Transient Recovery Voltages (TRVs) for High-Voltage ... · Transient Recovery Voltages (TRVs) for...

Transient Recovery Voltages (TRVs)for High-Voltage Circuit Breakers

Part 1

Denis DufournetChair CIGRE WG A3.28 & IEEE WG C37.011, Fellow IEEE

San Antonio (USA), 19/09/2013

GRID

TRV HV Circuit Breakers P 2

Page

• Introduction & General Considerations 4 &13• Capacitive Current Switching TRV 29• Types of Fault TRVs 45• TRV Modification 63• Terminal Fault TRV 72

− First-pole-to-clear factor 73− TRV rating & testing 88− TRV & arcing times 120− TRV for generator circuit breakers 138

• Short-Line Fault TRV 148• ITRV (Initial TRV) 187

Content (1/3)


Page

• Out-of-Phase TRV 194• Three-Phase Line Faults TRV 199• Shunt Reactor Switching TRV 217• Transformer Limited Fault TRV 229• Series Reactor Limited Fault TRV 264• Influence of Series Capacitors on TRV 271• Harmonization of TRVs in IEC & IEEE 282

Content (2/3)


Page

• Annexes 306− A: First-pole-to-clear factor 307− B: Second-pole-to-clear factor 316− C: Complement on line faults 321− D: Equivalent circuit for 3-phase to ground fault 326− E: Test circuit for kpp = 1.3 329− F: Bibliography 333

Content (3/3)

Introduction

GRID


• The TRV is a decisive parameter that limits the interrupting capabilityof a circuit breaker.

• The interrupting capability of a circuit breaker was found to be stronglydependent on TRV in the 1950’s.

• When developing interrupting chambers, manufacturers must verifyand prove the TRV withstand specified in the standards for differenttest duties.

• Users must specify TRVs in accordance with their applications.

• Type tests in high-power laboratories must be performed inaccordance with international standards, in particular with rated valuesof TRVs.

Importance of TRV


1993-1996: CIGRE-CIRED WG CC03 “Medium Voltages TRVs“

1994-1998: IEC SC17A WG21 “Revision Circuit Breaker Standard”

1997-2002: IEC SC17A WG23 “Harmonization TRVs Circuit Breakers ≥ 100kV”

2002-2006: IEC SC17A WG35 “”Revision TRVs Circuit Breakers < 100kV”

2001-2009: IEEE C37-04 & 06 ”Harmonization TRVs Circuit Breakers”

2002-2005: IEEE C37-011 “Revision Application Guide HV Circuit Breakers”

2004-2008: CIGRE WG A3-19 ”Implications of Three-phase Line Faults”

2007-2009: CIGRE WG A3-22 ”Technical Requirements for UHV Equipment”

2009-2011: IEC SC17A MT36 TF ”Introduction UHV TRVs in IEC 62271-100”

2008-2011: IEEE C37-011 ”Revision Application Guide HV Circuit Breakers”

2011-2013: CIGRE WG A3-28 ”Switching Phenomena for UHV & EHV Equipment”

“Recent” TRV Studies in International Bodies

• TRV Studies by International Working Groups


• A.Greenwood, Electrical Transients in Power Systems. (book) 2nd

edition, John Wiley & Sons (1991).

• R.Alexander, D.Dufournet, IEEE Tutorial on TRVs (2003-05) http://www.ewh.ieee.org/soc/pes/switchgear/presentations/trvtutorial/TutorialTRVAlexander-Dufournet.pdf

• D.Dufournet, TRVs for High-Voltage Circuit Breakers, Presentation at IEEE Switchgear Committee meeting in Calgary (2008-10)http://www.ewh.ieee.org/soc/pes/switchgear/presentations/2008cbtutorial/Part4_IEEETutorialonTRVHVCircuitBreakers-Dufournet.pdf

• CIGRE Technical Brochure N°134, Transient Recovery Voltages in Medium Voltage Networks (1998-12)

• CIGRE Technical Brochure N°408, Line fault phenomena and theirimplications for 3-phase short and long-line fault clearing, (2010-02)

Main References


• A.Janssen, D.Dufournet, “Travelling Waves at Line Fault Clearing and Other Transient Phenomena”, CIGRE Session 2010, Paper A3-102.

• CIGRE Technical Brochure 456, “Background of TechnicalSpecifications for Substation Equipment Exceeding 800kV AC”, byCIGRE WG A3-22 (2011-04).

• D.Dufournet, A.Janssen, “Transformer Limited fault TRV”, Tutorial atIEEE Switchgear Committee Meeting in San Diego (2012-10)

Main References

• Denis Dufournet, Joanne (Jingxuan) Hu, High-Voltage CircuitBreakers Seminar Part 2 Transient Recovery Voltages, University ofManitoba, Winnipeg (2012-06)


• IEC 62271-100, High-Voltage Circuit-Breakers (2012-09)• IEC 62271-101, Synthetic testing (2012-10)• IEC 62271-110, Inductive load switching (2012-09)• IEC 62271-306, Guide to IEC 62271-100, 62271-1 .. (2012-12)• ANSI/IEEE C37.04, 04a, 04b, IEEE Standard Rating Structure for AC

High-Voltage Circuit Breakers.• IEEE Std C37.06-2009, Draft AC High-Voltage Circuit Breakers Rated on

a Symmetrical Current Basis-Preferred Ratings and Related Required Capabilities

• IEEE Std C37.09, 09b-2010, IEEE Standard Test Procedure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis.

• IEEE C37.011, Application Guide for TRV for AC High-Voltage Circuit Breakers” (2011).

• IEEE C37.013, IEEE Standard for AC High-Voltage Generator Circuit Breakers Rated on a Symmetrical Current Basis.

Standards & Guides


• In the second edition of IEC 56 published in 1954, the TRV, defined as"restriking voltage”, was of single frequency.

The amplitude factor (or crest value) and the TRV frequency (related tothe rate-of-rise) were not specified but had to be evaluated during thetests.

• In the third edition of IEC 56, published in 1971, IEC introduced for thefirst time the term “TRV” and its representation by two or fourparameters. The short-line-fault tests were also introduced in thisedition.

• TRVs requirements were also introduced in 1971 in ANSI C37.072-1971 (IEEE Std. 327), with TRV ratings in C37.0722-1971 and TRVApplication Guide C37.0721-1971 (IEEE Std. 328).

Historical Perspective


• In the fourth edition of IEC 56, published in 1987, a first-pole-to-clearfactor of 1.3 is the only factor specified for rated voltages ≥ 245 kV.

− the rate of rise of recovery voltage (RRRV) is doubled to 2.0 kV/µsfor terminal fault test duty T100.

− ITRV is introduced for rated voltages ≥ 100 kV.

• ITRV is introduced in ANSI C37.04 and C37.09 in 1991 (amendments04i and 09g).

• ANSI C37-06 (1997) harmonize partly TRV parameters with those inIEC (e.g. RRRV = 2.0 kV/µs for T100).

• As in IEC, line surge impedance is 450 Ω for all rated voltages inANSI/IEEE C37.04-1999 (instead of 450 Ω for Ur ≤ 242 kV and 360 Ωfor Ur ≥ 362 kV).



• Further Harmonization of TRVs between IEC and IEEE leadto

− Amendments 1 and 2 of IEC 62271-100 (respectively in 2002 and2006)

− Amendments of IEEE C37.04b (2008), IEEE C37.06 (2009) andIEEE C37.09b (2010).

Harmonization of IEC and IEEE standards for high-voltage circuitbreakers is presented in detail in a specific chapter.


General considerations on Transient Recovery Voltages

GRID


Xs

U

A B

Recoveryvoltage

• The recovery voltage is the voltage which appears across theterminals of a pole of circuit breaker after current interruption.

CURRENT

TRANSIENT RECOVERYVOLTAGE

RECOVERY VOLTAGE

General Considerations


• Current Interruption Process in SF6 Circuit Breakers

Two contacts areseparated in eachinterrupting chamber.An arc is generated, it iscooled and extinguishedwhen current passesthrough zero.


Simulation arc interruption


TRV

TRV (kV)I (A)

• During the interruption process, the arc loses rapidly its conductivity asthe instantaneous current approaches zero.

• During the first microseconds after current zero, the TRV withstand isfunction of the energy balance in the arc: it is the thermal phase ofinterruption.

Gas circuit breakers:Within a few microsecondsafter current zero, arcresistance (RARC) rises toone million ohm in a fewmicroseconds and currentstops flowing in the circuit.


Interruption when current passes through zero


• Later, the voltage withstand is function of the dielectric withstandbetween contacts: it is the dielectric phase of interruption.

• During type tests, standards require that the recovery voltage isapplied during 300 ms after current interruption.


The breaking operation is successful if the circuit breaker is able towithstand the TRV and the power frequency recovery voltage.

The TRV is the difference between the voltages on the source sideand on the load side of the circuit breaker.


• The nature of the TRV is dependent on the circuit being interrupted,whether primarily resistive, capacitive or inductive, (or somecombination).

• When interrupting a fault at the circuit breaker terminal (terminal fault)in an inductive circuit, the supply voltage at current zero is maximum.

The circuit breaker interrupts at current zero (at a time when the powerinput is minimum) the voltage on the supply side terminal meets thesupply voltage in a transient process called the TRV.

TRV frequency is

with L = short-circuit inductance

C = supply capacitance.

CL21


Fault


Current and TRV waveforms during interruption of inductive current

CURRENT


Supply voltage


TRV during inductive current breaking

Note: voltage polarity not respected on Figure


TRV and recovery voltage in resistive, inductive and capacitive circuits

-2

-1,5

-1

-0,5

0

0,5

1

1,5

2

2,5

0 0,005 0,01 0,015 0,02 0,025 0,03 0,035

RESISTIVE CIRCUIT

INDUCTIVE CIRCUIT (with stray capacitance)

CAPACITIVE CIRCUIT



• Combination of the former basic cases are possible, for example theTRV for mainly active load current breaking is a combination of TRVsassociated with inductive and resistive circuits.

• They are specified for high-voltage switches only as circuit-breakersare able to interrupt with more severe TRVs (in inductive circuits).



• Fault interruptions are often considered to produce the most onerousTRVs. Shunt reactor switching is one of the exceptions.

• TRVs can be oscillatory, triangular, or exponential and can occur as acombination of these forms.

• The highest peak TRVs are met during capacitive current and out-of-phase current interruption,

• TRVs associated with the highest short-circuit current are obtainedduring terminal fault and short-line-fault interruption.

• In general, a network can be reduced to a simple parallel RLC circuitfor TRV calculations.

This representation is valid for a short-time period until voltagereflections return from remote buses (see IEEE C37.011-2011)



R C

(Vcb)

L

Real network Equivalent circuit

N Lines, each with surge impedance

clZ

NZR

L: source inductance, lines exceptedC: source capacitance, lines excepted



− The TRV in the parallel RLC circuit is oscillatory (under-damped) if

− The TRV in the parallel RLC circuit is exponential (over-damped) if

CLR /21

CLR /21

R C

(Vcb)

L



0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

2

0 1 2 3 4 5 6 7 8 9

TRV (p.u.)

R / (L / C)0.5 = 10

4

2

1

0.75

0,5

0,3

t / RC


Damping of the oscillatory TRV is provided by R, as R is in parallel to L and C (parallel damping) the damping increases when the resistance decreases (the TRV peak increases when R increases).

t/RC


• Reflection from end of lines

When longer time frames areconsidered, typically several hundredsof micro-seconds, reflections on linesmust be considered.

0

100

200

300

400

500

600

700

800

900

0 100 200 300 400 500 600 700 800 900 1000

TIME (µs)

VOLTAGE (kV)

SYSTEM TRVTRV CAPABILITY FOR A STANDARD BREAKER

REFLECTED WAVE

Lines or cables must then be treated as components with distributed elements on which voltage waves travel after current interruption.

These traveling waves are reflected and refracted when reaching an open circuit or a discontinuity.



• The most severe TRV occurs across the first pole to clear of a circuitbreaker when it interrupts a three-phase terminal fault with asymmetrical current and when the system voltage is maximum (seesection on Terminal fault).

(arc resistance changes from zero to an infinite value at currentzero).


• By definition, all TRV values defined in the standards are inherent,i.e. the values that would be obtained during interruption by an idealcircuit breaker without arc voltage.

Capacitive Current Switching TRV & Recovery Voltage

GRID


-1,5

-1

-0,5

0

0,5

1

1,5

2

2,5

0,005 0,01 0,015 0,02 0,025 0,03 0,035

Recovery voltage

Supply voltage

Load voltage

U (p.u.)

Time (s)

current interruption

Example of a single phase interruption at

50 Hz

Capacitive current interruption: recovery voltage has a (1 – cos) waveshape

Capacitive Current Switching



Supply-side voltage

Load-side voltage

Recovery voltage

Current

Current interruptionContact separation

Restrike

Final current interruption


-1,5

-1

-0,5

0

0,5

1

1,5

2

2,5

3

3,5

0,005 0,01 0,015 0,02 0,025

Recovery voltage

U (p.u.)

Time (s)

instant of current interruption

Reignition Restrike

Overvoltage 3 p.u.

no overvoltage overvoltage

2 p.u.

2 p.u.



• Two cases can be distinguished, depending on when the restrike happens:

− When it is less than 1/4 of a cycle after current interruption: it is called a reignition,

no overvoltage is produced on the circuit during the transient period when the load voltage tend to reach the supply voltage.

− When it is more than 1/4 of a cycle after current interruption, it is called a restrike,

there is an overvoltage on the circuit during the transient period following the restrike.



"1-Cos" Waveshape

• Special case of series capacitor switching by by-pass switches

− By-pass switches must be able to withstand the reinsertion voltage without restrike during the transfer of reinsertion current.


− Several transient reinsertion voltagewaveshapes can be obtained in service.

− The reinsertion voltage waveshape should be determined bysystems studies.

− For standardization purposes, and in order to cover the greatestnumber of practical cases, IEC 62271-109 recommends a "1-cos"waveshape having a preferred first time-to-peak of 5,6 ms.

− A restrike happens if there is a resumption of current 2.8 ms orlater after the initial current interruption.

"1-Cos" Waveshape

• Special case of series capacitor switching by by-pass switches


Circuit with capacitive and inductivecomponents.

• The recovery voltage is the sum a 1– coswave-shape and a high-frequency voltageoscillation on the supply side due to atransient across the short-circuit(inductive) reactance at the time ofinterruption (explanation on next slide).

• There is an initial voltage jump.

• It tends to increase the minimum arcingtime and therefore to increase the shortestduration between contact separation andthe instant of peak recovery voltage.

• Interruption is easier when the voltagejump is higher

Capacitive Current SwitchingVoltage Jump

E

A


1- Supply-side voltage aftercurrent interruption, withvoltage jump2- Load-side voltage aftercurrent interruption3- Recovery voltage acrosscircuit-breaker terminals

0

Voltage beforecurrent interruption

1

Capacitive Current SwitchingVoltage Jump

2111

CLE

LC

ECC

IUs

s

A


N

A BER

ES

ET

EN

CR

CS

CT

Three-Phase Capacitive Current BreakingCapacitor Bank with Isolated Neutral


-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

-0 ,005 -0,003 -0,001 0,001 0 ,003 0,005 0,007 0 ,009 0,011 0,013 0 ,015

V B

V A

V N

2.5 p.u.


Recovery voltage for the first pole to interrupt

Due to neutral voltage shift (VN) after interruption by the first pole, the peak recovery voltage is 2.5 p.u. instead of 2 p.u. for single-phase interruption.


The recovery voltage is higher on the first pole to clear


Recovery voltage (RV) on each pole

RV on first-pole-to-clear

uc= 2.5 p.u.kc= 1.25


TRV 3-PHASE CAPACITIVE CURRENT SWITCHING (50Hz) Capacitor bank with isolated neutral

0

0,5

1

1,5

2

2,5

3

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10T (ms)

TRV

(p.u

.)

Single-phase test with kc= 1,4

Three-phase test

Single-phase test with kc= 1,25

The three-phaserecovery voltage isconsidered to becovered during asingle phase testwith a supplyvoltage equal to thephase to groundvoltage multipliedby 1.4



In the case of line switching

The recovery voltage isinfluenced by phase-to-ground and phase-to-phasecapacitances

Equivalence during single-phase test is obtained with asupply voltage equal to thephase-to-ground voltagemultiplied by a factor = 1.2(U is 2.4 p.u.).

Three-Phase Line-Charging Current Breaking


Three-Phase Cable-Charging Current Breaking

• Types of cables & equivalent circuits

Same case as capacitor bank with grounded neutral

Similar case as overhead lines

Screened cable Belted cable

C1/C0=3 Ur ≤ 52kV

C1/C0=2 Ur > 52kV


Three-Phase Capacitive Current Breaking Single-phase tests to simulate three-phase conditions

• Test voltage for single-phase tests:

• Voltage factors in case of effectively grounded neutral systems− Line-charging current kc = 1.2− Cable-charging current kc = 1.0 (screened cable)

= 1.4/ 1.2 (belted cable ≤52kV / >52kV)− Capacitor-bank current kc = 1.0/1.4 grounded/isolated neutral

• Voltage factors in case of non-effectively grounded neutral systems− Line-charging current kc = 1.4− Cable-charging current kc = 1.4− Capacitor-bank current kc = 1.4

• Voltage factors in the case of fault on another line(s)− Effectively grounded neutral systems kc = 1.4− Non-effectively grounded neutral systems kc = 1.7

3r

ctestUkU

Types of Fault TRVs

GRID


R C

(Vcb)

L

Real network Equivalent circuit

N Lines, each with surge impedance

clZ

NZR

L: source inductance, lines exceptedC: source capacitance, lines excepted

Types of Fault TRVs / Reminder


Types of Fault TRVs / Overdamped TRV

• The exponential part of a TRV occurs when the equivalent resistanceof the circuit with N connected lines in parallel

R = Zeq = is lower or equal to

where Z1 = positive sequence surge impedance of a lineZ0 = zero sequence surge impedance of a line

N = number of lines,

Leq = equivalent inductance, Ceq = equivalent capacitance.• It typically occurs when one or several lines are on the unfaulted sideof the circuit breaker and when the fault is cleared at the circuitbreaker terminals.• The rate of rise of recovery voltage is RRRV = Zeq x (di/dt)

NZ1 eqeq CL /5.0

Exponential (overdamped) TRV

01

0

23

ZZZ



• Equivalent inductance

when

• Equivalent capacitance

R C

(Vcb)

L01

10eq 2

3LL

LLL

Leq ZeqCeq

32

3)(2 1001

0eqCCCCCC

Three-phase to ground fault

see Annex D: 3-phase network representation

11

10

3.17

93

LLL

LL

eq



• Equivalent surge impedance (first pole to clear)

01

10eq 2

3ZZ

ZZN

Z

Three-phase to ground fault

3

2

10

1

0

ZZZ

ZZZZZZ

M

MS

MS

ZS: self value

ZM: mutual value

01

0

23

ZZZ

see Annex D: 3-phase network representation

See section on SLF for the calculation of line surge impedance


• TRV for parallel RLC circuit

with

ucb is the voltage across the open circuit-breaker

u1 =

= 2 f = 377 rad/s at 60 Hz and 314 rad/s at 50 Hz

I is the short-circuit current (rms)

=

=


))sinh(cosh1(1cb tteuu t

eqω2 LI

eqeq21

CZ

)/(1 eqeq2 CL


• TRV when Ceq can be neglected

where

• RRRV


)1( /1cb

teuu

eq

eq

ZL

dtdIZZI

tu

eqeqcb ω2

dd


• Special case of three-phase ungrounded faults

− Equivalent inductance

− Equivalent capacitance

with C1= C0


11

eq 5.12

3 LLL

5.132 11

eqCCC


• This exponential part of TRV is transmitted as traveling waves oneach of the transmission lines. Reflected wave(s) returning from openlines or discontinuities contribute also to the TRV.



• As an example, the following figure shows the one line diagram of a550 kV substation. The TRV seen by circuit breaker (A) when clearingthe three-phase fault is shown in the next slide. Circuit breaker (B) isopen.



0

100

200

300

400

500

600

700

800

900

0 100 200 300 400 500 600 700 800 900 1000

TIME (µs)

VOLTAGE (kV)

SYSTEM TRVTRV CAPABILITY FOR A STANDARD BREAKER

REFLECTED WAVE

A reflection occurs from the end of the shortest line after 2 x 81 / 0.3 = 540 µs

System TRV with reflected wave



• The exponential part of TRV is transmitted as traveling waves on each of the transmission lines.

• When a wave reaches a discontinuity on the line (another bus or a transformer termination) a reflected wave is produced, which travels back towards the faulted bus.

• It takes 6.67 µs for a wave to go out and back to a discontinuity 1km away as the wave travels at 300 000 km/s (speed of light).

• At a discontinuity transmitted and reflected waves can be described by the following equations:

ba

bit

2ZZ

Zee

ba

abir ZZ

ZZee

Za

Zb

Types of Fault TRVs / Reflected Waves


• A wave that reaches a short-circuit point (Zb= 0) is reflectedwith an opposite sign

• A wave that reaches an openpoint (Zb is infinite) is reflectedwith the same sign.The voltage at this point is thendoubled.

ba

bit

2ZZ

Zee

ba

abir ZZ

ZZee

ZaZb



• Example of TRV resulting from several traveling waves


From CIGRE WG A3-22/28 tutorial in Rio de Janeiro (2012-02)

Times in µs and not in ms


• An oscillatory TRV occurs generally when a fault is limited by atransformer or a series reactor and no transmission line (or cable) surgeimpedance is present to provide damping.

Types of Fault TRVs / Underdamped TRV

Oscillatory (underdamped) TRV


• To be oscillatory, the equivalent resistance of the source side has tobe such that

Leq = equivalent source inductance

Ceq = equivalent source capacitance.

• To meet this requirement, only a low number of lines (N) must beconnected on the source side.Therefore oscillatory TRVs are specified for− terminal fault test duties T10 and T30 for circuit breakers in

transmission systems (Ur 100 kV),− all terminal fault test duties in the case of circuit breakers in

distribution or sub-transmission systems (Ur < 100 kV).

eq

eqeq C

LNZR 5.0



• Transmission systems (Ur 100 kV)In the large majority of cases, TRV characteristics (peak value andrate-of-rise) for faults with 10% or 30% of rated short-circuit currentare covered by the rated values defined in the standards for testduties T10 and T30.



• Triangular-shaped TRVs are associated with short-line faults (seeseparate chapter on SLF).

• After current interruption, the line-side voltage exhibits a characteristictriangular waveshape.

• The rate-of-rise of the saw-tooth shaped TRV is function of the linesurge impedance and current. The rate-of rise is usually higher thanthat experienced with exponential or oscillatory TRVs (with the samecurrent), however the TRV peak is generally low.

line

Circuit breaker

Types of Fault TRVs / Triangular wave-shape

TRV Modification

GRID


Current Asymmetry and Circuit Breaker Influence on TRV


• When interrupting asymmetrical currents, TRV is less severe (lowerRRRV and TRV peak) than when interrupting the relatedsymmetrical current because the instantaneous value of the supplyvoltage at the time of interruption is less than the peak value.

TIME

CURRENT

SUPPLY VOLTAGE

TRV Modification / Current Asymmetry


• Correction factors of the TRV peak and rate of rise of recovery voltage(RRRV) when interrupting asymmetrical currents are given in

− IEEE C37.081 “IEEE Guide for Synthetic Fault Testing of AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis”.

− IEEE C37.081a “Supplement to IEEE Guide for Synthetic FaultTesting 8.3.2: Recovery Voltage for Terminal Faults; AsymmetricalShort-Circuit Current”.

− IEC 62271-100 “High-Voltage Circuit-Breakers” (2012-09).

− IEC 62271-101 “Synthetic testing” (2012-10): Annex I




• The RRRV is proportional to the slope of current before interruption(di/dt). Factor F1 gives the correction due to current asymmetry:

with D degree of asymmetry (p.u.)

- D interruption after a major loop of current

+ D interruption after a minor loop of current

X / R short-circuit reactance divided by resistance

• When time to peak TRV is relatively short (< 500 µs), the correctionfactor for the TRV peak is also F1.

RXDDF/

1 21



• Correction factor for the TRV peak in case of long time to peak TRV(> 500 µs) :


• During current interruption, the circuit TRV can be modified by acircuit breaker:

− by arc resistance,

− by the circuit breaker capacitance or opening resistor (if any).

• The TRV measured across the terminals of two different types ofcircuit breakers under identical conditions can be different.

• To simplify both rating and application, the power system TRV iscalculated ignoring the influence of the circuit breaker.

The circuit breaker is considered to be ideal i.e. without modifyingeffects on the electrical characteristics of a system,

− when conducting its impedance is zero,

− at current zero its impedance changes from zero to infinity.

TRV Modification / Circuit Breaker Influence


• When a circuit breaker is fitted with grading capacitors or with line-to-ground capacitors, these capacitors can reduce significantly the rate-of-rise of TRV during short-line faults.

• Opening resistors (R) are used to assist interruption by air blast circuitbreakers, they are used on some SF6 circuit breakers (Japanese550kV 1 break & 1100 kV 2 breaks).

The RRRV (rate of rise ofrecovery voltage) is reducedas follows

The resistor (R) is in parallelwith the surge impedance ofthe system (Z). Air blast Generator Circuit Breaker

with opening resistor

2IRZRZ

dtdi

RZRZ

dtdu



Interruption with Opening Resistance

Arc extinction is facilitated by reducing the voltage stress (RRRV) after current interruption, a parallel resistance is used for this purpose

R


Terminal Fault TRV

GRID


Terminal fault TRV First pole to clear factor


Current - TRV - Recovery Voltage

CURRENT


RECOVERY VOLTAGE

Terminal Fault TRV


• First Pole to Clear Factor (kpp)− During 3-phase faults interruption, the recovery voltage is higher on

the first pole to clear. − The first-pole-to clear factor is the ratio of the power frequency

voltage across the first interrupting pole, before current interruptionin the other poles, to the power frequency voltage occurring acrossthe pole after interruption in all three poles.

− It is the ratio between the recovery voltage (RV) across the first pole to clear and the phase to ground voltage of the system.

3

VoltageRecoverypp Urk

Terminal Fault TRV


• First Pole to Clear Factor (kpp)

A BER

ES

ET

3rpp

Uk

3rU

Terminal Fault TRV


• When tests are performed on one pole (single-phase tests), the supplyvoltage must be multiplied by kpp in order to have the recovery voltagethat would be met on the first pole during a three-phase interruption.

• The first–pole–to-clear factor (kpp) is a function of the groundingarrangements of the system and of the type of fault.

Note: for UHV systems (rated voltages 1100 & 1200kV) the ratio X0/X1is close to 2 and the standardized value of kpp is 1.2.

• For three-phase ungrounded faults, kpp is 1.5.

Terminal Fault TRV

For systems with non-effectively grounded neutral, kpp is 1.5.

For three-phase to ground faults in systems with effectively groundedneutral, kpp is 1.3 (see Annex A).


Three-phase faults in non-effectively grounded systems or three-phase ungrounded faults

In these cases, kpp is 1.5

Terminal Fault TRV


Terminal Fault TRV Example of First-Pole-To-Clear Factor (kpp)

3-phase ungrounded fault in effectively-grounded neutral

When pole A interrupts.

voltage eA is maximum = 1 p.u.

eB = eC = - 0.5 p.u.First-pole-to-clear

factor is 1.5

5.1)5.0(1

5.02

2

2

02

PA

CBP

CBBBP

CB

CB

ee

eee

eeedtdiLee

eedtdiL

edtdiLeL

L

Li

i


A BER

ES

ET

First-pole-to-clear factor is 1.5

When the first pole interrupts: Voltage at neutral point N:EN + ES = Xsc IEN + ET = - Xsc IEN = – (ES + ET)/2ER is maximum = Emax cos(0°) = 1 p.u.ES = Emax cos (120°) = -0.5 p.u.ET = Emax cos (240°) = -0.5 p.u.then EN = 0.5 p.u.Voltage EA = EN + ER = 1.5 p.u.

N

Xsc

Xsc

Xsc

kpp= 1.51 p.u.

Terminal Fault TRV Example of First-Pole-To-Clear Factor (kpp)

3-phase to ground fault in non-effectively grounded system


E I3

I2

I1

V3

V2

V1

Single-phase fault in an effectively grounded system

• In this case, kpp is 1.0 as the circuit breaker interrupts under the phase-to-ground voltage.

Terminal Fault TRVFirst-Pole-To-Clear Factor (kpp)


Three-phase to ground fault in effectively grounded neutral systems

• The value of kpp is dependent upon the sequence impedances from the location of the fault to the various system neutral points (ratio X0/X1).

where X0 is the zero sequence reactance of the system,

X1 the positive sequence reactance of the system.

For systems up to 800 kV, the ratio X0/X1 is taken to be 3.0.

Hence, for systems with effectively grounded systems kpp is 1.3.

Terminal Fault TRVFirst-Pole-To-Clear Factor (kpp)

01

02

3XX

Xk pp


Equations for the other clearing poles• In systems with non-effectively grounded neutral, after interruption of

the first phase (R), the current is interrupted by the last two poles inseries under the phase-to-phase voltage (ES – ET) equal to timesthe phase voltage

ER

ES

ET

I

I

ES - ET

3

Terminal Fault TRVPole-To-Clear Factor


It follows that, in systems with non-effectively grounded neutrals,for the second and third pole to clear:

87.023ppk

Current in each phase TRV in each phase


After interruption of the 3 poles, the recovery voltage is 1 p.u.


In systems with effectively grounded neutrals, the second pole clearsa three-phase to ground faultwith a factor

If X0 / X1 = 3.0 the second pole to clear factor is 1.25.10

2110

20

23

XXXXXX

k pp

Currents TRVs


See Annex B


E I3

I2

I1

V3

V2

V1

In systems with effectively grounded neutral, for the third pole-to-clear:

1ppk



Pole-to-clear factors (kp) for each clearing pole3-phase to ground case

Note: values of the pole-to-clear factor are given for X0/X1 = 1.0 toindicate the trend in the special case of networks with a ratio X0/X1 ofless than 3.0.

kpp= 1.5 is taken for all systems that are not effectively grounded, itincludes (but is not limited to) systems with isolated neutral (it is alsotaken for three-phase ungrounded faults).

Neutral X0/X1

first pole 2nd pole 3rd pole

isolated infinite 1.5 0.87 0.87

effectivelygrounded 3.0 1.3 1.27 1.0

see note 1.0 1.0 1.0 1.0

Pole to clear factor



Terminal fault TRV Rating & Testing


CURRENT


Supply voltage

Terminal Fault TRV Rating

Current

Transient recovery voltage

Supply voltage


• The TRV ratings for circuit breakers are applicable for interruptionof three-phase faults with− a rated symmetrical short circuit current− at the rated voltage of the circuit breaker.

• In IEC− While three-phase ungrounded faults produce the highest TRV

peaks, the probability of their occurrence is very low.Therefore, in IEC 62271-100 the TRV ratings are based onthree-phase to ground faults.

− TRV parameters are given in subclause 4.102 of IEC 62271-100.

− For values of fault current other than rated and for line faults,related TRV capabilities are given in subclause 6.104.5 of IEC62271-100.



• In ANSI/IEEE− TRV withstand capabilities are given in ANSI/IEEE C37.04 and

IEEE C37.06.− In the case of terminal faults, for circuit-breakers of rated

voltages equal or higher than 100 kV, separate Tables giveTRVs for three-phase to ground and three-phase ungroundedfaults.



• ANSI/IEEE C37.06 – Table 10



• ANSI/IEEE C37.06 – Table 11



• For circuit breakers applied on systems 72.5 kV and below, the TRVratings assume that the system neutrals can be non-effectivelygrounded.

• For circuit breakers applied on systems 245 kV and above, the TRVratings assume that the system neutrals are effectively grounded.

• Standard TRV are defined by two-parameter and four-parameterenvelopes.

• These envelopes are used to compare

− System TRVs

− Standard TRVs

− Test TRVs




• A two-parameter envelope is used for oscillatory (underdamped)TRVs specified in standards for:

− circuit breakers rated less than 100 kV, at all values of breakingcurrent,

− circuit breakers rated 100 kV and above if the short-circuitcurrent is equal or less than 30% of the rated breaking current.

3/'

23

c

afppr

c

uu

kkUu

),2(05.0),1(15.0

3

3

systemslineSClassttsystemscableSClasstt

d

d

The test TRV must not cross the delay segment defined by (td , 0) and (t’, u’)


• A four-parameter envelope is specified for circuit breakers rated 100 kVand above if the short-circuit current is more than 30% of the ratedbreaking current (cases with over-damped TRVs).

1211 42/'23

75.023

ttuukkUukUu afppr

cppr



The peak value of TRV is defined as follows:

where

kpp is the first pole to clear factor

kaf is the amplitude factor (ratio between the peak value of TRV andthe peak value of the recovery voltage at power frequency).

In IEC 62271-100 and IEEE C37.04, kaf is 1.4 at 100% rated breakingcurrent.

32 r

ppafcUkkU



TRV envelopes for terminal fault (Ur < 100 kV)

I is the rated short-circuit current TIME

VOLTAGE

1.0 I0.6 I0.3 I0.1 I

Terminal Fault TRV Rating - Ur < 100 kV


• Cable systems and line systemsIn order to cover all types of networks (distribution, industrial and sub-transmission) and for standardization purposes, two types of systemsare introduced:− Cable systems

Cable systems have a TRV during breaking of terminal fault at100% of short-circuit breaking current that does not exceed theenvelope derived from Table 24 in Edition 1.2 of IEC 62271-100.TRV values are those defined in the former editions of IECstandard for high-voltage circuit breakers.

− Line systemsLine systems have a TRV during breaking of terminal fault at 100% of short-circuit breaking current defined by the envelope derived from Table 25 in Edition 1.2 of IEC 62271-100. Standard values of TRVs for line systems are those defined in ANSI/IEEE C37.06 for outdoor circuit-breakers.



• Comparison of TRVs for cable systems and line-systems

The rate of rise of recovery voltage (RRRV) for line systems is approximately twice the value for cable systems

Envelope of Cable system TRV

Envelope of Line system TRV

t3

Uc



• Classes of Circuit breakersCircuit breaker Ur < 100 kV

Cable-system

Line-system

Cable-system

Direct connection to OH line

SLF ?

No

Yes

YesDirect connection

to OH line

Class CS

Class LS

Class LS

Class S1

Class S2

Class S2Short-line fault breaking performance is required only for class S2



1,2

1,3

1,4

1,5

1,6

1,7

1,8

1,9

Am

plitu

de fa

ctor

(p.u

.)

T10 T30 T60 T100

Amplitude factor for terminal fault (Ur < 100 kV) Class S2 circuit breakers

10% I 30% I 60% I 100% I



0,4

0,6

0,8

1

1,2

1,4

1,6

12,5 22,5 32,5 42,5 52,5 62,5 72,5

RRRV for terminal fault T100 (Ur < 100 kV) Class S2 circuit breakers


RRRV (kV/µs)

Ur(kV)

15kV24kV

38kV

52kV

72.5kV1.47

1.33

1.21

1.05

0.91



• Calculation of standard RRRV: circuit breaker 72.5 kV class S2

− Time to peak TRV was taken from ANSI C37.06:

− Time t3 is 88% of T2 (1-COS waveshape): t3 = 93 µs

− TRV peak uc is calculated from Ur, kpp and kaf

− RRRV is the ratio of uc and t3 :

it is the present value in IEC and IEEE standards.

kVuc 1373

25.7254.15.1

µskVVATR /47.193

137

µsT 1062


0,4

0,6

0,8

1

1,2

1,4

1,6

12,5 22,5 32,5 42,5 52,5 62,5 72,5

RRRV for terminal fault T100 (Ur < 100 kV) Class S2 circuit breakers


RRRV (kV/µs)

Ur(kV)

305.04.0 rURRRV

15kV24kV

38kV

52kV

72.5kV1.47

1.33

1.21

1.05

0.91

20kV

1kV/µs



• RRRV at reduced short-circuit current (Class S2)

− Time t3 for T100 is multiplied by the following factors

0.67 for T60

0.40 for T30 and T10

− Compared with the standard value for T100, the RRRV atreduced short-circuit current is divided by the multiplier for timet3 and multiplied by the increase of amplitude factor.

− Example: T60 72.5 kV

µskVRRRV /35.254.165.1

67.047.1


TRV envelopes for terminal fault (Ur 100 kV)

I is the rated short-circuit currentNote: time to peak for T60 is shown here according to IEEE, it is half the IEC value

Terminal Fault TRV Rating - Ur ≥ 100 kV


Amplitude factor for terminal fault (Ur 100 kV) according to IEC and IEEE C37.06


1

1,1

1,2

1,3

1,4

1,5

1,6

1,7

1,8

10 20 30 40 50 60 70 80 90 100

IEEE k pp=1.5

IEC & IEEE k pp=1.3kaf (p.u.)

% Isc

Case 10 % Isc: kpp x kaf = 2.46 (IEEE kpp=1.5) and 2.29 (IEC & IEEE kpp=1.3)


Rate-of-rise-of-recovery-voltage for terminal fault(Ur 100 kV)

1

2

3

4

5

6

7

8

RR

RV

(kV/

µs)

T10 T30 T60 T100



• A circuit breaker TRV capability is considered to be sufficient if the twoor four parameter envelope drawn with rated parameters is equal orhigher than the two or four parameter envelope of the system TRV.

System TRV envelope

Circuit breaker rated TRV envelope

time

Voltage

Terminal Fault TRVApplication


• The parameters that define the circuit breaker TRV capabilities varywith the circuit breaker voltage rating and short-circuit currentinterrupting level.

• The circuit breaker TRV capabilities at 10%, 30%, 60% and 100% ofrated short-circuit interrupting current (Isc), corresponding to terminalfault test duties T10, T30, T60 and T100, are given in IEEE StdC37.06.

• The circuit breaker TRV withstand capability envelope at any othershort-circuit interrupting current below rated can be derived using themultipliers given in Table 1 of IEEE C37.011-011.

• TRV studies are sometimes carried out to determine if a system TRVis covered by the circuit breaker TRV capability demonstrated by typetests, either when new circuit breakers are to be installed or followinga system change.



• It is not uncommon that the maximum short-circuit current falls inbetween 30% and 60% of the circuit breaker rated short-circuit current.

• To allow comparison of system TRV and circuit breaker TRV withstandcapability and to avoid additional testing, a method of interpolation ofTRV capabilities demonstrated by type tests was introduced in theformer editions of IEEE C37.011.

• Following the introduction of the two-parameter and four-parameterdescription of TRVs, this method of interpolation in the current rangebetween T30 and T60 (terminal faults with respectively 30% and 60%of Isc) was not clearly stated in the 2005 edition of IEEE C37.011.

• Thus, the method of interpolation has been further developed in IEEEC37.011-2011 to define the circuit breaker TRV withstand capability forshort-circuit currents in this range between T30 and T60.



• In standards, it is considered that 30 % of Isc is the maximum short-circuit current for which a two parameter TRV is applicable for circuitbreakers rated 100 kV and above.

• The related TRV capability for short-circuit currents between 30 % of Iscand 60 % of Isc is then necessarily a four parameter TRV.

• The Working Group in charge of IEEE Guide C37.011 has defined thatthe TRV capability between T30 and T60 can be considered to have arate-of-rise (u1/t1) and a first reference voltage (u1) that haveintermediate values between those of T30 and T60.



• TRV parameters (u1, t1, uc, t2) for any terminal fault current between 30 % and 60 % of Isc can be obtained as follows:

− u1 and t1 are linearly interpolated between u1 and t1 of T60 and ucand t3 of T30

− uc and t2 are linearly interpolated between uc and t2 of T60 and ucand t3 of T30

• The method of interpolation is illustrated by the Figure shown on the next slide.




245kV Breaker TRV Envelope

0

50

100

150

200

250

300

350

400

450

500

0 50 100 150 200 250

Time (µs)

kV

T100

T75

T60

T55

T50

T45

T40

T35

T30

T10

u1,t1

Example of TRV interpolation for a 245kV circuit breaker


* When the system TRV has an initial slope that is higher than the valuespecified for terminal fault type tests, Guide IEEE C37.011 authorizesto combine the TRV withstands demonstrated during terminal fault andshort-line-fault (same range of currents).


Voltage withstand by a 550kV circuit breaker at 75% rated breaking capability


• Tests are required at 100% (T100), 60% (T60), 30% (T30) and 10% (T10) of rated short-circuit current with the corresponding rated TRVs and recovery voltages.

• In IEC 62271-100, 3 tests are required with a symmetrical current for each test duty, except T100 that is performed as follows− 3 tests with symmetrical current and− 3 tests with asymmetrical current (when interrupting asymmetrical

currents, the rate-of-rise and peak value of TRV are reduced but the energy in the arc is higher).

• In IEEE Std C37.09− for each test duty T10, T30, T60: 2 tests are required with

symmetrical current and 1 test with asymmetrical current.− test duty T100 is performed as in IEC

Terminal Fault TRVTesting


• During testing, the envelope of the test TRV (in red) must be equal or higher than the specified TRV envelope (in blue).

This procedure is justified as it allows to compare TRVs in the tworegions where a restrike is likely: during the initial part of the TRV wherethe RRRV is maximum and in the vicinity of the peak voltage (uc).

U(kV)

t (µs)t2t1

uc

u1

u'

t'

Reference line of specified TRV

Envelope of prospective test TRV

Prospective test TRV

Delay line of specified TRV

0 td

A

B

C

Terminal Fault TRVTesting


• In a network, the initial part of the TRV may have a high-frequencyoscillation of small amplitude.

• This ITRV (Initial Transient Recovery Voltage) is due to reflectionsfrom the first major discontinuity along the busbar.

• It may influence the thermal phase of interruption.

• In most cases the ITRV withstand capability is proven during short-line-fault tests.

Terminal Fault TRVInitial TRV

More information is given in the chapter dedicated to ITRV


Terminal fault TRV & Arcing Times


Arcing time

-1,5

-1

-0,5

0

0,5

1

1,5

0 0,005 0,01 0,015 0,02 0,025 0,03 0,035 0,04 0,045 0,05

Contacts separation

Time

Interruption at 2nd passage through zero

1st passage through zero

Arcing time = 13 ms

Current

Terminal Fault TRV & Arcing Time


Terminal Fault TRV & Arcing Times

In the case of periodicphenomena, durationscan be expressed inmilliseconds or inelectrical degrees.For a system frequencyof 50 Hz, the duration ofone half loop is 10 ms, itcorresponds to 180° el., itfollows that 18° el. = 1ms

For a system frequencyof 60 Hz the duration ofone half loop is 8.33 msso 18° el. = 0.83 ms

-1,5

-1

-0,5

0

0,5

1

1,5

0 0,002 0,004 0,006 0,008 0,01 0,012 0,014 0,016 0,018 0,02

One period at 50 Hz

10 ms


Contacts separation

1st pole clears

last poles clear

Arcing time 1st pole

Arcing time last poles


Current

One period (360°) at 60Hz is 16.7 ms

One period (360°) at 50Hz is 20 ms


Minimum & Maximum Arcing Times

• Case 1: Reference case with contact separation at 29.67ms

Arcing time pole 3 = 8.4ms (minimum arcing time)

Example three-phase fault interruption

Fr = 50 Hz

Pole 3 interrupts first

System with non-effectively grounded neutral



• Case 2: Contact separation advanced by 3.33ms (60°) = 26.34ms

Arcing time pole 1 = 8.4ms

Pole 1 interrupts first with the same arcing time as in Case 1 by pole 3

i.e. same breaking conditions in terms of arcing times



• Case 3: Contact separation advanced by 2.33ms (42°) = 27.34ms

Pole 3 interrupts first with the longest arcing time for a first pole to clearArcing time pole 3 = 10.7ms = 8.4ms + 42°

Arcing time pole 1 = 15.7ms= 8.4ms + 7.3ms= 8.4ms + 132°maximum arcing time

The range of arcing times for the first pole to clear is 42°



Example with fr = 50 HzThree-phase faults in non-effectivelygrounded systems or three-phaseungrounded faults

-50000

-40000

-30000

-20000

-10000

0

10000

20000

0 5 10 15 20 25 30 35 40

Time (ms)

Cur

rent

(A)

Iarc

Iarc

Contact separation

Contact separation

tarc min = 12 ms

tarc max = 19,33 ms

18°

-50000

-40000

-30000

-20000

-10000

0

10000

20000

0 5 10 15 20 25 30 35 40

Time (ms)

Cur

rent

(A)

Iarc

Iarc

Contact separation

Contact separation

tarc min = 12 ms

tarc max = 19,33 ms

18°


Minimum arcing time (blue phase) Tmin = 12 ms

Contact separation delayed by 18° el. (or 1 ms)

Maximum arcing time (blue phase) = 19.33 ms(14.33 ms + 90°= Tmin + 132°)

Arcing time 1st phase (red phase) = 14.33 ms(Tmin + 60° - 18°

= Tmin + 42°)

-20000

-15000

-10000

-5000

0

5000

10000

15000

200000 5 10 15 20 25 30 35 40

time [ms]

curr

ent [

A]

18° el.

-20000

-15000

-10000

-5000

0

5000

10000

15000

200000 5 10 15 20 25 30 35 40

time [ms]

curr

ent [

A]

Three-phase faults in non-effectively grounded systems orthree-phase ungrounded faultsTmin = 12 ms

T max = 19.33 ms

Contact separation

Iarc

Iarc

Contact separation

Minimum & Maximum Arcing Times (50Hz)


-20000

-15000

-10000

-5000

0

5000

10000

15000

200000 5 10 15 20 25 30 35 40

time [ms]

curr

ent [

A]

-20000

-15000

-10000

-5000

0

5000

10000

15000

200000 5 10 15 20 25 30 35 40

time [ms]

curr

ent [

A]

Minimum arcing time (blue phase) Tmin = 12 ms

Contact separation delayed by 18° el. (or 0.83 ms)18° el.

Maximum arcing time (blue phase) = 18.1 ms

(13.94 ms + 90°= Tmin + 132°)

Arcing time 1st phase (red phase) = 13.94 ms(Tmin + 60° - 18°

= Tmin + 42°)

Three-phase faults in non-effectively grounded systems orthree-phase ungrounded faults

Tmin = 12 ms

T max = 18.1 ms

Contact separation

Iarc

Iarc

Contact separation

Minimum & Maximum Arcing Times (60Hz)

Breaking Tests HV Circuit-Breakers – Denis Dufournet

Three-phase fault in network with isolated neutral (Ur < 245kV)

A BER

ES

ET

Interruption of current in a first pole, followed ¼ cycle later by interruption of the two other poles in series

Terminal Fault Arcing timesThree-Phase Short-Circuit Current Interruption

Current

Time

Contact separation

Breaking Tests HV Circuit-Breakers – Denis Dufournet

Three-phase fault in network with effectively grounded neutral (Ur ≥ 245kV)

A BER

ES

ET

The three poles interrupt at separate current zeros withdifferent arcing times

CurrentsVoltages

Terminal Fault Arcing TimesThree-Phase Short-Circuit Current Interruption

Contact separation


Three-phase faults innon-effectively groundedsystems or three-phaseungrounded faults

Three-phase faults ineffectively groundedsystems

Currents TRVs (pole factor)

1.5

0.87

0.87

1.3

1.27

1.0

90°

120°

Maximum arcing time= Tmin + 132°

= Tmin + 6.1 ms


= Tmin + 7.5 ms

Arcing Times and TRVs / Fr = 60 Hz


Three-phase faults innon-effectively groundedsystems or three-phaseungrounded faults

Three-phase faults ineffectively groundedsystems

Currents TRVs (pole factor)

1.5

0.87

0.87

1.3

1.27

1.0

90°

120°


= Tmin + 7.3 ms

Maximum arcing time= Tmin + 162°= Tmin + 9 ms

Arcing Times and TRVs / Fr = 50 Hz


Minimum arcing time + 180° -18°


° el.


Arcing time

Reference = Minimum arcing time first pole


Reference = Minimum arcing time first pole to clear


° el.ms

Terminal Fault TRV & Arcing Times at 60Hz

Arcing time

7.55.53.55 6.14.151.95

Arcing times in ms FR = 60 Hz

0

5.55


Minimum arcing time + 180° -18°Reference = Minimum arcing time first pole

Single-phase "umbrella" test with kpp=1.3

Increased stress


° el.



Single-phase tests with minimum & maximum arcing time

-1,5

-1

-0,5

0

0,5

1

1,5

0 0,005 0,01 0,015 0,02 0,025 0,03 0,035 0,04 0,045 0,05

Contacts separation

Time

Minimum arcing time = 13 ms

Current

-1,5

-1

-0,5

0

0,5

1

1,5

0 0,005 0,01 0,015 0,02 0,025 0,03 0,035 0,04 0,045 0,05

Contacts separation

Time

restrike with arcing time 12 ms

Mximum arcing time = 22 ms= 13 ms + 10 ms - 1 ms = 13ms + 180° el. - 18° el.

Current


Example with F=50Hz


Terminal Fault TRVGenerator Circuit Breakers


• Special TRV requirements are applicable for generator circuit breakers installed between a generator and a transformer.

• Two types of faults need to be considered

A1 System-source fault B1 Generator-source fault

Generator Circuit Breakers TRV


• For the two types of fault, the TRV has an oscillatory waveshape andthe first-pole-to-clear factor is 1.5 in order to cover three-phaseungrounded faults.

• TRV parameters, i.e. peak voltage uc, rate-of-rise (RRRV) and timedelay, are listed in ANSI/IEEE C37.013.

TRV for system-source faults• RRRV for system-source faults is 3 to 5 times higher than the value

specified for distribution or sub-transmission circuit breakers ANSI/IEEEC37.04.This is due to the fact that the TRV frequency is dominated by thenatural frequency of the step-up transformer.

• IEEE has defined TRV parameters in several ranges of transformerrated power.



• TRV parameters for System-Source FaultsTable 5a– TRV parameters for system - source faults

Inherent TRVTransformer

Rating T2 -Time to - Peak E2 -Peak Voltage TRV Rate

(MVA) (µs) (kV) (kV / µs)

Line Column 1 Column 2 Column 3 Column 4

1 10 - 50 0.68 V 1.84 V 3.2

2 51 - 100 0.62 V 1.84 V 3.5

3 101 - 200 0.54 V 1.84 V 4.0

4 201 - 400 0.48 V 1.84 V 4.5

5 401 - 600 0.43 V 1.84 V 5.0

6 601 - 1000 0.39 V 1.84 V 5.5

7 1001 or more 0.36 V 1.84 V 6.0




• TRV for system-source faults (Cont’d)In IEEE C37.013-1993, the WG introduced time t3 (coming from IEC) todefine precisely the determination of the TRV rate.

E2 is equal to 1.84 V where V is the rms value of the rated maximum voltage and the value 1.84 is equal to

x 1.5 (= first-pole-to-clear-

factor) x 1.5 (= amplitude factor)32

rateTRVEtT

85.085.023

2


TRV for system-source faults (Cont’d)• The RRRV can be significantly reduced if a capacitor is installed

between the circuit breaker and the transformer. It is also reduced inthe special cases where the connection between the circuit breakerand the transformer(s) is made by cable(s) [29].

TRV RATE FOR SYSTEM FED FAULTS TRANSFORMER 50MVA<<=100MVA

2

2,2

2,4

2,6

2,8

3

3,2

3,4

3,6

0 2000 4000 6000 8000 10000 12000

CABLE CAPACITANCE (pF)

TRV

RA

TE (k

V/µs

)

100MVA81MVA

65,5MVA



TRV for system-source faults (Cont’d) • When a capacitance is added between the circuit breaker and the

step-up transformer, the TRV peak is increased (explanation: seegeneral considerations).


TRV peak increase (p.u.)

Capacitance (pF)

E2 MULTIPLIER FOR SYSTEM FED FAULTS TRANSFORMER 50MVA<<=100MVA

1

1,05

1,1

1,15

1,2

1,25

1,3

0 2000 4000 6000 8000 10000 12000

CABLE CAPACITANCE (pF)

E2 M

ULT

IPLI

ER (p

.u.)

100 MVA

81 MVA

65.5 MVA



• TRV for generator-source faults

RRRV for generator-source faults is roughly 2 times the valuesspecified for distribution or sub-transmission circuit breakers.

“Table 6a – TRV parameters for generator - source faults

Inherent TRVGenerator

Rating T2 -Time - to – Peak E2 -Peak Voltage TRV Rate

(MVA) (µs) (kV) (kV / µs)

Line Column 1 Column 2 Column 3 Column 4

1 10 - 50 1.44 V 1.84 V 1.5

2 51 - 100 1.35 V 1.84 V 1.6

3 101 - 400 1.20 V 1.84 V 1.8

4 401 - 800 1.08 V 1.84 V 2.0

5 801 or more 0.98 V 1.84 V 2.2


• TRV in case of asymmetrical currents

− Due to the large time constants of generators and transformers(high X/R), generator circuit breakers are required to interruptcurrents with a high percentage of dc component (high asymmetry).

− The rate-of rise and peak value of TRV during interruption ofcurrents with large asymmetry are significantly reduced.

− In this case, the stress is mainly due to the current amplitude andthe energy in the arc (mechanical and thermal stresses), and to alesser extent to the TRV.

− The more severe TRV stress is obtained during interruption ofsymmetrical currents.



• First-pole-to-clear factor− Effectively earthed systems kpp = 1.3 (1.2 for UHV)− Non-effectively earthed systems kpp = 1.5

• Rating− TRV with 2 or 4 parameters− Classes S1 and S2 for rated voltages < 100 kV

• Testing circuit breakers ≥ 100 kV− RRRV: 7 – 5 – 3 – 2 kV/µs for resp. T10, T30, T60, T100s− Interrupting window: 162° (kpp = 1.3) or 132° (kpp = 1.5)

• Generator circuit breakers higher RRRV for T100s

Terminal Fault TRV / Summary


Short-Line-Fault (SLF)


• The severity of SLF with its associated very fast rate-of-rise-of-recovery-voltage (RRRV) was identified at the end of the 1950’s.

• First SLF tests were performed in 1956-1958 in the USA (G.E.), alsoat Mettlen substation (CH), Fontenay (EDF High Power Laboratories)and CESI. The aim was to compare theoretical studies andexperiments.

• The first published paper on SLF is considered to be by W.F. Skeats,C.H. Titus, W.R. Wilson (G.E.) in Transactions AIEE, submitted inApril 1957 and published in February 1958.

• In Europe, a paper by Michel Pouard (EDF) was published in theBulletin de la Société Française des Electriciens in Nov. 1958.

Introduction


Introduction

Paper in Power Apparatus andSystems, Part III, Transactions ofthe American Institute ofElectrical Engineers. Publicationin February 1958

Test laboratory line used by GeneralElectric in 1957 to test air-blastcircuit-breakers. It was 1.6km long,short-circuit power of the source was50kA under 31kV.


• During the general meetings of CIGRE, SLF was first mentionedduring the session of 1958.

Two reports were presented during the CIGRE session of 1960 (byFrance and Switzerland).

• IEC introduced for the first time short-line-fault (SLF) requirementsin 1971.

• SLF TRVs were introduced also in ANSI/IEEE C37.072 in 1971.

Introduction


• The requirement of a SLF interrupting capability had and still has agreat influence on the design of high-voltage circuit breakers.

It was already the case with air blast type that had to be fitted withopening resistors for SLF interruption.

• SLF is also a critical test duty for SF6 type circuit breakers.

Sufficient pressure build-up and mass flow rate are necessary for SF6circuit breakers to interrupt at current zero.

Introduction


• Short-line faults occur from a few hundred meters up to severalkilometers down the line.− L90: short-line fault with 90% of rated short-circuit current− L75: short-line fault with 75% of rated short-circuit current

• After current interruption, the line-side voltage exhibits a characteristictriangular waveshape.

line

Circuit breaker


U

TRV, neglecting the contribution from the supply-side


• The circuit-breaker interrupts the current, at a passage through zero,the supply voltage and the di/dt are both maximum (in amplitude). Thevoltage on the circuit-breaker terminals (U0) is a fraction of the supplyvoltage Us0.

line

Line sideVoltage (point C)

Supply sideVoltage (point B)

At the time of interruptionUs0 = (LS + LL ) di/dt

U0 = LL di/dt

where di/dt is the current derivative at current zero

Example Ur = 245kV

LLLS

Us0

U0

U0

kVUUL

kVUU

s

rs

20100901:90

2003

2

00

0



• As the TRV is at high frequency, the line must be treated as atransmission line with distributed elements.

• The line side voltage oscillates as travelling waves are transmitted withpositive and negative reflections at the open breaker and at the fault,respectively.


After current interruption

The supply voltage varies much more slowly than the line-side voltage

The TRV is mainly due to the voltage variation on the line side.

Supply sidevoltage (point B)

Line-sidevoltage (point C)


• Supply-side and line-side voltages

Um: supply voltage at the time of interruptionUo: voltage on circuit breaker terminals at the time of interruptionExample L75: Ur = 245kV : Um= 200 kV, Uo= 50 kV, UL= 80 kV

Current

Supply-side voltage

Line-side voltageUo

Um

U = 0UL

t

t



SLF / Evolution of Line Voltage

Voltage profile at current zero (t=0), Voltage decreases linearly towards 0 at the fault pointIt is considered to be sum of two voltage waves moving in opposite directions.TL = Travel time for wave to travel from one end of line to the other and back.


Traveling waves thatreach the fault point arereflected with an oppositepolarity.

Traveling waves thatreach the open point, atthe circuit breakerterminal, are reflectedwith the same polarity.

Voltage at any locationon the line is the sum ofeach component.



Voltage on the line after current interruption


Voltage at circuit-breakerTerminal x = 0

Voltage half-wayto the fault x = 0.5 L

Voltage at x = 0.75 L

TIME

VOLTAGE (p.u.)

0

2

- 2

tL0.5 tL tL/4 3 tL/4 1.5 tL


Voltage on Circuit Breaker line-side terminal

-1,5

-1

-0,5

0

0,5

1

1,5

0 0,25 0,5 0,75 1 1,25 1,5 1,75 2

Line side Voltage(p.u.)

Time / TL


Damping is neglected, in practice at time TL voltage is -0.6 to -0.8 p.u.


Supply voltage

Line voltage

TRV

SLF TRV

Voltage (kV)

Time (µs)


SLF / RRRV

• The rate-of-rise of recovery voltage (RRRV) on the line side is function of the slope of current before interruption and of the surge impedance of the line:

Z is the surge impedance of the line (450 ohm)

L and C are respectively the self inductance and the capacitance of the line per unit length

I fault current (kA)

ω pulsation

s multiplier = 0.20 (f = 50Hz) or 0.24 (f = 60 Hz), du/dt in kV/µs

CLZ

IsIZdtdiZ

dtduRRRV 2

6102.0250 ZHzat


SLF / Line Surge Impedance

• Assumptions: conductors of infinite length, the electrical field and magnetic field do not penetrate the ground.

• Self surge impedance D = 2 h with h = height of line r = radius of conductorLn = natural logarithm µ0 = magnetic constant = 4π×10−7 H/m

= electric constant = 8.854×10−12 F/m

with (1)

• Mutual surge impedance (ZM) between 2 conductors is given by (1) where D isthe distance between one conductor and the image of the other conductor, and rrepresents the distance between the two conductors (see next slide).

• A matrix equation is done in case of multi-conductors circuits with self andmutual couplings. Modal analysis done by digital calculations gives the relevantmodes of travelling waves (see Annex C in [39] and [47]).

rhLn

rDLn

CLZ 26060



• Distances to consider for mutual surge impedance calculation

d12

D12

Ground

Image of bundle of conductors 2

Bundle 1

Bundle 2

Bundle 3

12

1212 60

dDLnZM



• Factors that influence the surge impedance− Geometry of a conductor

− Arrangement of the conductors in relation to the towers and the ground(single or double circuits..)

− Frequency of the TRV: Z decreases by 4% when the frequency increasesfrom 1 to 100 kHz.

− In case of bundled conductors, they can clash if the current is high enough.The surge impedance is higher after conductor clashing and reach thevalue for a single conductor: 450 Ω.

− Line height: the surge impedance of lines increases with the conductorheight above ground.

− Earth resistivity: the surge impedance increases by 5.7% at 1kHz and3.2% at 100 kHz when earth resistivity changes from 10 to 1000 Ω-m.

− Tower footing resistance: if it rises from 0 to 10 Ω the surge impedanceincreases by about 2%.


Short-line-fault

• Percentage of SLF (or M)

S

LGS X

VI LS

LGL XX

VI


• The transmission line parameters are given in terms of the effective surge impedance ( Zeff) of the faulted line and a peak factor (d)

XL is the line reactance per unit lengthv is the velocity of light (0.3 km/µs), is the line length is 2 system power frequency (314 or 377 rad/s for 50 or 60 Hz)

vXZ

dL

eff2vdtdiZu effL /2/

2LLo IXu

uLuO

O

L

uud

Short-line-fault


SLF / Voltage at Current Zero

U0

SSL

LS

S

SL

SSS

LL

XMXXMorXX

XM

IMIIXUIXU

0

SSS

SSS

SL

UMIXMUIXMXU

IMXU

110

0

0

SUMU 10

US


• The rated values for the line surge impedance Z and the peak factord are defined in standards as follows:

• The line side voltage contribution to TRV is defined as a triangularwave as follows (where IS is the rated short-circuit current) :

the first peak UL decreases when M increasesthe rate-of-rise of recovery voltage increases with M

• There is a critical value of the short-line-fault current for which thecircuit breaker has more difficulty to interrupt.

• The critical value of M is close to 90% for SF6 circuit breakers(generally in the range 90%-95%). it is between 75% and 80% forair blast circuit breakers.

rL UMU32)1(6.1

6.1/450 0 UUdZ L

2SIMZdtdiZ

dtdu

SLF / Line-side Contribution to TRV


• The following Table gives the comparison of current and voltagestresses during test duties L90 and L75, respectively at 90% and 75%of rated short-circuit current, for a circuit-breaker 245kV 40kA 50Hz.

• The current and RRRV are higher during L90, but the (first) peakvoltage is higher during L75.

• In practice, L90 is usually the most severe test duty.

RRRV: rate of rise of recovery voltage UL= first peak voltageVoltage on the line side only is considered

L90 L75

Current (kA) 36 30

RRRV (kV/µs) 7.2 6

UL (kV) 32 80

Short-line-fault


Ur = 245kV

Isc = 40kA

fr = 50Hz

0

20

40

60

80

100

120

140

0 5 10 15 20 25 30 35

T (µs)

U (k

V)

7.2 kV/µs

6 kV/µs

4.8 kV/µs

L90

L75

L60

When current decreases (longer line), the slope decreases but the peakvalue increases. It is generally considered that for SF6 circuit breakersinterruption is more influenced by the voltage slope (RRRV).

SLF / Comparison of Test Duties


• The TRV seen by the circuit breaker is the sum of a contributionfrom the line side (eL) and a contribution from the supply side (eS):

with (in a first approximation)

where

2 M = RRRV (T100) x M = 2 kV/µs x M

TL is the time to peak of the line side TRV

td is the time delay of TRV on the source side

SL eee

)(2 dLS tTMe

Short-line-fault


• Example of calculation of SLF TRV : L90 245 kV 50 kA 50 HzFault current = 0.9 x 50 = 45 kA (assuming time delay tdL= 0 µs)

Short-line-fault


• This rate-of-rise of TRV during SLF is much higher than the valuesthat are met during terminal fault interruption:

Test duty RRRV (kV/µs)

I(kA)

F(Hz)

SLFL90 50 kA 10.8 45 60

SLFL90 50 kA 9 45 50

SLFL90 40 kA 8.64 36 60

Terminal faultT60 3 30 50/60

Terminal faultT100 2 50 50/60

For SLF, this table gives the RRRV of the line side voltage

Short-line-fault


• Standard values of lines characteristics for SLF

SLF / Line Characteristics

IEC values are shown, ANSI/IEEE values cover rated voltages up to 800kV


Short-Line-FaultInfluence of an Additional Capacitor


• The SLF performance can be increased by adding a capacitor, either between terminals or phase to ground (see figure).

• A capacitor has two effects:− it decreases the oscillation frequency and the RRRV of the line

side contribution to TRV;− it increases the time delay of the line side contribution to TRV.

VLG

XS XLC.B.

SLF / Influence of an Additional Capacitor


(f ile t r v2 .pl4 ; x- var t ) v :P 0 0 v :P 1 v :P 4 v :P 1 0 0 4 8 1 2 1 6 2 0[ u s]

0

1 0

2 0

3 0

4 0

5 0

6 0

[ kV ]

TRV without capacitor

TRV with capacitor(capacitance increase from 1 to 3)

1 2 3



− Equation of the line-side contribution to TRV up to the first peak:

− If the capacitor is connected phase to ground on the line side, the reduction of the line side RRRV can be estimated by a simple calculation, as detailed in the next slide, withCadd additional line-to-ground capacitance;

L line inductance;

Z line surge impedance;

CL total line capacitance = L/Z2;

Ce equivalent line capacitance: capacitance which, together with the inductance L, gives the line frequency of oscillation

CZteCZCZtdtdiZte /)/()(



− By definition of Ce

− The period of oscillation is equal to with

and

− It follows that

and

If an additional capacitance is added at the line entrance, the RRRV on the line side is reduced in the same manner as the line frequency of oscillation.

eL LC

f2

1

L

L

dtduu

*2 22*LLL IXu

2LL

IZdtdu

LL X

Zf4

LL

e CCZ

LC 4.044222



− The RRRV on the line side is then

)(22

adde

eL CCL

LCIZ

dtdu

adde

eL CC

CIZ

dtdu

addL

LL CC

CIZdtdu

5.22



Short-Line-FaultInfluence of an Opening Resistor


SLF / Breaking with Opening Resistor

• Some circuit breakers, mainly air-blast, have an opening resistor to assist a short-circuit interruption.

• It was introduced to improve the SLF breaking capability of air-blast circuit breakers, but it has been used also to facilitate the interruption of fast TRVs by some SF6 circuit breakers.


SLF / Breaking with Opening Resistor

• In case of SLF, the RRRV (or du/dt) is modified as follows:

where R = value of opening resistor

Z = line surge impedance

I = short-circuit current

2IRZRZ

dtdi

RZRZ

dtdu


• Very fast RRRV (rate-of-rise of recovery voltage)− Product of fault current derivative by surge impedance− Standard value of surge impedance = 450 Ω

• Triangular waveshape due to travelling waves• Test duties L90 and L75 (+ L60 is some cases)

− Single-phase tests that cover all SLF conditions• SLF performance improved by

− additional capacitor (or opening resistor)

Short-Line--Fault TRV / Summary

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