 6.23E-

07

5.84E-

07

5.50E-

07


08

6.44E-

09

1.01E-

08

Losses 5.11E-08 3.97E-08 2.76E-08 4.65E-08 4.38E-08 4.71E-08 4.41E-08 8.41E-08 5.08E-08 8.41E-

08

2.76E-

08

4.35E-

08

% losses 0.07571 0.06049 0.04205

3

0.06887

3

0.06492

5

0.06976 0.06536

7

0.12462

2

0.07527

7

12.46

%

4.21% 6.47%

Ipeak 0.02573

7

0.02252 0.02225

2

0.02118 0.02627

3

0.02010

7

0.02252 0.02654

2

0.02091

2

2.65E-

02

2.01E-

02

2.08E-

02

560k1.2n1.5

k


e


07

5.60E-

07

5.68E-

07


10.0 Appendix

143


07

5.23E-

07

5.27E-

07


08

5.94E-

09

8.57E-

09


08

1.97E-

08

3.27E-

08

% losses 0.04702

6

0.05577

1

0.04670

6

0.04811

5

0.07563

7

0.06436

5

0.07001 0.03517 0.05951

2

0.07127

5

7.56% 3.52% 5.74%

Ipeak 0.02493

3

0.02171

6

0.02546

9

0.02627

3

0.02627

3

0.02037

5

0.02600

5

0.02520

1

0.02305

6

0.02225

2

2.63E-

02

2.04E-

02

2.42E-

02

560k1n1.5k I II III IV V VI VII VIII IX X Max Min Averag

e


07

4.20E-

07

4.42E-

07


07

3.73E-

07

4.01E-

07


08

5.14E-

09

8.05E-

09

Losses 2.77E-08 3.94E-08 2.74E-08 2.46E-08 2.31E-08 5.15E-08 3.11E-08 4.73E-08 3E-08 2.47E-08 5.15E-

08

2.31E-

08

3.27E-

08

% losses 0.06237

6

0.08884

7

0.06174

3

0.05557

5

0.05211

8

0.11929

6

0.07409 0.10385

4

0.06585

5

0.05565

4

11.93

%

5.21% 7.39%

Ipeak 0.02010

7

0.02118 0.02305

6

0.02412

9

0.02627

3

0.02386

1

0.02010

7

0.02520

1

0.02439

7

0.02493

3

2.63E-

02

2.01E-

02

2.33E-

02

560k680p1.5 I II III IV V VI VII VIII IX X Max Min Averag


10.0 Appendix

144

k e


07

2.61E-

07

2.86E-

07


07

2.21E-

07

2.53E-

07


08

4.02E-

09

6.86E-

09

Losses 1.51E-08 2.08E-08 -1.3E-09 3.56E-08 2.62E-08 5.52E-08 3.93E-08 -2.6E-09 3.53E-08 3.54E-08 5.52E-

08

-

2.57E-

09

2.59E-

08

% losses 0.05309

7

0.07301

2

-0.00491 0.12500

6

0.09204

4

0.19371

5

0.12725

4

-0.00981 0.11726

9

0.11762

6

19.37

%

-0.98% 8.84%

Ipeak 0.02118 0.02493

3

0.02520

1

0.02520

1

0.02466

5

0.02198

4

0.02654

2

0.02600

5

0.02010

7

0.02600

5

2.65E-

02

2.01E-

02

2.42E-

02

560k470p1.5

k


e


07

1.79E-

07

1.90E-

07


07

1.58E-

07

1.73E-

07


09

5.42E-

09

6.68E-

09


08

1.09E-

09

1.03E-

08

% losses 0.03647

7

0.02195

2

0.01778

8

0.20003 0.05520

3

0.08124

4

0.00578

9

0.04559

7

0.02059

8

0.04295 20.00

%

0.58% 5.28%

Ipeak 0.02439

7

0.02225

2

0.02466

5

0.02412

9

0.02493

3

0.02546

9

0.02573

7

0.01876

7

0.02573

7

0.01876

7

2.57E-

02

1.88E-

02

2.35E-

02


10.0 Appendix

145

560k220p1.5

k


e

Capacitor 8.29E-08 8.78E-08 8.53E-08 8.29E-08 8.28E-08 8.29E-08 8.53E-08 7.57E-08 8.53E-08 8.78E-

08

7.57E-

08

7.51E-

08

Resistor 8.06E-08 8.3E-08 8.23E-08 8.25E-08 7.68E-08 8E-08 8.13E-08 7.45E-08 8.13E-08 8.30E-

08

7.45E-

08

7.22E-

08


09

3.09E-

09

3.16E-

09

Losses -8.2E-10 1.34E-09 -9.3E-10 -4E-09 2.53E-09 -5.4E-10 9.23E-10 -1.9E-09 5.34E-10 2.53E-

09

-

3.98E-

09

-2.88E-

10

% losses -0.00993 0.01530

1

-0.0109 -0.04803 0.03050

2

-0.00656 0.01081

6

-0.02547 0.00625

8

3.05% -4.80% -0.38%

Ipeak 0.02412

9

0.02412

9

0.02225

2

0.02037

5

0.01903

5

0.02386

1

0.02412

9

0.02278

8

0.02386

1

2.41E-

02

1.90E-

02

2.05E-

02

560k1.5n1k I II III IV V VI VII VIII IX X Max Min Averag

e


07

6.69E-

07

6.76E-

07


07

6.06E-

07

6.24E-

07


08

1.28E-

08

1.65E-

08


08

2.51E-

08

3.55E-

08

% losses 0.03717

7

0.04138

9

0.06422

9

0.04169

5

0.04233

3

0.04120

7

0.05952

5

0.06921

9

0.05584

1

0.07257

4

7.26% 3.72% 5.25%


10.0 Appendix

146

Ipeak 0.03518

2

0.03785

9

0.03021 0.03556

4

0.03365

2

0.03709

4

0.03747

6

0.03059

3

0.03594

6

0.03021 3.79E-

02

3.02E-

02

3.44E-

02

560k1.2n1k I II III IV V VI VII VIII IX X Max Min Averag

e


07

5.61E-

07

5.74E-

07


07

4.95E-

07

5.23E-

07


08

1.02E-

08

1.23E-

08


08

2.78E-

08

3.88E-

08

% losses 0.08911

6

0.04962

9

0.05428

1

0.05223

3

0.06560

3

0.06237

3

0.12199 0.06312

3

0.05955

8

0.05713

4

12.20

%

4.96% 6.75%

Ipeak 0.03174 0.03097

5

0.03518

2

0.03288

7

0.03785

9

0.03212

2

0.03403

4

0.03479

9

0.02753

3

0.03059

3

3.79E-

02

2.75E-

02

3.28E-

02

560k1n1k I II III IV V VI VII VIII IX X Max Min Averag

e


07

4.20E-

07

4.47E-

07


07

3.53E-

07

3.97E-

07


08

7.65E-

09

9.51E-

09

Losses 6.83E-08 2.48E-08 2.88E-08 6.27E-08 3.84E-08 3.46E-08 2.69E-08 5.95E-08 3.28E-08 2.96E-08 6.83E- 2.48E- 4.06E-


10.0 Appendix

147

08 08 08

% losses 0.15407

8

0.05602

5

0.06489

5

0.13759

9

0.08430

7

0.07594

6

0.05906

1

0.14180

3

0.07195

6

0.06685

2

15.41

%

5.60% 9.13%

Ipeak 0.03709

4

0.03709

4

0.03097

5

0.02944

6

0.03556

4

0.03785

9

0.03709

4

0.03594

6

0.03747

6

0.03556

4

3.79E-

02

2.94E-

02

3.54E-

02

560k680p1k I II III IV V VI VII VIII IX X Max Min Averag

e


07

2.93E-

07

2.99E-

07


07

2.19E-

07

2.47E-

07


09

6.97E-

09

8.26E-

09


08

3.19E-

08

4.31E-

08

% losses 0.11256

9

0.10892

5

0.11411

6

0.23420

5

0.11335

6

0.11343

3

0.12308

8

0.15735

4

0.24830

9

0.11705

1

24.83

%

10.89

%

14.42%

Ipeak 0.03785

9

0.03671

1

0.03671

1

0.03671

1

0.03632

9

0.03709

4

0.03747

6

0.03709

4

0.03671

1

0.03747

6

3.79E-

02

3.63E-

02

3.70E-

02


e


07

1.89E-

07

1.91E-

07


07

1.66E-

07

1.78E-

07


10.0 Appendix

148


09

5.74E-

09

6.53E-

09


08

2.27E-

09

6.25E-

09

% losses 0.03975

3

0.01333

8

0.02180

7

0.02936

9

0.08761

5

0.03908

9

0.01203 0.03391

5

0.03489

5

0.01465

3

8.76% 1.20% 3.26%

Ipeak 0.02944

6

0.03632

9

0.03632

9

0.03632

9

0.03632

9

0.03671

1

0.03632

9

0.03594

6

0.02791

6

0.03632

9

3.67E-

02

2.79E-

02

3.48E-

02


e


08

8.29E-

08

8.61E-

08


08

7.22E-

08

7.88E-

08

Switch 3.01E-09 3.13E-09 3E-09 3.1E-09 3.1E-09 3E-09 3.71E-09 4.48E-09 3.1E-09 3.32E-09 4.48E-

09

3.00E-

09

3.29E-

09


09

6.38E-

10

4.01E-

09

% losses 0.02591

8

0.01307

1

0.09437

9

0.01867

8

0.11388

3

0.09288 0.03109

7

0.02376

1

0.00748

1

0.04706

2

11.39

%

0.75% 4.68%

Ipeak 0.03327 0.03441

7

0.03288

7

0.03441

7

0.03327 0.03288

7

0.03097

5

0.02447

4

0.03403

4

0.03441

7

3.44E-

02

2.45E-

02

3.25E-

02

560k1.5n330 I II III IV V VI VII VIII IX X Max Min Averag

e

Capacitor 6.75E-07 6.75E-07 6.75E-07 6.93E-07 6.75E-07 6.75E-07 6.75E-07 6.39E-07 6.75E-07 6.75E-07 6.93E- 6.39E- 6.73E-


10.0 Appendix

149

07 07 07


07

5.78E-

07

6.06E-

07


08

1.96E-

08

2.40E-

08


08

3.59E-

08

4.33E-

08

% losses 0.06196

9

0.06713

3

0.06715

1

0.07382

8

0.06160

3

0.06395

1

0.06316

4

0.05615

7

0.06083 0.06623

7

7.38% 5.62% 6.42%

Ipeak 0.11638

6

0.11516

1

0.11638

6

0.11516

1

0.11271

1

0.11516

1

0.11516

1

0.11026 0.11638

6

0.11516

1

1.16E-

01

1.10E-

01

1.15E-

01

560k1.2n330 I II III IV V VI VII VIII IX X Max Min Averag

e


07

5.46E-

07

5.71E-

07


07

4.92E-

07

5.06E-

07


08

1.91E-

08

2.23E-

08

Losses 4.06E-08 4E-08 4.81E-08 4.01E-08 5.65E-08 4.43E-08 1.81E-08 6.39E-08 5.72E-08 2.67E-08 6.39E-

08

1.81E-

08

4.36E-

08

% losses 0.07043

6

0.06951

5

0.08352

6

0.06958

4

0.09809

9

0.07692

8

0.03321

7

0.11098

8

0.09934

4

0.04761

7

11.10

%

3.32% 7.59%

Ipeak 0.11393

6

0.11393

6

0.11516

1

0.11516

1

0.11393

6

0.11638

6

0.11393

6

0.11393

6

0.10658

5

0.08820

8

1.16E-

01

8.82E-

02

1.11E-

01


10.0 Appendix

150

560k1n330 I II III IV V VI VII VIII IX X Max Min Averag

e


07

4.31E-

07

4.51E-

07

Resistor 3.76E-07 3.95E-07 4.04E-07 4.01E-07 3.99E-07 4E-07 4.06E-07 4E-07 4.02E-07 4.02E-07 4.06E-

07

3.76E-

07

3.99E-

07


08

1.42E-

08

1.74E-

08


08

1.42E-

08

3.47E-

08

% losses 0.12623 0.09611

4

0.07955

2

0.05335

4

0.08453

8

0.08214 0.0534 0.03290

9

0.07895

1

0.07908

2

12.62

%

3.29% 7.66%

Ipeak 0.08330

8

0.11271

1

0.11516

1

0.10291 0.11271

1

0.11393

6

0.11393

6

0.11271

1

0.11393

6

0.11393

6

1.15E-

01

8.33E-

02

1.10E-

01

560k680p33

0


e


07

2.85E-

07

2.99E-

07


07

2.29E-

07

2.43E-

07


08

9.31E-

09

1.10E-

08

Losses 4.14E-08 3.75E-08 4.32E-08 6.1E-08 4E-08 4.06E-08 4E-08 4.95E-08 3.93E-08 5.73E-08 6.10E-

08

3.75E-

08

4.50E-

08

% losses 0.13754

1

0.13144

5

0.14350

4

0.20265

2

0.13286

4

0.13493

6

0.13661

6

0.16003

8

0.13405

6

0.19044 20.27

%

13.14

%

15.04%

Ipeak 0.11393

6

0.11026 0.11393

6

0.11148

5

0.11393

6

0.11393

6

0.11026 0.11393

6

0.11148

5

0.08453

3

1.14E-

01

8.45E-

02

1.10E-

01


10.0 Appendix

151

560k470p33

0


e


07

1.84E-

07

1.91E-

07


07

1.69E-

07

1.76E-

07

Switch 7.09E-09 8.29E-09 7.81E-09 7.3E-09 8.57E-09 8.52E-09 8.43E-09 7.37E-09 9.07E-09 8E-09 9.07E-

09

7.09E-

09

8.05E-

09


08

1.93E-

09

7.16E-

09

% losses 0.01830

6

0.04137

1

0.02553

3

0.07541

8

0.01020

8

0.03726

8

0.02644

9

0.02080

3

0.03238

1

0.08511

5

8.51% 1.02% 3.73%

Ipeak 0.10903

5

0.10536 0.10903

5

0.11026 0.10781 0.10413

5

0.10168

5

0.11026 0.09310

9

0.10781 1.10E-

01

9.31E-

02

1.06E-

01

560k220p33

0


e


08

8.04E-

08

8.56E-

08


08

7.17E-

08

7.79E-

08


09

2.36E-

09

3.02E-

09

Losses 5.43E-10 1.05E-08 -6.61E-

10

3.99E-09 1.15E-08 9.90E-09 7.12E-09 -2.87E-

10

1.01E-09 2.74E-09 1.15E-

08

-

6.61E-

10

4.63E-

09

% losses 0.67% 12.28% -0.78% 4.42% 13.07% 11.60% 8.11% -0.34% 1.25% 3.12% 13.07

%

-0.78% 5.34%


10.0 Appendix

152

Ipeak 9.92E-02 9.92E-02 1.04E-01 1.03E-01 1.02E-01 1.02E-01 1.02E-01 1.00E-01 9.80E-02 1.02E-01 1.04E-

01

9.80E-

02

1.01E-

01


10.0 Appendix

153

Appendix 10.10 High Voltage Experiment Setup

Photo of High Voltage Experiment Setup, Img_2595.jpg

HV Power Supply

HV Return

HV output

Discharge circuit


10.0 Appendix

154

Appendix 10.11 High Voltage Experiment Discharge Point

Photo of the Discharge Point, Img_2596.jpg

HV Return

HV output

Discharge electrodes


10.0 Appendix

155

Appendix 10.12 High Voltage Experiment Measurement Equipment

Photo of the Measurement Equipment, Img_2597

Oscilloscope Tektronix DPO 4034

DC Power supply 30VDC


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Appendix 10.13 Ignition Experiment, Ignition Frame Extract from High Speed

Camera


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Pictures of ignition extracted from high speed camera video


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Appendix 10.14 Table of Ignition and No Ignition Results

100pF(98pF) 275 276 277 278 279 280 281 282 283 284 285 292 293 295 296

Voltage at discharge8804 12325.6 12325.6 10564.8 10564.8 10564.8 8804 8804 8804 8804 8804 7043.2 8804 7043.2 8804

Capacitor 3.80E-03 7.44E-03 7.44E-03 5.47E-03 5.47E-03 5.47E-03 3.80E-03 3.80E-03 3.80E-03 3.80E-03 3.80E-03 0.002431 3.80E-03 2.43E-03 3.80E-03

Resistor 1.25E-03 2.84E-03 3.04E-03 1.66E-03 1.66E-03 1.58E-03 1.22E-03 1.45E-03 1.43E-03 1.25E-03 7.93E-04 6.30E-04 1.01E-03 6.81E-04 1.04E-03

Discharge + 9.17E-04 1.71E-03 1.70E-03 1.79E-03 1.87E-03 1.80E-03 7.66E-04 1.16E-03 1.13E-03 6.06E-04 6.34E-04 3.61E-04 1.30E-03 6.94E-04 1.44E-03

Discharge - -1.05E-03 -2.34E-03 -2.54E-03 -1.24E-03 -1.24E-03 -1.17E-03 -1.01E-03 -1.11E-03 -1.11E-03 -1.06E-03 -6.27E-04 -5.29E-04 -7.37E-04 -5.30E-04 -7.08E-04

1.96E-03 4.06E-03 4.24E-03 3.04E-03 3.11E-03 2.98E-03 1.78E-03 2.27E-03 2.24E-03 1.66E-03 1.26E-03 8.90E-04 2.03E-03 1.22E-03 2.14E-03

Losses 5.84E-04 5.48E-04 1.69E-04 7.76E-04 7.00E-04 9.18E-04 8.01E-04 8.26E-05 1.25E-04 8.88E-04 1.74E-03 9.11E-04 7.49E-04 5.26E-04 6.15E-04

Losses % 15.38% 7.36% 2.27% 14.19% 12.80% 16.78% 21.10% 2.17% 3.29% 23.38% 45.93% 37.46% 19.72% 21.63% 16.20%

Ipeak + 12.44 12.74 12.73592 12.73592 12.73592 12.73592 11.74129 10.94527 11.8408 11.04478 11.14428 7.66 12.73592 10.34826 12.73592

Ipeak - -11.24 -12.74 -12.7359 -12.7359 -12.7359 -12.7359 -8.55721 -12.7359 -12.3383 -9.55224 -8.55721 -7.36318 -12.7359 -10.6468 -12.7359

72pF(68pF) 331 332 333 334 335 336 337 338 339 340 341

Voltage at discharge8804 10564.8 8804 10564.8 7043.2 8804 7043.2 8804 8804 8804 7043.2

Capacitor 2.64E-03 3.79E-03 2.64E-03 3.79E-03 1.69E-03 2.64E-03 1.69E-03 2.64E-03 2.64E-03 2.64E-03 1.69E-03

Resistor 7.69E-04 1.06E-03 7.86E-04 1.03E-03 2.95E-04 9.99E-04 3.18E-04 1.12E-03 5.68E-04 9.79E-04 3.71E-04

Discharge + 7.58E-04 1.06E-03 6.75E-04 9.85E-04 1.29E-04 3.09E-04 1.66E-04 9.29E-05 6.24E-04 9.31E-04 3.78E-04

Discharge - -5.60E-04 -7.93E-04 -5.80E-04 -7.54E-04 -2.37E-04 -8.17E-04 -2.19E-04 -9.70E-04 -3.63E-04 -7.05E-04 -2.49E-04

1.32E-03 1.85E-03 1.25E-03 1.74E-03 3.65E-04 1.13E-03 3.85E-04 1.06E-03 9.87E-04 1.64E-03 6.27E-04

Losses 5.48E-04 8.89E-04 5.95E-04 1.02E-03 1.03E-03 5.11E-04 9.83E-04 4.55E-04 1.08E-03 2.08E-05 6.88E-04

Losses % 20.81% 23.42% 22.58% 26.94% 60.83% 19.40% 58.31% 17.27% 41.00% 0.79% 40.79%

Ipeak + 11.54229 12.73592 10.84577 12.73592 5.074627 7.263682 5.074627 4.378109 11.44279 12.73592 8.258706

Ipeak - -11.8408 -12.7359 -9.55224 -12.1393 -3.8806 -5.97015 -3.48259 -3.28358 -9.45274 -11.8408 -8.25871


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60pF(58pF) 352 353 354 355 356 357 358 359 360 361 362 363

Voltage at discharge7043.2 7043.2 8804 8804 8804 12325.6 12325.6 8804 8804 8804 8804 8804

Capacitor 1.44E-03 1.44E-03 2.25E-03 2.25E-03 2.25E-03 4.41E-03 4.41E-03 2.25E-03 2.25E-03 2.25E-03 2.25E-03 2.25E-03

Resistor 5.16E-04 4.58E-04 5.56E-04 8.62E-04 8.74E-04 1.23E-03 1.34E-03 3.23E-04 4.79E-04 4.95E-04 5.08E-04 4.62E-04

Discharge + 3.51E-04 2.98E-04 7.29E-04 3.92E-04 3.81E-04 1.37E-03 9.86E-04 1.20E-04 1.22E-03 9.40E-04 1.11E-03 9.58E-04

Discharge - -3.55E-04 -3.22E-04 -3.75E-04 -6.63E-04 -6.87E-04 -8.82E-04 -1.00E-03 -2.44E-04 -2.38E-04 -2.71E-04 -2.49E-04 -2.37E-04

7.06E-04 6.20E-04 1.10E-03 1.05E-03 1.07E-03 2.25E-03 1.99E-03 3.64E-04 1.45E-03 1.21E-03 1.36E-03 1.20E-03

Losses 2.16E-04 3.61E-04 5.88E-04 3.32E-04 3.06E-04 9.25E-04 1.08E-03 1.56E-03 3.14E-04 5.42E-04 3.83E-04 5.90E-04

Losses % 15.01% 25.09% 26.15% 14.76% 13.62% 20.99% 24.54% 69.43% 13.95% 24.12% 17.04% 26.26%

Ipeak + 7.263682 8.159204 11.54229 8.059701 7.661692 12.73592 12.73592 4.278607 12.73592 12.73592 12.73592 12.73592

Ipeak - -9.05473 -6.46766 -11.9403 -8.1592 -7.9602 -12.7359 -10.6468 -3.9801 -12.7359 -11.1443 -11.9403 -9.35323

50pF(45pF) 307 309 310 311 312 313 316 317 318 319 320

Voltage at discharge8804 7043.2 7043.2 5282.4 7043.2 7043.2 7043.2 10564.8 7043.2 12325.6 12325.6

Capacitor 1.74E-03 1.12E-03 1.12E-03 6.28E-04 1.12E-03 1.12E-03 1.12E-03 2.51E-03 1.12E-03 3.42E-03 3.42E-03

Resistor 5.91E-04 3.45E-04 2.00E-04 1.41E-04 4.13E-04 2.95E-04 3.38E-04 6.88E-04 3.86E-04 8.07E-04 8.57E-04

Discharge + 6.74E-04 3.14E-04 6.06E-04 2.84E-04 2.29E-04 2.81E-04 3.59E-04 8.79E-04 3.77E-04 1.18E-03 1.16E-03

Discharge - -4.30E-04 -2.54E-04 -8.44E-05 -8.32E-05 -2.83E-04 -2.10E-04 -2.14E-04 -4.44E-04 -2.41E-04 -5.00E-04 -5.52E-04

1.10E-03 5.68E-04 6.90E-04 3.67E-04 5.13E-04 4.91E-04 5.73E-04 1.32E-03 6.18E-04 1.69E-03 1.71E-03

Losses 4.86E-05 2.03E-04 2.26E-04 1.20E-04 1.90E-04 3.30E-04 2.05E-04 5.00E-04 1.12E-04 9.27E-04 8.48E-04

Losses % 2.79% 18.19% 20.28% 19.04% 17.02% 29.58% 18.33% 19.91% 10.05% 27.11% 24.80%

Ipeak + 11.24378 6.865672 10.84577 6.169154 5.472637 7.661692 8.457711 12.1393 9.054726 12.73592 12.73592

Ipeak - -11.4428 -8.0597 -10.2488 -7.56219 -5.37313 -5.47264 -5.47264 -11.9403 -6.26866 -12.7359 -12.7359


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162

Appendix 10.15 Data for Ignition Probability Plot, with Ignition Data

B0 -11.5038

B1 25660

Energy Probability

0 1.01E-05

0.00005 3.64E-05

0.0001 0.000131

0.00015 0.000474

0.0002 0.001706

0.00025 0.006128

0.0003 0.021757

0.00035 0.074275

0.0004 0.224471

0.00045 0.510798

0.0005 0.790211

0.00055 0.931451

0.0006 0.980007

0.00065 0.994377

0.0007 0.998435

0.00075 0.999566

0.0008 0.99988

0.00085 0.999967

0.0009 0.999991

0.00095 0.999997

0.001 0.999999

0.00105 1

0.0011 1

0.00115 1

0.0012 1

0.00125 1

0.0013 1

0.00135 1

0.0014 1

0.00145 1

0.0015 1

0.00155 1

0.0016 1

0.00165 1

0.0017 1

0.00175 1

0.0018 1

0.00185 1

0.0019 1


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0.00195 1

0.002 1

0.00205 1

0.0021 1

0.00215 1

0.0022 1

0.00225 1

0.0023 1

0.00235 1

0.0024 1

0.00245 1

0.0025 1


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164

Appendix 10.16 Confirmation of Candidature Document, Sections: Concept and Literature

Review


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