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Insulation Coordination in the Alberta Interconnected Electric System

Part 1

Ligong Gan, P.Eng. Transmission Engineering & Performance Alberta Electric System Operator (AESO)

2

AGENDA

• Why do we need insulation?

• What is insulation coordination?

• Recap of May 13/15 2014 Course by Dr. Peelo – Temporary over-voltages – Switching over-voltages – Lightning over-voltages

• Typical approaches to insulation coordination

• IEEE and IEC standards

• Q&A

Before Lightning Rod was Invented…

3

• Lightning has always been a prominent part of all ancient religions and mythologies in the world

• In the old days, lightning was considered an act of god(s) to express their anger

• For example In the Middle Ages in Europe, it was common practice to ring church

bells during a lightning storm to break up thunderstorms and to avert lightning

The uneducated people believed that this would disperse evil spirits, while the more educated believed that it would cause vibration in air which broke up the continuity of the lightning path

However, during a 33 year period, 386 church steeples were hit by lightning, killing 103 bell ringers at the rope

Characteristics of Lightning

4

• 2000 lightning occurrences on the earth by the time you finish reading this slide

• A lightning flash typically lasts for 0.2s

• Usually made of several shorter discharges, each of which lasts for 10 to 50 µs

• Typical length of lightning path is 2-3 km

• Individual discharges are called “strokes”

• Most visible when return stroke occurs

• Lightning bolt can carry a potential difference of >1000 kV and >100 kA with >20 GJ

Lightning Facts of Alberta

5

• In an average year, 270,000 cloud-to-ground (CG) lightning strikes occur in Alberta (in contrast, Manitoba has only 70,000 per year)

• Most CG lightning occurs in the mountain and west-central areas

• Virtually all CG lightning strikes occur in July (45%), August (32%) and June (23%)

• On a typical day, most lightning strikes happen between 3:00 pm and 11:00 am

• Average lightning strike density in Alberta is only 0.8 to 1 s/km2 • The worst strike density is about 4 s/km2, mainly in two areas, one 20 km north of Edson, and the other 50 km southeast of Edson

• The least density is 0.1 s/km2 in the north and far southeast

Source – Alberta Environment and Sustainable Resource Development (ESRD) website

Power Industry Structure in Alberta

Electric Utilities Act

Market Surveillance Administrator

(MSA)

Balancing Pool

Alberta Utilities Commission (AUC)

Transmission Facility Owners

Distribution Facility Owners Retailers

Independent System

Operator (AESO)

Minister of Energy (Appoints AESO Board Members, MSA & AUC Chair)

Generators

6

Presenter

Presentation Notes

What is AESO?

7

The AESO – • Was formed in 2003 under the Electric

Utilities Act (EUA)

• Contracts with TFOs to acquire transmission services

• Develops and publishes binding ISO rules and standards

• Develops and issues Functional Specifications for projects

• Works closely with TFOs and market participants on transmission projects

Why Do We Need Insulation?

8

1. Public and utility personnel safety

2. Ensure current flows only along conductors

3. Prevent damage to equipment due to high voltage. In particular, prevent or reduce permanent damage to

– Transformers – Cables

How Insulation Breakdown Takes Place

9

• Chemical – Oxidation, hydrolysis, etc.

• Mechanical – Cracks, channels, tracks, deforming, etc.

• Thermal – Overheating (e.g., transformers are generally limited to 2 seconds over-current)

Failure Rate Failure Rate

HV xformers 0.1% Cables ≥ 25 kV 83% of all failures

LV xformers 0.15% CTs 0.35%

HV shunt reactors 0.4% PTs 0.2%

HV breakers 0.09% Surge arresters 0.01%

Typical failure rate of equipment due to insulation breakdown

Source: Research conducted by Bueno & Mak Group.

Insulation Coordination – Definition

10

IEEE 1313.1 – The selection of the insulation strength of equipment in relation to the voltages, which can appear on the system for which the equipment is intended and taking into account the service environment and the characteristics of the available protective devices

IEC 60071-01 – Selection of the dielectric strength of equipment in relation to the operating voltages and over-voltages which can appear on the system for which the equipment is intended, taking into account the service environment and the characteristics of the available preventing and protective devices

Plain Language – Arrangement of insulation levels in such a manner that an insulation failure, if one occurs, would be confined to the place on the system where it would result in the least damage, be the least expensive to repair and cause the least disturbance to the continuity of supply

Insulation Coordination (cont.)

11

Keep in Mind • It’s impossible to design a

system that is 100% protected

• No perfect solution – practicality is the key

• Insulation coordination is both an art and science

• Insulation coordination is often an economic decision

Number of insulator units

Over-Voltage

An Example of Insulation Coordination

12

• Tower type steel

• Shielding wire Yes

• Line BIL = 1050 kV

• Transformer BIL = 850 kV

• Breaker BIL = 1050 kV

• Switch & post insulators BIL = 900 kV

• Arrester – Continuous voltage = 190 kV

– Discharge voltage = 600 kV

• Separation distance ≤ 3 m between arrester & xformer (as per IEEE C62.22)

Tower & Line

Breaker

Transformer

Arrester

240 kV system

Recap of May 13/15 2014 Course “Insulation Coordination” by Dr. Peelo

13

• The following voltages are always phase-to-phase r.m.s. values

– Nominal system voltage – Minimum continuous operating voltage – Maximum continuous operating voltage (MCOV)

• The following voltage is phase-to-ground r.m.s. value – Short-duration low-frequency withstand voltage

• The following voltages are phase-to-ground (sometimes phase-to-phase) peak values

– Lightning impulse insulation withstand voltage – Switching impulse insulation withstand voltage


14

• Nominal system voltage – the phase-to-phase r.m.s. voltage by which the system is designed. It’s generally 10% below the maximum system voltage as defined below

• Maximum continuous operating voltage (MCOV) – the highest phase-to-phase r.m.s. voltage under normal operating conditions – AESO’s reliability standards (TPL and VAR in particular) – AESO’s “Transmission Planning Criteria and Guidelines” specifies

Steady State Voltage Criteria (Table 8.2-1) for transmission elements – MCOV = Extreme Maximum Voltage in AESO’s Functional Spec

What Is MCOV?

15

• Highest voltage under “normal” operating conditions

• Highest voltage for which equipment is designed for satisfactory continuous operation without intended derates

• In defining MCOV, voltage transients and short duration temporary over-voltages are normally excluded

• However, voltage transients and temporary over-voltages may affect equipment operating performance and should be considered in design

Acceptable Range of Voltages in the AIES

16

Nominal (kV)

Extreme Minimum

(kV)

Normal Minimum

(kV)

Normal Maximum

(kV)

Extreme Maximum

(kV)

69/72 62 69 76 79

138 124 135 145 152

144 130 137 151 155

240 216 234 252 264

260 234 247 266 275

500 475 500 525 550 Note: Extreme Maximum kV = MCOV (as mentioned previously)


17

• Over-Voltage – Any voltage that exceeds the MCOV. Often expressed in p.u. with reference to the peak phase-to-ground maximum voltage

1 p.u. = MCOV × 2 ÷ 3

• Critical flashover (CFO) voltage – A voltage with a given waveform that causes flashover on 50% of all tests

The breakdown of most insulation materials is basically probabilistic in nature. It often follows a normal (Gaussian) distribution. The CFO is simply the mean value of the statistical distribution.

Recap of May 15/17 2012 Course “Understanding Grounding” by Dr. Xu

18

• If-1φ can be 3

𝐾+2 times of If-3φ

• TOV can be 3(1+𝐾+𝐾2)

𝐾+2 times of rated V (MCOV)

Where 𝐾 = 𝑍0𝑍1

When 𝐾 < 3 Effectively grounded (as per IEEE and IEC)

At any point of a network,


19

• Representative over-voltage (Urp) – A voltage that produces the same dielectric effect on insulation as over-voltages of a given class occurring in services (There are up to four representative over-voltages in a power system)

• Coordination withstand voltage (Ucw) – for each class of voltage, the value of the withstand voltage of the insulation configuration in actual service conditions, that meets the performance criteria (Adjusted Urp considering inaccuracy of initial data)

• Required withstand voltage (Urw) – the test voltage that the insulation must withstand in a standard withstand test to ensure that the insulation meets the performance criteria when subjected to a given class of over-voltages in actual service conditions and for the whole service duration (Adjusted Ucw considering the difference between standard test conditions and real-life operating conditions)


20

• Coordination factor (Kc) – the factor by which the value of Urp must be multiplied to arrive at the value of Ucw

Ucw = Urp x Kc

• Atmospheric correction factor (Ka) – the factor to be applied to Ucw to account for the actual atmospheric conditions (applies only to external insulation)

• Safety factor (Ks) – the factor to be applied to Ucw to account for the actual service conditions

• Test conversion factor (Ktc) – the factor to be applied to Urw in a given over-voltage class, in the case where the standard withstand shape of the selected withstand test is that of a different over-voltage class


21

• Conventional (deterministic) BIL or BSL – the insulation strength expressed in terms of the crest value of a standard lightning impulse (for BIL) or a standard switching impulse (for BSL) for which the insulation shall not exhibit ANY disruptive discharge (generally applicable to non-self-restorable insulations)

– Applicable to non-self-restoring insulation

• Statistical BIL or BSL – the insulation strength expressed in terms of the crest value of a standard lightning impulse (for BIL) or a standard switching impulse (for BSL) for which the insulation exhibits a 10% probability of failure (generally applicable to self-restorable insulations)

– Applicable to self-restoring insulation


22

Basic Impulse Level (BIL or BSL) The crest voltage of a standard wave (either a 1.2/50 impulse or a 250/2500 impulse) that will not (or in 90% of the tests, will not) cause a flashover of the insulation is referred to as “Basic Impulse Level or BIL”

The insulation strength of equipment as tested should be equal or above the BIL as specified in an AESO’s Functional Spec

1.2/50

250/2500

How the BIL (or BSL) is Determined

23

Ground

Representative over-voltage Urp

MCOV

Coordination withstand voltage Ucw

Required withstand voltage Urw

BIL or BSL Test conversion factor Ktc

Atmospheric factor Ka Safety factor Ks

Coordination factor Kc

(between 5% and 10%) Nominal voltage (138/144/240/500 kV)


24

Standard lightning impulse voltage waveform Standard switching impulse voltage waveform

Temporary over-voltage Very fast front short duration over-voltage

Margins of Protection

25

Mag

nitu

de o

f ove

r-vo

ltage

pu

Fast-front over-voltage (Lightning, µs)

0

2

1

3

4

5

Slow-front over-voltage (Switching, µs to ms)

Temporary over-voltage (seconds to minutes)

Continuous operating voltage (life time)


26


27

Temporary Over Voltage (TOV) • An oscillatory phase-to-ground or phase-to-phase over-voltage, at a

given location and of relatively long duration (1s to 10s), is undamped or only weakly damped

• TOV level establishes the rating of surge arrestors • The general rule is that surge arresters should not activate at TOV but

will activate when experiencing higher voltages

Major causes of TOV • Load rejection • Ground faults • Resonance phenomena or harmonics • Line energization/deenergization

Duration of TOV • Typically 1s to 10s (or minutes in extreme cases)

Surges and Transient Over-Voltages

28

A short-duration highly damped, oscillatory or non-oscillatory over-voltage, having a duration of a few milliseconds or less. Transient over-voltage is normally classified as one of the following types

• Slow front

• Fast front

• Very fast front

Surges and Transient Over-Voltages (contd.)

29

• Slow front (20 µs to 5 ms) – Line energization/deenergization

– Faults or load rejection

– Switching of capacitors/reactors

• Fast front (0.1 µs to 20 µs) – Lightning

– Switching operations

• Very fast front (1 ns to 0.1 µs) – Switching of disconnects or circuit

breakers (typically with GIS applications)

Class and Shapes of Over-Voltage and Tests

30 Source: IEC 60071-2

Over-Voltages Amplitudes

31

Power-Frequency Temporary Over-Voltage • Generally ≤ 10s

SLG faults <1.5 pu Ferranti effect <1.3 pu Load rejection < 1.4 pu Resonance > 2 pu Energization/re-energ. < 1.5 pu Stuck breaker pole < 2 pu

Lightning Over-Voltage • Fast front 1-6 µs > 5 pu

Tail @ 50%: 50 µs

Switching Over-Voltage • Slow front 30-300 µs

Tail @ 50%: 100-2000µs Energizing lines 1.5-2 pu Re-energizing lines 3-3.4 pu Switching no-load xformr > 2 pu Switching reactor > 2 pu Switching capacitors 1.5-2 pu Fault interruption 1.5 pu

Typical Insulation Coordination Studies

32

Transmission substation insulation coordination study • Primary purpose is to determine the location of lightning masts, location and rating

of surge arresters, the mitigation techniques such as pre-insertion breakers, point-on-wave breaker control, current-limiting reactors, and to determine appropriate protection relay settings

• Look at all sources of surge over-voltages: Temporary over-voltage, switching surge and lightning surge

• Determine the probabilities and protection margins for all transients entering the substation

Transmission line insulation coordination study • Primary intention is to determine

– Location of arresters if back flashover is of a concern – Necessity and location of arresters if the terminal breakers do not have pre-insertion

resistors

Power plant (including WAGF) or user-owned substation IC study • Typically performed by the owner of the power plant or substations • Similar to transmission substation insulation coordination study for the substations • Primary intention is to determine grounding requirement and location of surge

arresters

Over-Voltage Protection Devices

33

Surge arrester

Pre-Insertion Resistor

Controlled closing

Grounding

More insulation

Shielding wire

Characteristics of SiC and ZnO Arresters

34

Characteristics of different surge arresters

Selection of Surge Arresters

35

• Location • Maximum continuous operating voltage • Amplitude and shape of over-voltages

• Nominal discharge current

• Residual voltage at the nominal discharge current

• Energy absorbing capability (Arrester class) • Surge impedance and/or capacitance of the

protected equipment

Selection of Surge Arresters

36

Example – Find a suitable lightning arrester for a 240 kV transformer. For the transformer, MCOV = 264 kV (=240×110%) and BIL = 850 kV (as per AESO FS) Therefore, the arrester’s voltage rating (Vr) and continuous operating voltage (Vc) is ≥153 kV (= 264 ÷ 3) The following arresters can be chosen:

Voltage Rating (kV rms) TOV (kV rms) (10 sec)

Max Residual Voltage (kV peak)

Vr Vc SPL (1 kA) 30/60 µs

SPL (2 kA) 30/60 µs

LPL (5 kA) 8/20 µs

LPL (10 kA) 8/20 µs

210 156 231 417 433 469 494

240 191 264 476 495 536 564

276 221 303 547 569 617 648

Insulation strength (BIL) = 850 kV Therefore, protective margin = (850/564 – 1) = 0.51 or 51% (which is >25%) Assuming an effectively grounded system, and the power frequency over-voltage is limited to no more than 40% at the arrester, so MCOV × 140% = 153 × 140% = 214 kV (which is less than 264 kV)

Procedure for Insulation Coordination

37

Determination of representative over-voltage Urp

Determination of coordination withstand voltage Ucw

Determination of required withstand voltage Urw

Rated or standard insulation level Uw

• Transient analysis & simulation • Origin and level of over-voltages • Statistical distribution of over-voltages • Protective level of arresters • Insulation characteristics • Determine contamination severity • Verification of data and assumptions • Determine coordination factor Kc

• Determine altitude correction factor Ka • Determine safety factor Ks

• Determine test conversion factor Ktc • Determine level and range of Uw (for

both internal and external)

Kc

Ka Ks

Ktc

Differences between IEEE and IEC

38

• Both IEEE 1313 and IEC 60071 are excellent reference standards • Procedures and methodologies in both standards are same or similar • In many cases IEEE 1313 cites directly IEC 60071 recommendations • The differences are minor and subtle

IEEE 1313 IEC 60071

Nomenclature BIL, SIL LIWV, SIWL, ACWV

Detail Tend to be concise Detailed with more examples

Performance criteria Generally more “aggressive”

Generally more “conservative”

MCOV ≥ 15 kV ≥ 1 kV

Typical Nominal, Minimum, MCOV and BIL Values in AESO’s Functional Specification

39

Nominal (kV)

Minimum (kV)

MCOV (kV)

BIL (kV)

25 23 28 150

69 62 79 350

138 124 152 650

144 130 155 650

240 216 264 1050

500 475 550 1800

Insulation Coordination for Transmission Lines

40

Transmission Line Insulation Coordination Involves

• Shielding angle of the shielding wire • Clearance of conductors • Selection of the type and length of insulators

Keep in Mind

• Shielding Failure Flashover Rate (SFFOR) and Back Flashover Rate (BFR) are two typical design criteria – typical SFFOR is 0.05 f/100km-yr and BFR is 1 f/100km-yr

• The higher the tower and voltage, the smaller the shielding angle • BFR impacts substation insulation requirements • Contamination influences creepage distance (mm/kV) and consequently

the number of insulator units • Generally, from an insulation perspective, transmission line reliability

performance is 10% of substation reliability criterion

Insulation Coordination for Substations

41

Substation Insulation Coordination Involves

• Determination of BILs for major equipment or equipment group • Location of shielding masts and/or shielding wires • Clearance of conductors • Surge arresters – Rating, number & locations

Keep in Mind

• MTBF (and BFR) determine if line-entrance arresters are required • Transformers and cables should always be primary concerns • Protective margin is generally for non-self-restoring insulation • Cost of equipment failure generally determines sequence of failure • Gap configuration can change CFO level by ±30% • Lightning flash can be multiple strokes – longitudinal insulation • There may be back-and-forth calculations/adjustments required

Protection and Insulation Coordination of Substation Components

42

Substation Type

• Air-insulated substation • Gas-insulated substation

Major Equipment

• Transformers

• Circuit breakers

• CTs and PTs

• Capacitors/Reactors

• Cables

http://www.google.ca/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http://www.abb.us/cawp/seitp202/7d8ecd660a395730c12579820035d9e6.aspx&ei=fRHZVPOmHdTToAS63IGoBA&bvm=bv.85464276,d.cGU&psig=AFQjCNE76MeOMv3HhCMUddLwAcDkRtfLCg&ust=1423598216464644

Insulation Coordination between T and D

43

General Principles

• Similar to protection coordination between transmission and distribution

• Should a surge result in insulation breakdown, it should generally be on the distribution system first

• Interruptions to consumers are more confined and

localized, i.e., fewer customers impacted per event

• Distribution utilities are generally closer to the failed equipment – faster response

Typical BIL Levels of Distribution Class & Power Class

44

Voltage (rms kV)

Distribution Class BIL (kV)

Power Class BIL (kV)

5 60 75

8.7 75 95

15 95 110

25 110 150

34.5 150 200

72 250 350

Insulation Coordination between T and G

45

Keep in Mind • Rotating machines (incl. generators/motors) do not have BIL

ratings • For conventional power plants, insulation coordination is primarily

between plant substation and TFO system Wind Aggregated Generating Facility (WAGF): • Most wind power plants in Alberta use 34.5 kV collector systems • Most wind generators (WTGs) are not typically grounded • Induction WTGs can continue to generate if sufficient capacitance

is present (self excitation) – voltage can be high • As above, MCOV and TOV can become constraints for arresters • Most WTGs use distribution class equipment (for economic

reasons) with up to 150 kV BIL

Insulation Coordination between Transmission Lines and Substations

46

General Principles

• Insulation performance of overhead lines has a large impact on the insulation performance of substations

– Re-energization operations

– Towers close to substations

• Transmission lines should be designed to enable no injection of over-voltage in excess of the rated impulse withstand voltage of the connecting substations into the substations

• In mountain areas, the reduction in Critical Flashover (CFO) voltage due to higher elevations should be taken into account

• Substation insulation strength should be at least equal to line insulation strength for switching surges if no line-side arresters

Things to Remember in Insulation Coordination

47

• The TFOs and Market Participants, not the equipment manufacturers, are responsible for insulation coordination studies

• There is nothing more important than “knowing your system better”

• There is not always a “single best solution” to insulation coordination

• Back-and-forth calculations and adjustments are often needed in insulation coordination studies

• Deterministic approach should always be applied to non-self-restoring equipment

• Statistical approach can be applied to self-restoring equipment

• Surge arresters are generally not used to limit temporary over-voltages (TOVs)

Things to Remember in Insulation Coordination (cont’d)

48

• Basically, the basic impulse level (BIL) is equal to the Representative Over-Voltage Urp with many correction factors on top

• Insulation coordination is both an art and science, and is often an economic decision. Many parameters or requirements are conflicting in reality. Example – To reduce BFR of a transmission line Option: increase conductor spacing and insulator units larger tower higher cost and increased surge impedance increased BFR

• Power system insulation is an ever-evolving field. More research needs to be done to more fully understand the transient behavior of lightning, switching surges, etc. IEEE 1243 – Guide for Improving the Lightning Performance of Transmission Lines says – The methods for estimating the lightning performance of transmission lines show

several approaches to a real‐life engineering problem that is ill‐defined. Precise constants are rarely known and are often not really constant, input data is difficult to describe mathematically except in idealized ways

THANK YOU

Questions?

Insulation Coordination in the Alberta Interconnected Electric System

Part 2

Ligong Gan, P.Eng. Transmission Engineering & Performance Alberta Electric System Operator (AESO)

2

APIC Insulation Coordination – Agenda

• AESO’s role in transmission system insulation coordination

• Evolution of BIL requirements in Alberta

• Insulation Requirements in AESO’s Functional Specifications

• Thoughts on Possible Future Changes to Current BIL Levels

• Q&A

The Power Industry of Alberta

3

Distribution

Retail

Transmission

Generation Competition

Regulated

AESO

Power Industry Structure in Alberta

Electric Utilities Act

Market Surveillance Administrator

(MSA)

Balancing Pool

Alberta Utilities Commission (AUC)

Transmission Facility Owners

Distribution Facility Owners Retailers

Independent System

Operator (AESO)

Minister of Energy (Appoints AESO Board Members, MSA & AUC Chair)

Generators

4

Presenter

Presentation Notes

AESO’s Core Functions

5

System Operations Direct the reliable 24/7 operation of

Alberta’s power grid

Transmission System Development

Plan the transmission grid to ensure continued reliability to

facilitate a competitive market and investments in new supply

Transmission System Access Provide access for both electricity

generators, large industrial customers and distribution utilities

Market Services Develop and operate Alberta’s

real-time wholesale energy market to facilitate fair,

efficient and open competition

Alberta’s Bulk Transmission System 240-500 kV (now and near future)

Virtually all 240 kV lines

The KEG loop (500 kV)

Two 500 kV HVDC lines between Edmonton area and Calgary area

Two 500 kV AC lines planned from Edmonton area to Fort McMurray area

One 500 kV AC interconnection to British Columbia

One 240 kV interconnection to Montana

One 150 MW (HVDC) interconnection to Saskatchewan

6

Dover

Ellerslie Genesee Keep - hills

Sundance

Wabamun Clover Bar

Sheerness

Sarcee Langdon

Deerland

Battle River

Brazeau

McMillan

Milo West Brooks

Metiskow

Red Deer

Sagitawah

Louise Creek

Mitsue

Little Smoky

Wesley Creek

Bickerdike

Benalto

Beddington

Peigan

N . Lethbridge

Marguerite Lake

Cordel

Anderson

Josephburg

Jenner

Empress E . Calgary

Goose Lake

L eismer Christina

Lake

Conklin

Janet

Bowmanton

Whitla

‘ MATL ’

Etzikom Coulee

Chapel Rock

Filder Windy Flats

Stavely SC 1

SS - 65

Foothills

Shepard

Crossing

Bennett

Cassils

Sunnybrook

H e art Lake

Heathfield

Heartland

Hansman Lake

Pemukan

Lanfine

Thickwood

Livock

Newell

SC 2

Whitefish Lake

Brintnel l

Presenter

Presentation Notes

Alberta’s Existing Transmission System

Voltage Substations (energized)

Xmission Lines (km) (energized)

TFO Customer TFO Customer

69/72 kV 70 11 2,246 21

138/144 kV 403 57 12,824 282

240 kV 101 23 10,361 223

500 kV 8 602

Note: Circuit length (km) includes both overhead lines and underground cables

Presenter

Presentation Notes

Evolution of Insulation Requirements in Alberta Transmission System

8

First 138 kV line – 80L from Ghost Substation to Edmonton was built in 1929

MCOV of the first 138 kV line 80L was set at 145 kV (105%)

Today – the following MCOV and BIL levels are used:

138 kV 144 kV

MCOV 152 155

BIL (1) 550 550

BIL (2) 650 650


9

First 230 kV line, between Wabamun and Sarcee 42S was built in 1961

MCOV of the first 230 kV line was set at 242 kV

Wabamun had to operate at 253 kV in order to maintain acceptable voltage at Sarcee

Because of the circuit length (>450 km), special equipment with MCOV of 264 kV was installed at Wabamun

The system was then classified as “240 kV nominal voltage”

BIL levels of 900 kV and 1050 kV were chosen, assuming a grounding factor of 1.4


10

In 1986, first 500 kV tie-line 1201L, between Langdon and Cranbrook (B.C.), was built

In 1982, first intra-Alberta 500 kV line 1202L, between Keephills and Ellerslie, was built but operated at 240 kV

In 2010, 1202L re-energized at 500 kV

MCOV of 1201L/1202L was set at 550 kV

BIL of 1425/1550/1800 kV chosen for substations 89S/320P/102S

Since around 2011, 1550/1800 kV became BIL levels for 500 kV system

Dover

Ellerslie Genesee Keep - hills

Sundance

Wabamun Clover Bar

Bowmanton

Whitla

‘ MATL ’

Etzikom Coulee

Chapel Rock

Filder Windy Flats

Stavely SC 1

SS - 65

Foothills

Shepard

Crossing

Bennett

Cassils

Sunnybrook

H e art Lake

Heathfield Heartland

Hansman Lake

Pemukan

Lanfine

Thickwood

Livock

Newell

SC 2

Whitefish Lake

Brintnel l

Existing 240 kV Existing 500 kV

Thermal Plant Hydro Plant

AIES Transmission System

500 / 240 kV System Overview

Future 240 kV Future 500 kV Future 500 kV HVDC

AESO’s Role in Transmission Insulation Coordination

11

In general, AESO only defines functionality requirements of transmission elements in its Functional Spec Operating conditions of equipment Input and desired output (for RASs etc.) Provides a direction (or guidance) for design Reference for equipment bidding and procurement Requirements (or guidance) for compliance with standards

A Functional Specification does not Define inner workings Specify the manufacturer to be used or avoided Dictate how equipment is procured Provide details of how equipment is installed

AESO’s Role in Transmission Insulation Coordination (cont’d)

12

Typically, AESO’s Functional Spec contains

Purpose Interpretation and Variances Project Overview Scope of work

Standards Scope of work for TFO and Market Participant

Transmission System Operating Characteristics Normal operating levels and constraints Emergency operating requirement

Appendices Single line diagrams for substation configuration and SCADA

requirements

Some Relevant Rules & Standards

13

• ISO rule 502.1 – Wind Aggregated Generating Facilities Technical Requirements Section 21 provides lightning surge protection requirements for the collector stations, and between collector substation and transmission line

• ISO rule 502.2 – Bulk Transmission Line Technical Requirements Specifies the standards to be used in setting electrical clearances, the conditions under which an insulation study is required, and the minimum insulation levels of a bulk transmission line The Information Document (ID) further provides detailed explanation as to how insulation coordination is conducted, and the recommended BIL levels

• Generation & Load Interconnection Standard 2006 Section 2.3 sets out the general requirements for insulation studies and the specific IEEE standard (P998) to be employed

• ARS FAC-001-AB – Facility Connection Requirements Section R2.6 requires that the AESO’s interconnection requirement or project’s Functional Spec must address insulation and insulation coordination

AESO’s Philosophy on Insulation Coordination

14

• AESO specifies rules & standards which set out minimum technical requirements

• AESO provides minimum BIL levels without distinguishing

– between BIL & BSL – between conventional & statistical

• TFOs and market participants are required to perform any and all insulation coordination studies and determine appropriate insulation levels

• TFOs and market participants are required to coordinate with each other in setting equipment insulation levels

AESO Rule 502.2 – Transmission Lines

15

• Section 14(2) – Shield wires must be installed on 138/240/500 kV AC or ±500 kV DC bulk transmission lines

• Section 14(3) – Number and positioning of the shield wires must be so as to produce lightning flashover rates that are consistent with all reliability requirements of the lines

• Section 17(5) – Electrical clearances for use with the wind pressure values of Table 3 must be determined from the application of the methodology outlined in IEEE Standard 1313.2 “The Application of Insulation Coordination”, for transmission line phase to ground switching over voltages


16

• Section 21(7) – The minimum insulation levels for a bulk transmission line and any 25 kV distribution line located on bulk transmission line structures must be as set out in the following table:

• ID 2010-005R, Section 21 – Insulation levels for 500 kV AC or ±500 kV DC lines are determined from insulation studies carried out for each such line, as part of the design process.

Nominal Voltage (kV) Critical Impulse Flashover CIFO (kV)

25 kV 165

138/144 kV 715

240 kV 1,155


17

• ID 2010-005R, Section 21 – 25 kV insulation requirement applies only to those 25 kV distribution lines placed on bulk transmission line structures. 502.2 recognizes the need for insulation coordination between circuits of different voltages located on common structures

• ID 2010-005R, Section 21 – Insulation levels for 500 kV AC or ±500 kV HVDC lines are determined from insulation studies carried out for each such line, as part of the design process. Hence, 502.2 does not include insulation levels for 500 kV class lines

AESO Functional Specification

18

In the “Project Scope” section:

• (the legal owner of the transmission facility) shall complete insulation coordination studies and coordinate with the market participant as required to establish appropriate insulation levels

• Undertake insulation, grounding, protection and communication studies as necessary to accommodate the proposed system additions and modifications

AESO Functional Specification

19

6.3 Insulation Levels (1) The following provides the minimum required basic impulse levels for the transmission system. Station equipment with lower insulation levels may be used provided that protection and coordination can be maintained with judicious insulation design and use of appropriate surge arresting equipment.

(2) For 25 kV circuit breakers where there is a grounded wye transformer and surge arrestors are installed, a basic impulse level of 125 kV is acceptable.

Nominal Voltage (kV rms) 25 69/72 138/144 240 500

Station post insulators and airbreaks 150 350 550 900 1,550

Circuit breakers 150 350 650 1,050 1,800

Current and potential transformers 150 350 650 1,050 1,800

Transformer windings (with arresters) 150 350 550 850 1,550

Thoughts on Possible Future Changes to Current BIL Levels

20

• Should we split the current basic insulation levels into BIL and BSL levels?

• In some 500 kV projects, it has been suggested that the BIL level for the 500/240 kV autotransformers be set at 1425 kV for lower cost and easier transportation

• Should we create a new nominal voltage level of 260 kV with MCOV of 286 kV (or 275 kV)?

• Should we raise the current BIL for 240/260 kV transformers from 850 kV to 900 kV (or higher)?

• Should we differentiate GIS from AIS equipment, especially for 500 kV equipment, on the BIL levels?

• Any other from you?

Upcoming AESO Rule for Substations – 502.11

21

• The AESO is now in the process of developing a Substation Rule (502.11) which sets out the minimum technical requirements respecting design, engineering and construction of (new) transmission substations

• Insulation coordination and grounding will be a major part of Rule 502.11

• Proposed Process (2015-2016) – Industry Workgroup (WG)

– Recommendation paper to WG & stakeholders

– Draft and post Rule for comments from industry

– Filing of Rule 502.11 with AUC

http://www.google.ca/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http://kiran111.hubpages.com/hub/Power-Substation-Types&ei=hRTZVJTsDMOvogS28oH4AQ&psig=AFQjCNEmk9XopaYrfSplZWi4d0_iCbLhGA&ust=1423599090501336

THANK YOU

Questions?

University of Alberta

Over-Voltages and the

Distribution System

Thomas C. Hartman, P.Eng.

APIC – Professional Development

May 12 & 14, 2015

University of Alberta 1

Discussion Outline - OVERVIEW

• The Origin and Shapes of Distribution System Surges

• Insulation Systems – And How They Go Bad

• Where Surges Matter – And What They Do – Overhead Systems

– Underground Systems

• Distribution Surge Arresters – Design and Application

• Reality Check

• Q & A

NOTE: References are in parenthesis - (xx)


Disclaimer

I will mention many companies during this presentation.

Please keep in mind:

1 – I have NO financial interest or otherwise in any of the

companies I mention

2 – I work for ATCO Electric Distribution and that is my only

source of income

3 – This presentation is my opinion only and does not

necessarily reflect ATCO policy, practices, or standards

4 – I expect that you will use this presentation for illustrative

purposes only. Any arrester applications you design shall

be based on your own professional judgement


The Origin and Shapes of

Distribution System Surges

• Overhead

• Underground – Mostly same as O/H,

but with some twists!

(16)

(1) (2)

(12)


What is a Surge?

Surge

• IEEE Std 100: “A transient wave of current, potential, or power in an electric circuit. Note: The use of this term to describe a momentary overvoltage consisting in a mere increase of the mains voltage for several cycles is deprecated. See also: swell.”

Temporary Overvoltage (TOV)

• IEEE Std 100: “. An oscillatory overvoltage, associated with switching or faults … and/or nonlinearities … of relatively long duration, which is undamped or slightly damped.”


TOV

It is NOT a Surge!

• Accidental Grounding - Leg of Delta

• Loss of Neutral

• Fault Conditions

• Comingling

“When Overbuild Meets Underbuild”

Surge arresters provide a simple solution to a complex overvoltage

problem

Daniel J. Ward, Dominion Virginia Power

T&D World Magazine - Mar 1, 2011


World Ground Flash Density

www.arresterworks.com/resources/calculator_images/GFD_World.jpg


A Natural Cause - Lightning

(13)

Lightning Current MIL-STD-464

(14)

(3) (15)


Vacuum Switch TRV Behavior (7)

Simulated TRV Response Source Voltage: 3.4 kV (6 kV System)

Current at Opening: 4.7 A


Shunt Capacitors

(5)

Effect of switching re-strikes on capacitor voltage

(6)


Current Limiting Fuse Operation

(11)


Current Limiting Fuse Arc Interruption Voltage

(34)


Other Surge Waveforms

Switching Surge (36)

(37)

(38)


Surges and Their Waveforms

Just So YOU Know…

Lead Length can ADD up to 1500 Volts/Foot

Lead length is the physical wire distance between the

Apparatus and the Line Side of the Surge Arrester

PLUS (+)

The Line Length from the Ground of the Surge

Arrester to the Ground of Apparatus

AND for the Love of Goodness,

Please Don’t COIL the Leads!!!


Insulation Systems

And How They Go Bad

If we lived in a perfect world, our insulation systems

would last forever. But…

We don’t.

All Insulation Systems are Doomed from the Start!

• Embedded Manufacturing Defects

• Environmental Contamination

• Shipping and Handling

• “Some” Field Assembly Required (32)


Insulation Systems– How Do They Fail?

External Sources

• Physical Damage – “Rocks and Rifles”, External Arc

• Contamination – Farming, Exhaust, Salt, etc.

Internal Sources

• Water Ingress

• Arcing under Oil or SF6

• “Built-In” Defects – Either from Vendor or Customer


Insulation Systems

Contamination and Built-In Defects

Contamination – Surge Arresters Really Won’t Help

• The Failure Mechanisms Associated with

Contamination are Active at 60 Hz System Voltage

“Built-In” Defects – Surge Arresters May Help

• If the Failure Mechanism is Triggered by a Surge,

then a Surge Arrester will Delay the Trouble

• If the “Built-In’ Defect is Active at System Voltage,

then a Surge Arrester Won’t Help.


Insulation Systems – Failure Triggers

Contamination

• Dry Band Arcing is the Beginning of the End

“Built-In” Defects

• It is All About Capacitance, Dielectric

Constants, and Dielectric Strength

• C = (k*e0*A)/d

where k: Air =1, Silicone = 4, EPDM = 2.6

Glass = 6, Polyethylene = 2.25, Porcelain = 6

Which Equals an Evil Voltage Divider


Ceramic / Glass

• One Tough Insulation System!

• Can Last a Century or More

• Surges / Flashovers are Generally Benign

Failure Mechanisms

• Slow Clearing Times Crack Ceramic/Glass

• Susceptible to Point Pressures Resulting in Crack

Propagation

• Pin Threads (lead/nylon)

• Ice Expansion Forms Cracks

• External Contamination / Cleaning


Polymers

Organic/Semi-Organic System

• Manufacturing Process

Sensitive

Failure Mechanisms

• Embedded

Manufacturing/Material Defect

• If Small Enough, the Defect

Lays Dormant Longer

• Surges Reduce PD Inception

Levels

• Ultimate Demise of Insulator (30)

(31)


Dielectric Fluid – Oil (29)

1. Oxidation: Oxidation is the most common cause of oil deterioration, which is the reason

that transformer manufacturers are careful to seal the transformer from the atmosphere.

2. Contamination: Moisture is the main contaminant. Its presence can react with the oil in the

presence of heat. It also lowers the dielectric properties of the insulating oil.

3. Excessively high temperature: Excessively high heat will cause decomposition of the oil

and will increase the rate of oxidation. The best way to avoid excessive heat is to avoid

overloading the transformer.

4. Corona discharges: Arcing and localized overheating can also break down the oil,

producing gases and water, which can lead to the formation of acids and sludge.

5. Static electricity: The existence of an insulating fluid flowing past an insulating solid

(paper), results in charge separation at the interface of the two materials. Physically, these

charges separate at the interface of the oil and paper in any transformer; thus reducing the

dielectric strength of the insulating oil. This could also cause internal flashover.

6. Furans: Furan derivatives are a measure of degradation of paper insulation. When the

paper ages, the long-chain cellulose molecules (polymers) break down in smaller fractions

and its physical strength is reduced. The degree of polymerization can be directly related to

the concentration of furan derivatives, which are formed in the oil.


SF6 (28)

Sulfur hexafluoride (SF6) is a relatively nontoxic gas used in a number of applications for its

inert qualities. The dielectric and other physical and chemical properties related to its lack

of reactivity have led to the extensive use of SF6 as an insulating medium in switching

equipment (e.g., circuit breakers) by electric utilities. While SF6 is inert during normal use,

when electrical discharges occur within SF6-filled equipment, toxic byproducts can be

produced that pose a threat to health of workers who come into contact with them.

SF6 can decompose into byproducts when exposed to four types of electric discharges

(CIGRE1 1997)

• partial corona discharges caused by insulation defects;

• spark discharges that occur at insulation defects or during switching operations;

• switching arcs that occur in load break switches and power circuit breakers; and

• failure arcs that occur due to insulation breakdown or switchgear interruption failure.

Each discharge can result in different mixtures and concentrations of byproducts.


Where Surges Matter ~ OVERHEAD SYSTEMS

And What They Do There

Pin Insulator

Transformer

Regulator

Capacitor

Riser Pole

On the Secondary


At the Pin Insulator (16)


At the Transformer

(9) (24)


At the Secondary

Transformer Secondary Protection

Surge Suppression Inc.

EATON’s Cooper Power Systems At the secondary bushing – Inside (9)


At the Capacitor (17)

(18)

(17)


At the Regulator

(19)

(35)


Where Surges Matter ~ UNDERGROUND

And What They Do There

Underground Systems

• Riser Pole

• Cable

• At an “Open Point”


At the Riser Pole

(20)

(21)

(22)


In the Cable

(25)

(26) (26) (27)


At an “Open Point”

(4)

(10)


At ANY Place on your System

Just So YOU Know…




PLUS (+)






Distribution Surge Arresters

Design and Application

• A Very Brief History of Surge Arrester Evolution

• Explanation of Surge Arrester “Classes”

• Which Class to Use

• How Arresters Eventually Fail

• Surge Arresters have ONE Job – Protect Insulation


A Brief History

• Air Gap – Beginning of Time to Now

• Silicon Carbide (SiC) – 1930 to Mid 1980s

• Metal Oxide Varistors (MOV) – 1975+

http://www.arresterworks.com/ http://www.arresterworks.com/

(41)


Differences Between Manufacturers

• None Really

• Arresters are essentially COMMODITIES

• Purchase on your preferences such as:

• Price

• Vendor Service

• Availabilities

• Vendor Preference

• Etc.

• You will likely be satisfied!

• My Preference???


Surge Arresters – Parameters

Critical Parameters (Minimum Needed)

1. MCOV – Maximum Continuous Operating Voltage

2. TOV – Temporary Over-Voltage Withstand

3. EFOW – Equivalent Front-of-Wave (0.5 uS, Lightning)

Lesser Parameters (May be hard to Coordinate)

4. Discharge Voltage – At: 1.5 kA, 5 kA, 10kA, & 20 kA

5. Switching Surge – 250 or 500 amps (Class Dependent)

6. Arrester Class – ND, HD, RP, Intermediate, Station

Only 6?!, Really?!

But What is a Surge Arrester RATING?!


Critical Parameter #1 – MCOV

Nominal System

L-L Voltage

Maximum

L-L Voltage

Maximum

Line to GND

Voltage

Solid Multi-

Grounded

Systems

(4-Wire)

Uni-Grounded

Systems

(3-Wire)

Impedance

Grounded,

Ungrounded,

and Delta

Systems

kV rms kV rms kV rms MCOV MCOV MCOV

4.16 4.37 2.25 2.55 5.1 5.1

4.8 5.04 2.91 -- -- 5.1

6.9 7.25 4.19 -- -- 7.65

24.9 26.2 15.1 15.3 22 --

Do You See a RATING Here?


Critical Parameter #2 – TOV (41)


Critical Parameter #3 – EFOW (BIL)

(39)


Lesser Parameters 4 & 5

4. Discharge Voltage – At: 1.5 kA, 5 kA, 10kA, & 20 kA

5. Switching Surge – 250 or 500 amps (Class Dependent)

These two parameters will one used based on the type

of equipment you are protecting.

The Discharge Voltage is use at the “End” of Lightning

Protective Levels.


Capacitors – Coordinate to Surge Arrester

According to network rated voltage, the insulation level of equipment is as follows :

Rated Voltage (Vdim) Insulation Level Power Frequency Voltage

Withstand

(kV rms)

Impulse Voltage Withstand

(kV peak)

(V) (kV)

6600 7,2 20 60

11000 12 28 75

15000 17,5 38 95

22000 24 50 125

33000 36 70 170

(40)

Schneider Electric – Hong Kong General Specification for Fixed Capacitor Bank for Electrical Network up to 36kV


Insulators – Coordinate to Surge Arrester

PPC Pin Type Insulators

Catalog Number Frequency 253-S 261-S 263-S 366-S 380-S 386-ST

ANSI Class 55-2 55-3 n/a 55-4 55-5 55-6

Neck Type C C C F F J

Typical Application (kV) 60 Hz 7.2 11.5 11.5 13.2 14.4 23

Dry Flashover Voltage (kV) 60 Hz 45 55 55 65 80 100

Wet Flashover Voltage (kV) 60 Hz 25 30 30 35 45 50

Puncture Voltage (kV) 60 Hz 70 90 90 95 115 135

Impulse Flashover Positive (kV) Impulse 70 90 90 105 130 150

Impulse Flashover Negative (kV) Impulse 85 110 110 130 150 170

Leakage Distance 5" 7" 7" 9" 12" 15"

Dry Arcing Distance 3 3/8" 4 1/2" 4 1/2" 5" 6 1/4" 8"

Cantilever Strength (lbs) 2500 2500 2500 3000 3000 3000

Minimum Pin Height 4" 5" 5" 5" 6" 7 1/2"

Net Weight per 100 (lbs) 183 225 260 390 500 890

Package Weight per 100 (lbs) 191 254 288 400 617 938

Standard Package Quantity 48 24 24 12 12 8


Arrester Class - Parameter #6

• Normal Duty (ND)

• Heavy Duty (HD)

• Riser Pole (RP) (Not a Real Class)

• Intermediate Class

• Station Class

Arrester Class size is Mostly Determined by the

Diameter of the MOV Disk

ND = 1”, HD = 2”, RP = 2”, Inter. = 3”, Station = 4”+


Class Comparisons

Rated

0.5 μsec

10kA500 A

Hubbell

Product

Voltage

kV

MCOV

kVEFOW

Switching

Surge1.5 kA 3 kA 5 kA 10 kA 20 kA 40 kA

1 sec

kV rms

10 sec

kV rms

Normal Duty PDV65-Optima 18 15.3 62.8 46.4 50.1 53.8 57 63.3 72.6 91.2 22.7 21.7

Heavy Duty PDV100-Optima 18 15.3 60.6 43.5 45.4 48.4 51.3 56.4 63.5 75.5 23.5 22.2

Riser Pole PVR-Optima 18 15.3 53.4 35.5 38.9 41.9 44.3 48.9 56.1 66.2 22.2 21.0

Intermediate PVI-LP 18 15.3 51.6 38.3 40.9 43.2 45.2 48.8 54 60.9 21.4 20.5

Station EVP 18 15.3 51.6 36.1 38.5 40.4 42.4 45.5 49.1 56.1 21.7 20.8

8/20 Test Waveform

Maximum Discharge Voltage - kV

Tempoary

Over-Voltage


Protection Level

(33)

Protective Margin = ((Insulation Level / Arrester Discharge Voltage) – 1) * 100%


Generic MOV I-V Curve


(42)


Which Arrester Class – What Purpose?

• Your Choice… In Alberta, a low lightning region -

Normal Duty is good enough for general purpose

protection

• Riser Poles – How important is the circuit?

• Capacitors

– Normal Duty is OK,

– Big Banks consider Heavy Duty or Intermediate

• Transformers

– Normal Duty is OK

– Big Expensive Transformers… Heavy Duty or Intermediate


Surge Arresters – How Do They Fail?

• TOV is the Number 1 Killer of Surge Arresters in

Alberta (As reported on Global National, just kidding…)

– The Process is Simple: Overvoltage Physically Heats the

MOV disk, Heat Lowers the MCOV Which Increases the

Heat Generated, Which Lowers the MCOV More, Which

Increases th Heat Generated, until BOOM!

• Today’s Surge Arresters Rarely Fail Due to a Surge

in Alberta. The Quality is Really That Good!


Surge Arresters – Disconnector

(41)


~ Reality Check ~

Should You Be Worried about a Surge Armageddon?

(23)


~ Reality Check ~

No, of course not.

Your own historical data is proof!

But, Asset Life would be Extended Significantly with

the Proper Application of Surge Arresters!


Where to Focus Your Protection

• Transformer Primaries – SHORTEST Lead Length!!!

• Riser Poles – SHORTEST Lead Length!!!

• UG Open Points

• Regulators – Primary & By-Pass

• Reclosers – Line AND Load Sides

• Capacitors

• O/H Dead Ends and N/O Switches


Careful There, Electrical Current!

One Last Thing…

Be Careful Where You Place an Arrester

• Fuses – Surge Current Will Hurt a Fuse

• Capacitors, Regulators, Reclosers, etc

There is NO line or load on these devices,

at least as surge currents are concerned.


Where to Focus your Protection

Just So YOU Know…




PLUS (+)






A Shameless Promotion arresterworks.com

Deborah Limburg Web and Business Developer

Deborah is a long term veteran in the arrester industry having worked for

Cooper Industries for over 25 years. During that time she held a number of

positions in the product engineering department, including leader of the

Engineering Design Services group. One of her major accomplishments at

Cooper was the design and implementation of a virtual product drawing

systems for all major product lines. This lead to a considerable reduction in

the number of Designers and CAD operators required to maintain the

product documentation system. This database system also helped to

improve the overall documentation process due to the reduction in human

errors.

Additionally she developed the software to handle disk selection process for

the tightly matched disk columns required for series capacitor banks and

the management of the varistor assembly process. Deborah received her

BS in Computer Software from the University of New York State and is a

co-inventor on several US patents.

Since 2010 Deborah has been the Web and Business Developer for

Arresterworks.

Contact at 716-378-1419 or [email protected]

Jonathan Woodworth Principal Engineer

Jonathan started his career at Fermi National Accelerator Laboratory in

Batavia, Illinois, where he was an integral member of the high energy

particle physics team in search of the elusive quark. Returning to his home

state of NY, he joined the design engineering team at McGraw Edison

(later Cooper Power Systems) in Olean. During his tenure at Cooper he

was involved in the design, development and manufacturing of arresters.

He served as Engineering Manager as well as Arrester Marketing Manager

during that time. Since 2008 he has been the Principal Engineer for

ArresterWorks.

Though his entire career, Jonathan has been active in the IEEE and IEC

standard associations. He is past chair of the IEEE SPD Committee, he is

past chair of NEMA 8LA Arrester Committee, and presently co-chair of IEC

TC37 MT4. He is inventor/co-inventor on five US patents. Jonathan

received his Bachelor's degree in Electronic Engineering from The Ohio

Institute of Technology and his MBA from St. Bonaventure University.

Contact at 716-307-2431 or [email protected]


ems, 1990

Over-Voltages and the Distribution System

QUESTIONS?


ems, 1990

References

1 – http://www.picturesof.net/pages/090326-134616-923048.html

2 – www.wordy.photos/index.php?keyword=11%20kv%20fuse%20explodes&photo=0XVPcDxoV2g&category=people&title=electric+power+line+explosion

3 – http://www.satcomlimited.com/transparent_over_voltages.html

4 – http://www.hubbellpowersystems.com/cable-accessories/elbow-arresters/description/

5 – http://www.sandc.com/edocs_pdfs/edoc_024494.pdf

6 – “SURGE ARRESTER APPLICATION OF MV-CAPACITOR BANKS TO MITIGATE PROBLEMS OF SWITCHING RESTRIKES”

Lutz GEBHARDT - ABB – Switzerland, [email protected] & Bernhard RICHTER - ABB – Switzerland, [email protected]

7 – “COMPUTATION OF FAST TRANSIENT VOLTAGE DISTRIBUTION IN TRANSFORMER WINDINGS CAUSED BY VACUUM CIRCUIT

BREAKER SWITCHING”

Casimiro Álvarez-Mariño and Xosé M. López-Fernández, Dept. of Electrical Engineering, Universidade de Vigo, EEI,

Vigo, Spain, [email protected]

8 – http://new.abb.com/products/transformers/distribution

9 – http://commons.wikimedia.org/wiki/File:37.5kVA_three_phase_utility_stepdown.jpg

10 – http://uqu.edu.sa/files2/tiny_mce/plugins/filemanager/files/4310333/traveling_wave.pdf

11 – http://revistas.unal.edu.co/index.php/ingeinv/rt/printerFriendly/25218/33722

12 – http://io9.com/photos-from-the-days-when-thousands-of-cables-crowded-t-1629961917

13 – http://www.edn.com/Home/PrintView?contentItemId=4426566

14 –http://www.ecnmag.com/articles/2011/07/advanced-tvs-construction-improves-lightning-protection

15 – http://www.nautel.com/support/technical-resources/tips-n-tricks/04-09-2012/

16 – http:// www.slideshare.net

17 – https://library.e.abb.com/public/a8c42d637aa10aa2c12577ee0055faad/ABB_DPDQPole_Qpole_revB_EN.pdf

18 – http://www.cooperindustries.com/content/dam/public/powersystems/resources/library/230_PowerCapacitors/23012.pdf

19 – http://www.cooperindustries.com/content/dam/public/powersystems/resources/library/225_VoltageRegulators/MN225008EN.pdf

20 – https://www.osha.gov/SLTC/etools/electric_power/illustrated_glossary/substation_equipment/potheads.html

21 – http://ecmweb.com/archive/applying-pole-mounted-overvoltage-protection

22 – http://www.cpuc.ca.gov/gos/Resmajor/SU6/GO95/SU6_GO95_rule_54_6-F.html

Continued on Next Page


ems, 1990

References - continued

23 – http://creepypasta.wikia.com/wiki/File:5178_apocalyptic_destruction.jpg

24 – http://en.wikipedia.org/wiki/Distribution_transformer

25 – http://www.icccable.com/company_product.html?cid=208

26 – http://www.powertechlabs.com/areas-of-focus/power-labs/cable-technologies/condition-assessment-the-whole-picture/

27 – http://www.ee.washington.edu/research/seal/projects/seal_robot/sensors.html

28 – http://www.epa.gov/electricpower-sf6/documents/sf6_byproducts.pdf

29 – http://cdn2.hubspot.net/hub/272197/file-251812186-pdf/white_papers/afi-wp-transoil1.pdf

30 – http://reliabilityweb.com/index.php/print/defects_in_nonceramic_insulators_can_they_be_detected_in_a_timely_manner1

31 – http://www.inmr.com/thermal-inspection-program-finds-failing-dead-end-polymeric-insulators-2/5/

32 – http://en.wikipedia.org/wiki/Fallout_shelter

33 – http://classicconnectors.com/wp-content/uploads/2012/07/Illustration.jpg

34 – “Electrical Distribution System Protection”, 3rd Edition, Cooper Power Systems, 1990

35 – http://www.cooperindustries.com/content/public/en/power_systems/products/voltage_regulators/32-step_single-phase.html

36 – https://fisitech.wordpress.com/2010/10/22/practical-issues-switching-surgeac-transcient/

37 – http://nepsi.com/services/power-systems-studies/

38 – http://file.scirp.org/Html/3-9800140_1113.htm

39 – http://electrical-engineering-portal.com/definition-basic-insulation-level-bil

40 – http://www.schneider-electric.com/download/hk/en/details/18865768-General-Specification-for-Fixed-Capacitor-Bank-for-Electrical-Network-up-to-

36kV/?reference=Fixed_capacitor_bank_36kV_specENv2

41 – http://www.hubbellpowersystems.com/catalogs/arresters/31_optima.pdf

42 – http://www.coe.montana.edu/ee/seniordesign/archive/SP13/150mwwindfarm/Data_Content/InsulationCoordination.pdf

43 - http://electrons.wikidot.com/semiconducting-ceramics:varistor-applications

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