modelo de arco electrico

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)

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500 kV Single Phase Reclosing Evaluation Using Simplified

Arc Model Kanchit Ngamsanroaj

1, Suttichai Premrudeepreechacharn

2, Neville R. Watson

3

1,2Department of Electrical Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai 5200, Thailand

3Department of Electrical and Computer Engineering, College of Engineering, University of Canterbury, Christchurch 8140,

New Zealand

Abstract The interaction between a fault arc and power

system has a big influence on the successful reclosing of a

faulted system and hence evaluation of this interaction is very

important. This paper mainly focuses on a proposed

technique of simplified arc model for evaluation of single

phase reclosing scheme for extra high voltage transmission

system. Both primary and secondary arcs behavior have been

simplified and implemented in a custom PSCAD/EMTDC

model as a time-varying resistance. The successful single-

phase reclosing is investigated by conducting fault clearing

and reclosing cases utilizing the simplified arc model. The

illustrative cases are presented in order to determine

approximately the maximum arc duration that may be

expected. To improve the scheme, the shorten pre-set dead

time is investigated. The proposed simplified arc model has

been used to evaluate the studied existing EHV transmission

system for single phase reclosing. By making the pessimistic

assumptions with respect to still air conditions, the more

severe conditions derived from the studied system were

simulated to determine the longest likely extinction times.

Keywords Single phase reclosing; Secondary arc current; Arc model; ElectroMagnetic Transients Program.

I. INTRODUCTION

More than 90 % of all line faults are single phase to

ground type and most of these are transitory. For these

faults, phase-to-ground faults have received the most

attention in system studies. The fault arc will be quenched

and the fault path dielectric will completely restore during

the dead time of the breaker, usually 25 30 cycles (0.5

0.6 s) for 500 kV systems. Three-phase reclosing, however,

may cause system instability and result in system breakup

and outages. For such instances, single phase reclosing

provides an improvement, without causing system

instability, to enhance transmission system availability.

Over the years analog and digital techniques have been

extensively used by the researcher to predict system

performance, but the main difficulty has always been the

arc modeling during the secondary arcing phase with

resultant uncertainty associated with the predictions of

secondary arc extinction times and the empirical rules used

as measures of acceptability and subsequent reclosing.

Auto-enclosing is an efficient tool to compensate the

expected growth in the number of line faults caused by

lightning strokes which is presumable in any compact line

design because of the reduced insulation distances. This is

concluded by L. Prinkler, et al [1 and 2]. A representation

of the secondary arc is essential in determining the auto-

reclosing performance of EHV transmission lines. The

dynamic behavior of the arc is presented as a time-varying

resistance using models feature of the ATP-EMTP

program. It is shown that random variation of the arc

parameters influences significantly the arc extinction time

besides the capacitive and inductive coupling between the

faulty and the sound phases. Parameters for the arc model

have been extracted from staged fault tests records carried

out on a double-circuit uncompensated 400 kV line.

Tavares and Portela [3] studied the importance of

optimizing transmission system parameters from its

conception, considering altogether the relevant options and

possibilities, in order to have better cost-performance

result. The presented results were obtained in the study of a

real transmission system expansion, based on an 865 km

long line. The single-phase auto-reclosing procedure was

one of the aspects carefully studied. The secondary arc

current was mitigated through the traditional solution of

using the neutral reactor on the existing shunt reactor

banks. The method of obtaining the optimized value for the

neutral reactor was discussed. Several system elements

were adjusted to improve the system performance.

Danyek and Handl [4] collected and analyzed several

articles from the international publication about secondary

arcs. They classified the parameters which influenced on

the secondary arc extinction time into two groups. The first

group parameter (line length, rated voltage, method of arc

ignition, degree of compensation, location of shunt reactor

and distance between arcing horn) is influenced by the

network configuration and operation (at field test) or by the

laboratory test circuits. The others (fault location, primary

arc current and duration, wind, secondary arc resistance,

recovery voltage and secondary arc current) are depending

on atmospheric or other stochastic conditions.



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Jamali and Ghaffarzadeh [5] proposes an algorithm for

adaptive single phase auto-reclosing based on processing

the mode current signal using wavelet packet transform,

which can identify transient and permanent faults, as well

as the secondary arc extinction time. The studied method

has been successfully tested under fault conditions on a 500

kV overhead line using EMTP. The algorithm does not

need a case-based threshold level. Its performance is

independent of fault location, line parameters, and pre-fault

line loading conditions.

Many studies have been made based on measurements of

secondary fault current and time for arc extinguishing on

single-circuit and double-circuit lines. Hasibar, et al. [6]

reported the use of high-speed grounding switches. This is

an effective method for extinguishing secondary arc current

associated with single-pole switching. High-speed

grounding switches are connected at each end of BPAs

existing 500 kV transmission line, hence in parallel with

the secondary arc, and will permit rapid circuit breaker

reclosing.

Kappenman, et al. [7] performed fault tests on a 528 km

500 kV single-circuit line. The tests were made at three

different positions along the line. The line had reactive

compensation. Although not specifically stated, it is

expected that the shunt reactors were selected for optimum

or near optimum compensation. The secondary arc current

extinguished very quickly, probably because the line was

well compensated and fault current (If) was low. The slope

of the recovery voltage (R) in the first few ms after the arc

extinguished is very low. It was noted that the time until

extinguishing was mainly dependent upon the DC offset of

the secondary fault current, which was a function of the

breaker opening time.

The results of a large number of single-phase reclosing

experiments on two transmission lines were reported by

Scherer, et al. [8]. The first line was a 243 km 765 kV line

in the United States, and the second was a 417 km 750 kV

line in the USSR. Reactive compensation with the usual

neutral reactor was used on both lines, although various

reactor configurations were used during the tests. Scherer,

et al. indicates that the tests on the 765 kV line with the 4.2

m arc length support a TRV initial rate of rise of 10 kV/ms

for successful extinguishing.

Shperling, et al. [9] presented on test results on the same

243 km 765 kV line as considered in [8]. It was noted that

the arc resistance has a significant effect on the secondary

arc current, with this secondary current had a third

harmonic component of about 40%. It is also stated that the

withstand rate of rise of the 4.2 m gap was about 10 kV/ms,

and also that for this line the rate of rise was around 0.2If .

Based on the results reported above, it would appear that

for a 500 kV system, single pole reclosing schemes have

pre-set delay times (typically 0.4 to 0.5 s) that reclose the

open circuit breaker phase whether the arc has extinguished

or not. Successful reclosing will occur when the secondary

arc self-extinguishes prior to the time of reclosing.

Considering the range of published reference data, the

following values will result in successful reclosing for the

majority of cases:

The secondary arc current is less than 40 A rms.

The rate of the recovery voltage after the arc clears is less than 10 kV/ms.

In order to improve the stability of the system, it is

desirable to restore the service as soon as possible; it is a

common operating practices to reclose a circuit breaker a

few cycles after it has interrupted a fault.

Auto-reclosing provides a means of improving power

transmitting ability and system stability which notes that

many adaptive reclosing algorithms have been proposed at

present. At the same time, the conventional reclosing which

adopts the fixed dead time interval strategy, that is, the

reclosing is activated after a time delay to restore the

system to normal as quickly as possible without regard to

the system conditions. Although these simple techniques

cannot provide the optimal operating performance, the

conventional reclosing scheme is still used in many

utilities. For this reason, in practical point of view, the

simplification of the arc model will be another approach

because of the difficulty of setting up field tests for realistic

representation as indicated in some of the above published

studies. This paper focuses on a proposed technique of

simplified arc model for evaluation of single phase

reclosing scheme for extra high voltage transmission

system. Both primary and secondary arcs behavior were

simplified and implemented in a custom PSCAD/EMTDC

model as a time-varying resistance. Due to highly random

and complex behavior of the secondary arc it is difficult to

reproduce the exact arc duration by digital simulation. This

notes that the simplified arc model is suitable for arcing

fault simulation applications. The model and simulation

results are compared with field test reported in the technical

literature and the published detailed arc model while the

rest of studied system model and associated parameters will

be calibrated with the field test for line energization in

Thailand. The successful single-phase reclosing is

investigated by conducting fault clearing and reclosing

cases utilizing the proposed simplified arc model by using

Thailand 500 kV transmission system between Mae Moh

(MM3) and Tha Ta Ko (TTK) as studied cases.



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The illustrative cases are presented in order to determine

approximately the maximum arc duration that may be

expected. To improve the scheme, the shorten pre-set dead

time is evaluated together with compensation of secondary

arc; the successful reclosing will occur and bring the

system stability back. The proposed simplified arc model

has been used to evaluate the studied existing EHV

transmission system for single phase reclosing. By making

the pessimistic assumptions with respect to still air

conditions, the more severe conditions derived from the

studied system were simulated to determine the longest

likely extinction times.

II. SINGLE PHASE RECLOSING AND ARC CURRENT

A. Single Phase Reclosing

If single phase reclosing is used, then for a single-line

to-ground fault, only the faulted is cleared. After a time

delay the breakers at each line end are cleared. The two

unfaulted lines remain connected, and keep on carrying

around 54 % of the pre-fault power [10 and 11]. With

single phase switching, the energized phases inductively

and capacitively coupled energy into the faulted phase.

This coupled fault current which can sustain the arc. This

coupled fault current is usually called the secondary arc

current. With relatively short transmission lines, the

secondary arc current may be so low that the fault

extinguishes quickly and reclosing can be accomplished

after only a slight delay. With longer lines, some type of

action is needed to reduce the fault current.

After fault inception, the current spurting into the fault

with all there beakers poles closed can be defined as

primary arc current (Ifp) as shown in fig. 1 (a). After the

faulted phase is isolated, the current is sustained due to the

coupling from the other two phases. Due to this coupling,

current will proceed to pour into the fault, by means of

maintaining the arc in a reduced state commonly referred to

as a secondary are current (Ifs) as depicted in fig. 1 (b). As

the arc path is cooled, and probability elongated, a current

zero may be reached where arc extinction will take place.

Even so, the capacitive and inductive coupling also

produces a recovery voltage across the former arc path.

This recovery voltage may be big enough to cause re-

ignitions or restrikes of the fault arc. And finally, after the

arc has quenched, a complete reclosing still depends on the

ability of the switched phase to withstand the transient

voltage at the instant reclosing.

As above explained, the secondary arc current consists

with two currents preserved by electrostatic (Ifc) and

electromagnetic (Ifm) coupling from the two unfaulted

phases [12].

fmfcfs III (1)

Fig. 1 Diagram concept of arc current

The inductive is recognized as the smallest and the

capacitive coupling as the largest contributor to the

secondary arc current. When shunt reactors are present,

these cancel the contribution of the shunt capacitance to the

secondary arc current and the inductive component

increases.

Fig. 2 Electrostatic coupling diagram of a single, symmetrical and

fully transposed line

The calculation of secondary arc current via electrostatic

coupling was developed by IEEE Power System Relaying

Committee Working Group [12]. Fig. 2 illustrates the

system during the pole-open condition after the system

experiences a single-phase-to-ground fault. Fig. 2(a)

depicts the secondary arc for an open phase A. It presents

the capacitive coupling between phases (Ch) and phase to

ground (Cg). The diagram is a representation of a line that

is assumed to be fully transposed. The Thevenin equivalent

circuit derived from fig. 2(a) is shown in fig. 2(b).

The magnitude of Ifc is in direct proportion to the line

voltage and the line length. As shown from fig. 2(b):



4

)2/1

1(

h

thfcCj

VI

(2)

When the line is loaded, there is a component of

secondary arc current induced by the electromagnetic

coupling (Ifm) from the unfaulted phases. The accurate

calculation of Ifm needs transient studies due to the fact that

the induction is the sum of many dynamic variables

involving the line currents flowing in the unfaulted phases,

adjacent line loading, the method of secondary arc

extinction, etc.

The magnitude of the recovery voltage (Vr) is directly

proportional to the line voltage and the relative value of Ch

and Cg. Consequently, Vr does not vary with line length.

According to fig. 2(b), the recovery voltage on phase A

after fault clearing can be approximated by:

)/1()2/1(

/1

gh

g

thrCjCj

CjVV

(3)

B. Arc Current

The single phase reclosing of a typical 500 kV

untransposed line with length of 135 km has been

investigated by the analysis of arc measurement on the arc

tests at FGH in Germany [13 and 14]. The single phase to

ground fault of phase b at the sending end is isolated by

single phase switching. The secondary arc voltage and

current obtained from the simulations are presented in Fig.

3. The arc duration determined from the Fig. 3 is 0.42 s.

The primary fault arc period is considered between fault

inception and clearing at both ends of the faulted phase.

After the transition of primary arc to secondary arc occurs,

it can be observed that the voltage across the arc path is

gradually built-up until the final extinguishment of arc.

Then both end breakers are reclosing consequently which

characteristic offset of the recovery voltage is noticed as

shown in Fig. 3(a). The arc duration determined from the Fig. 3(b) is 0.42 s.

The simplification of Johns, et al. [15] in this study can

be represented according to the principle of thermal

equilibrium for modeling the fault arc. This arc is evaluated

by the following differential equation:

)(1

fifi

fi

figG

Tdt

dg (4)

Fig.3 Simulation of single phase reclosing on 500 kV line [14]

(a)Arc voltage (b) Arc current

The subscript fi presents each phases of the fault arc (fp

for primary arc and fs for secondary arc). Tfi is considered

as the time constant of the arc path, while gfi presents the

time varying arc conductance. The stationary arc

conductance (Gfi) and can be obtained from:

fifi

filV

iG (5)

The stationary arc conductance can be explained as an

arc conductance when the arc current is kept for a fairly

long time under constant external conditions. The arc

voltage per unit length is defined as Vfi. For the primary

arc, Vfp is constant and given as 15 V / cm when the range

of the peak of the primary current is between 1.4 to 24 kA

[15]. In the other point, Vfs is a function of the peak of the

secondary current (Ifs) in the range of Ifs from 1 A to 55 A.

Vfs can be averaged by Vfs = 75Ifs-0.4

V/cm. Where i is the

absolute value of arc current and lfi presents the arc length

of each phase. The time constant can be determined

according to the rate of rise of the arc voltage from the

following equation:



5

fp

fp

fpl

IT

(6)

)(

4.1

rfs

fs

fstl

IT

(7)

Where the coefficient is about 2.8510-5 for primary arc current and is around 2.51103 for secondary arc

current. Ifi is defined for the peak current.

The probability of secondary arc extinction is considered

by the sustained secondary arc current and the post-fault

recovery voltage. Many published papers have indicated

that a typical secondary arc current for a 500 kV is below

20 A per 161 km. The required breaker dead time is

between 0.25 and 0.4 s. A typical recovery voltage value is

between 10 to 25 % of the live voltage without shunt

reactor compensation. [7 - 9], [11], [12] and [16].

III. DESCRIPTION OF ARC MODEL

The fault arc is very important when studying arc

phenomena such as single-phase reclosing because

reclosing operation must be after secondary arc is

permanently extinguished. The secondary arc is what

happens to highly sophisticated occurrence. Anticipating

the quenching of a second arc is certainly not enough to

make precision impossible with the information and knowledge that is available to date.

In this paper, the arc is simplified and incorporated as a

custom component model in PSCAD/EMTDC. It is based

on a changing resistance for the primary arc and a changing

resistance for the secondary arc and a changing current

source after the transition to secondary arc. The proposed

simplified arc model is considered with the successive

partial arc extinctions and restrikes when the arc current

and voltage pass through zero many times. The permanent

arc extinction will occur when the voltage impressed across

the discharge path is lower than the arc reignition voltage.

The steps for calculating the arc resistance are shown in the

flowchart of fig. 4.

The flowchart consists of calculation of arc conductance,

arc equation and solution. The arc conductance is updated

at each time step of the solution. It consists of an arc

component which effectively modeled both a primary arc

(the high current arc before circuit breakers open) and the

secondary arc which remains after the circuit breakers

open.

It needs to be noted that the simplification indicate the

desirability of performing simulation runs consistent with

relatively low wind speed or zero speed and with initial arc

length of 4 m. in order to determine the worst case

extinction time condition. When interpolation was added to

PSCAD/EMTDC, this component worked satisfactorily for

the secondary arc. In this study, the algorithm of fault arc

modeling from single phase to ground fault based on

simplified model is proposed and simulated. The logic

function and other modules in the PSCAD/EMTDC are

used to accurately establish model of dynamic

characteristics of primary and secondary arc. The initiation

time of fault inception and duration of fault can be set

before simulation of fault at desired location in the studied

system.

Fig. 4 Flowchart of the simplified arc model

http://www.oxforddictionaries.com/definition/english/occurrence#occurrence__3



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The alteration from primary arc to the secondary arc can

be counted from the time of the first current zero in the arc

after which the magnitude of the primary arc decreased

significantly. A Thevenin equivalent of the network seen

by the arc, which can be done by freezing the entire history

in terms of electromagnetic transient solution at each time

step. Once the Thevenin equivalent network has been

considered in the calculation procedure, its characteristics

are superimposed on the secondary arc characteristic. And

at the intersection, the arc current is defined robustly. The

network solutions are re-calculated with the resolved arc

current comprised as a current source.

For verifying of the model, validation test needed to be

considered. The comparisons between field tests and

simulations are another direct way that directly to verify the

representations. But field tests require resources and

network outages which may affect the reliability of system

Moreover, in some field tests could not be able to perform

because of operational limitations. To get more confidence

with proposed model, the comparison with published

computed result or detailed arc model [19].

In this paper, the simplified arc model has been

investigated with a good record of the field test from

published detailed arc model [13 and 14] while the rest of

studied system models and associated parameters are

calibrated with the field test for line energization.

A. Verification with published detailed arc model

The proposed simplified arc model is improved with

published detailed arc model. Based on the arc model given

in [14], the former detailed arc model described in [14] has

been improved by the analysis of arc measurements on the

arc tests performed by FGH (Power Research Institute) in

Germany. The secondary arc transients have then been

compared between the proposed simplified arc model and

detailed arc model from [14] and using the same network

configuration of 500 kV untransposed line with length of

135 km. as in the published detailed arc model. The

secondary arc voltage and current obtained by the proposed

arc model are given in Fig. 5. By means of comparison

between Fig. 3 and Fig. 5, the influence of arc parameters

on arc duration and arc length at the moment of extinction

is shown. The elongations of the arc and time variation of

arc time constant depending on arc length are the major

factors in this respect. The arc extinction is the most

difficult phenomenon of the secondary arc to define. The

arc extinction criteria used in the detailed models are

derived and adjusted empirically and have been improved

by means of extensive arc tests on real insulator

arrangements.

It is apparent from Fig. 5 that the nonlinearities in the

fault arc path current manifest itself into significantly

distorting the voltage waveforms in the time period from

breaker opening to final arc extinction. It is noted that the

peaks and trajectories of both voltages and currents in

proposed arc model and detailed arc model are in same

pattern. This ensures the validity of the proposed model.

Fig. 5 Simulation result from the proposed arc model on 500 kV line

from [14]

It, nevertheless, is very hard to have a complete

agreement of the field tests and the simulation cases. From

the comparison it is noted that in general the correspondence of waveforms is reasonably good for

reclosing simulation with following observations:

The simulated primary arc current wave shapes are somewhat similar in agreement with the recorded

primary arc current.

In comparison between actual and simulated cases, the size of the primary arc currents and the recovery

voltages are not always close in the peak value.

For the published detail case, the duration of the secondary arc extinction time was similar to or less

than the simulated case.

Although the simulated results on secondary arc

extinction times are concurring but not precise, the

differences can be attributed to modeling accuracy and

imprecision of data. For published detailed test, the system

equivalents at each end of the line are not known exactly.



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B. Calibration for studied system model components with field test

The rest of the studied system components and

associated parameters such as transmission lines,

transformers, generating sources, circuit breakers, surge

arrestors and shunt reactors are calibrated with field test for

line energization. For validating the studied system model

components, the comparisons between simulation and field

tests are also used.

Fig. 7 Simplified arc model for fault arc at the fault location

Due to the limitation of system availability and stability,

the scope of field tests was defined to line energization

with all protection. During the simulation, recorded field

tests results are used to calibrate the system model

components and associated parameters. The accuracy of the

model of the system as shown in Fig. 6 can be verified by

field tests from the studied system. The receiving end

voltage waveform during the field tests were recorded and

compared with the corresponding simulation results [18

and 19].

Fig. 7 depicts the comparison results between field test

record and simulation test for the case of MM3 TTK

circuit no. 2 which is one of many tests. TTK was he

receiving end for each test while the rest of the system was

in service. The simulation was configured as the field test

configuration. The voltage waveforms are nearly similar.

The comparisons give satisfactory results to confirm the

validity of the simulation model components and

parameters used [7], and [20 - 23].

The almost random variation of arc parameters

influences significantly the arc performance during single

phase reclosing on transmission lines. Whereas the primary

arc presents generally a deterministic behaviour as

observed at field and laboratory tests [13 and 14], the

secondary arc has extremely random characteristic affected

by external conditions around the arc channel like ionized

surrounding air, wind, thermal buoyancy and

electrodynamic force. Due to highly random and complex

behaviour of the fault arc, it is almost impossible to

reproduce the exact arc duration by digital simulations.

However, the proposed simplified arc model has been

evaluated and can employed to determine maximum dead

times (worst case) and to evaluate the performance of arc

suppression schemes in single phase reclosing studies. This

is point to the essential for this work.

Fig. 7 The comparison of field test (a) and the simulation results (b)

The validation tests for the proposed simplified arc

model and transmission line system components from the

above ensure the accuracy of representation for this study.

The proposed fault arc, transmission line and system

component models are used to study secondary arc

extinction times for single phase reclosing after single line

to ground fault in an EHV line.

IV. SYSTEM MODELING

The system adopted for simulation represents the three

500 kV lines from Mae Moh (MM3) to Tha Ta Ko (TTK),

as shown in fig. 7, which is the longest transmission line

section (about 330 km for each line) in Thailand.



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The simulation study is conducted to determine the form

of single-phase reclosing using simplified arc model

occurring after single-line-to-ground fault in different

locations. The PSCAD/EMTDC software is incorporated in

the study. The 500 kV circuits in the network have been

modelled using the frequency dependent model [23].

According to the studied system, the 500 kV interconnected

between MM3 and TTK substation comprises three

circuits:

Single circuit 500 kV MM3 TTK, using 4x795 MCM ACSR/GA conductors per phase, 325.675 km, with

3x90 MVAr/525 kV line shunt reactor at both ends.

Double circuits 500 kV MM3 TTK, using 4x795 MCM ACSR conductors per phase, 334.855 km, with

3x110 MVAr/525 kV line shunt reactor at both ends.

The parameters of the line are calculated based on the

conductor sizes and their geometric spacing on the

transmission towers. All effects of inductive and capacitive

coupling between each phases of particular circuit, and

coupling between circuits on the same transmission tower

are therefore included in the network model. Phase

transposition and fixed compensating reactors are

represented. Each transformer and auto-transformer will be

modeled in detail with available information: MVA rating,

winding voltage and configuration, tap change ranges and

normal setting, and leakage reactance between windings. The generators in the network are represented using a 3-

phase AC voltage source, with specified source and/or

zero-sequence impedance. The locations of the circuit

breakers that will be switched are associated on the studied

system. Other parameters of the circuit breakers are

considered: protection delay or clearing times, reclosing

sequences, mechanical closing time and variation in pole

closing times, and closing resister. The location and rating

of installed surge arresters are included. At the boundary of

the simulation, the external grid or the remaining parts of

500 kV network are represented by a voltage source

connected with driving impedance for the feeding network.

For simulation of the fault, the simplified arc model is

applied. The proposed fault can be represented by time

varying resistance model during primary arc period and for

secondary arc until self-extinguish occurs, as previously

described. The arc model will present the successive partial

arc extinctions and restrikes when arc current and voltage

pass through zero many times. The permanent arc

extinction will occur when the voltage impressed across the

discharge path lower than the arc reignition voltage. The

developed custom model for the arc is used at the fault

location as shown in Fig. 6. The investigation is conducted

at no load on the system.

The factors considered to have the most influence on

arcs are the duration and magnitudes of the primary arc

currents, the fault location, wind and humidity conditions,

and line power flow. From the test results in [7], no

correlation can be determined of the effect of primary arc

magnitude and duration as well as fault location upon

secondary arc extinction time. Also no correlation could be

found linking the pre-fault power flow on the line to

secondary arc extinction time. Wind speed may have some

subtle effects upon the secondary arc extinction time. It

needs to be emphasized that the considerations indicate the

desirability of performing simulation runs consistent with

relatively low wind speed or zero speed and with initial arc

length of 4 m. in order to determine the worst case

extinction times.

V. RESULTS

Having developed the proposed simplified arc model, it

was decided to utilize the digital simulation to evaluate the

studied existing EHV transmission system. By making the

pessimistic assumptions with respect to still air conditions,

the more severe conditions derived from the studied system

were simulated using EMTP to determine the longest likely

extinction times. For the 500 kV circuit MM3 TTK#1,

the studied system is considered to be at steady-state

operating condition prior to the inception of a phase-to-

ground fault on phase A at time 0.25 s (T1). The sending

end phase A breaker clears at time 0.5 s (T2), followed by

the opening of the receiving end breaker at time 0.52 s (T3).

The primary arc is taken during the primary arc period (T1-

T3). The arc transition is occurred at the time the current in

fault arc path first reached zero, after the receiving end

breaker interrupts current. Actual current interruption is

arranged to occur at the first current zero following contact

separation of breaker pole inquisition. It can be seen that

the voltage exhibits the usual high frequency travelling

wave induced distortion during the primary arc period.

Follow arc transition to secondary arc period at time T3,

there is a gradual build-up of the voltage across the arc

path. Initial oscillations in the secondary arc current are

observed. The source of the oscillation is caused from the

excitation of the natural frequency formed by the fault

points with transmission line. This does not appear to

hinder arc extinction. Considerable high frequency

distortion is observed near final arc extinction, and this is

caused by collapse of voltage across the secondary arc

following sudden restrike. After final extinction of

secondary arc at time 0.604 s (T4), the line is re-energized

by sending end phase breaker closing at time 1.05 s (T5)

and then time 1.07 s (T6) for the receiving end.



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The characteristics of the fault arc, current and voltage at

fault point, throughout the process of single-phase

reclosing are depicted in Fig. 8.

This is also illustrated three distinct stages of

development of the secondary arc; an initial half cycle

period of relatively high noise distortion caused by

travelling wave components traversing the fault point, a

relatively long period during which arc the arc voltage

increases due to the effect of an increase in the arc length,

and a final short pre-extinction period where the arc tries to

extinguish but sudden re-ignition causes current and

voltage spikes to be generated.

Fig. 8 Simulation result for fault arc at the fault location (System

response of Current and Voltage for phase A to ground fault at

sending end, MM3-TTK#1)

When a phase-to-ground fault occurs, a heavy short

circuit current or primary arc flows through the faulted

phase until both end breakers trip. The arc transition occurs

at the time the current in fault arc path first reached zero,

after the receiving end breaker trips. Actual current

interruption is arranged to occur at the first current zero

following contact separation of breaker pole. Before final

extinction of secondary arc, several partial extinctions and

restrikes are observed. It is noted that the nonlinear

variation of the arc manifests itself into producing high

frequency components which in turn distort the wave form.

Fig. 9 Primary arc resistance

Fig. 9 depicts the dynamic resistance curve of the

primary arc attained by dividing the arc voltage by the arc

current. It is clearly seen that the fault arc resistance is

highly nonlinear. In particular, it is clear that while the arc

current periodically passes through current zero, the arc

resistance shows small abrupt changes and is primarily

responsible for causing the distortion in the fault arc

voltage.

A series of studies have been performed in similar

manner for each one of the other double circuit between

MM3 and TTK (MM3 TTK#2 and MM3 TTK#3). Fig.

10 and Fig. 11 present the arc current responses from the

simulation for single-line-to-ground fault occurring at the

sending end of the line.

Fig, 10 System response for phase A to ground fault at sending end,

MM3-TTK#2

Fig, 11 System response for phase A to ground fault at sending end,

MM3-TTK#2



10

Following the arc transition at time T3, there is a gradual

build up of the voltage across the arc path until final

extinction occurs at time T4. . The different fault locations

are taken place at the sending end, middle of the line and

receiving end for each simulation. The arc duration, as

considered from studied system, is concluded in Table 1.

Due to highly random and complex behaviour of the

secondary arc it is almost impossible to reproduce the exact

arc duration by digital simulations. However, the simplified

model evaluated in this paper can be employed to

determine maximum dead times in the worst case and to

examine the performance of arc suppression schemes in

reclosing studies. Table 2, 3 and 4 are the studied results

from which it can be summarized that the electrostatic

component of the secondary arc current and recovery

voltage are below 20 A and 50 kV level respectively (often

regarded as the limit for successful reclosing). For the

system studied, the maximum arc duration is 354 ms at

MM3 TTK #1. It is important to reduce dead time setting

and reclose both end breakers as quickly as possible after

completely arc extinction for enhancing the operational

availability of the system.

TABLE 1

SECONDARY ARC EXTINCTION TIME FROM SINGLE PHASE TO GROUND FAULT

Fault location

Secondary Arc Extinction Time after Fault

Inception (ms)

MM3-TTK#1 MM3-TTK#2 MM3-TTK#3

Sending End 354 324 333

Middle Line 343 266 266

Receiving End 333 255 254

TABLE 2

SECONDARY ARC CURRENT AND RECOVERY VOLTAGE FOR PHASE TO GROUND FAULT MM3 TTK#1

Fault location Ifs, A Recovery voltage, kV

Sending End 12.10 43.60

Middle Line 11.20 41.45

Receiving End 9.10 32.84

TABLE 3

SECONDARY ARC CURRENT AND RECOVERY VOLTAGE FOR PHASE TO

GROUND FAULT MM3 TTK#2





TABLE 4

SECONDARY ARC CURRENT AND RECOVERY VOLTAGE FOR PHASE TO

GROUND FAULT MM3 TTK#3





As the main purpose of this study, it is important to

know the worst dead time that must be allow for complete

arc extinction, to prevent the arc restriking when voltage is

re-applied. The successful single-phase reclosing is

evaluated by conducting fault clearing and reclosing cases

utilizing the proposed simplified arc model. The illustrative

cases are presented in order to evaluate approximately the

maximum arc duration that may be expected. To improve

the scheme, the shorten pre-set dead time is investigated

together with compensation of secondary arc; the

successful reclosing will occur and bring the system

stability back. The proposed simplified arc model, which

has been used to assess the performance of the system

operating conditions in this study, can be employed to

determine the maximum dead times in worst case. The

maximum secondary arc duration is 354 ms for the studied

Mae Moh Tha Ta Ko system. The total reclosing time,

including 300 ms for circuit breaker closing time, should be

654 ms. The existing single phase reclosing schemes have

pre-set dead times typically 700 ms ( with total reclosing

time of 1000 ms) that reclose the open breaker phase which

can be shorten by the studied reference.

VI. CONCLUSIONS

Clearance of short-circuit faults on EHV transmission

line is critical for power system stability. Therefore, most

system operators use single phase tripping and reclosing in

order to give single phase arcing faults a chance to

extinguishing while keeping the two healthy phases of the

line in operation. The dead time of the reclosing should be

long enough for the secondary arc to stop burning, and yet

as short as possible in order to reduce the power system

disturbance. Since a same fixed time setting is used for all

EHV lines. In this case, the operators have to decide

whether it is appropriate to manually reclose the line after a

couple of minutes, by assessing the risk of fault restrike.

Due to highly random and complex behavior of the fault

arc, it is almost impossible to reproduce the exact arc

duration by digital simulations. However, the proposed

simplified arc model has been evaluated and can employed

to determine maximum dead times (worst case) and to

evaluate the performance of arc suppression schemes in

single phase reclosing studies.



11

The transient study evaluated the single-phase reclosing

of the 500 kV lines in case of Thailand system between

Mae Moh and Tha Ta Ko substations. The results present

especially emphasised the effect of EHV transmission

system on secondary arc current. The work considers the

characteristic of secondary arc current after clearing of

transitory fault and returning the system to normal

operation. The both primary and secondary arcs behaviour

were implemented in a custom PSCAD/EMTDC model as

a time-varying resistance. This notes that the simplified arc

model is suitable for arcing fault simulation applications.

The successful single-phase reclosing is investigated by

conducting fault clearing and reclosing cases utilizing the

developed arc model. The illustrative cases are presented in

order to determine approximately the maximum arc

duration that may be expected. Due to highly random and

complex behaviour of the secondary arc it is difficult to

reproduce the exact arc duration by digital simulation.

Single phase reclosing schemes detect the presence of

single-phase-to-ground faults on a transmission line and

trigger the circuit breaker of only the faulted phase to open.

To improve the scheme, the shorten pre-set dead time is

investigate together with compensation of secondary arc;

the successful reclosing will occur and bring the system

stability back. However, the proposed simplified arc model

which has been used to evaluate the performance of the

system operating conditions in this study, can be employed

to determine the maximum dead times in worst case. The

results could then be used for further evaluation EHV

system in many different areas such as protection, reclosing

scheme and power quality.

Acknowledgements

The authors would like to gratefully acknowledge the

contributions of Dr. Suthep Chimklai from Electricity

Generating Authority of Thailand and Dr. Dharshana

Muthumuni from Manitoba HVDC Research Centre,

Canada on their technical and information supports, thank

the National Research University (NRU) Project from the

Office of the Higher Education Commission of Thailand.

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12

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