IEEE Tutorial on Design and Application of High-Voltage Circuit Breakers July 2008 1

High-Power Testing ofCircuit Breakers

Prof. Dr. Rene Smeets

KEMA T&D Testing

The Netherlandsrene.smeets@kema.com

IEEE Tutorial on Design and Application of High-Voltage Circuit Breakers July 2008 2

categories of tests

development teststype-tests (for certification)acceptance tests

IEEE Tutorial on Design and Application of High-Voltage Circuit Breakers July 2008 3

1 development tests

ordered by: manufacturer

standard: according clients instructionslaboratory: mostly at manufacturer's site

product development

testing of prototypes

IEEE Tutorial on Design and Application of High-Voltage Circuit Breakers July 2008 4

2 type tests

provide confidence that a duly indentifiedproduct conforms with requirements of a specific standard

ordered by: manufacturer

standard: (Inter)national standard

aim: certification

laboratory: independent testing instituterecognised group of manuf. labs

IEEE Tutorial on Design and Application of High-Voltage Circuit Breakers July 2008 5

3 acceptance tests

ordered by: user of the equipmentstandard: agreement manufacturer - user

laboratory: independent testing institute

recognised group of manuf. labs

verify that a certain product complies with a specific application specified by the user

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test methods

direct testing- on the grid- generator fed- capacitor bank fed

synthetic testing

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direct testing

pros

simple

cheap

representative

high-power available

cons

poor flexibility

difficult to adjust

laboratory supplied by power grid

EDF

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pros

adjustable

flexible

no influence on local grid

con

huge investment

generator supplied laboratory

direct testing

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generator master breaker

current limiting coils

TRV generating circuit

voltage measurement

current measurement

test objecttransformersmaking switch

slamecka 1966

direct test lay-out

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increase of capacity per break

electra 2003

highest lab-power

available

GVA / break

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synthetic testing

example: short-circuit test of a CB (three-phase)420 kV - 63 kA - 50 Hz

⇒ necessary power: 420 x 63 x √3 = 45830 MVA

this exceeds any laboratory's direct power (Max: 8400 MVA)other methods must be sought:

- single phase test: necessary power 45830/3 = 15277 MVA- half-pole testing (if possible): 15277/2 = 7638 MVAthis still does not match the power-voltage characteristics of the most powerful labs.

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solution

short-circuit current

reignition

interruption

contact separation

arcing time

transient recovery voltage

after interruption there is only the need for a sufficiently high voltage- from precharged capacitor

special circuit needed to reignite the arc

⇒ synthetic test

before interruption a sufficiently large power must be available to maintain the full (arc) current at moderate voltage (< 60 kV)- from generators

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generator circuit capacitor circuitaux

TO

Lv

G

Ug

Ig

Ig

Ug

Ii

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UTRV

ChUTRV

Ls G

IiR

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+-Uh0

TO

synthetic tests

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synthetic testing

Synthetic circuit (parallel current injection)

Ig+Ii

UiUTRV

Ch

Ls G

IiR

C

+-

auxLv

G

Ug

Ig

TO

UTRV

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current through test-CB

delayed current zeroinjected

current

generator current

synthetic testing

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three-phase synthetic testing

first pole to clear

last poleto clear

last poleto clear

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synthetic testing in practice

2 x cap. bank720 kV - 1.7 MJ

test methods:current injectionvoltage injection

ratings to be tested synthetically:1100 kV - 63 kA - 60 Hz - 1Ø (experimentally)550 kV - 63 kA - 60 Hz - 1Ø (routine)245 kV - 63 kA - 60 Hz - 3Ø

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high-power test of 1100 kV CB

test-breaker

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switchyard (245 kV)

generator building

(8400 MVA)

on-board trans-former testing

new MV test lab (38 kV)

synthetic installation (720 kV)high-power labsopen-air test site

test station lay-out

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grey zones in testing

Test-circuit should represent the service conditions of equipment as much as possibleStandards prescribe inherent behaviour of test-circuits.Inherent means 'naked' circuit only, without test-object.This can be different when a real test-objects interacts with the test-circuitThen, the representation must still be realistic.

But: test are possible with test-circuits that show inherently adequate behaviour in accordance with standards, but do not reflect realistic service conditions

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circuit breaker testing

Many arcs in series: high total arc voltage counteracts source voltage (in 800 kV testing: 8 arcs in series)Especially with- synthetic testing (auxiliary breakers)- when testing breakers with multiple arcing chambersCurrent supply sources must have terminal voltage as high as possible to guarantee sufficient arcing stressesRisk is to apply too little energy into the fault current arc. Testing is too light in that case

IEEE Tutorial on Design and Application of High-Voltage Circuit Breakers July 2008 225 10 15 20 25 30 35 40 45 50

ampl

itude

time [ms ]

arc energy with14 kV s ource

arc energy in s ervice s ituation

current in s ynthetic tes t

arc voltage

current in service s ituation

influence of manyseries arcs on current

Source voltagetoo low

Source voltagehigh enough

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Immediately after interruption

Immediately after interruption hot gases are still in the gap and feel fast rising voltage:thermal stresses

A little later very high voltage is reached across the open gap:dielectric stresses

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transient recovery voltage (TRV)Voltage immediately after current interruption (TRV) is of crucial importance for success or failure

circuit breaker arc strongly interacts with TRV circuittest-circuit topology very importantmicrosecond scale

time (us )

current,voltage

time 5 us /divvoltage 5 kV/divcurrent 50 A/div

terminal fault TRV

s hort-line fault TRV

s hort-line fault currentterminal fault current

interaction interval

current zero

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high-frequency effects of circuits

Seldomly specified in standardsWill affect result of tests in which high-frequency behaviour is important

Example: interruption tests with vacuum circuit breakerSuch a breaker is very good in interruption of current of high-frequency

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effect of TRV circuit

0.0

0.4

0.8

1.2

1.6

2.0

0 50 100 150 200

-50

50

150

250

-5 0 5 10 15 20 25 30

series damped + pow er freq.

parallel damped + power freq.

series damped TRV

parallel damped TRV

current at re-ignition (A)

TRV (pu)

re-ignition

time (us)

time (us)

Research:cable systems have oscillatory TRV, so

test should be performed with oscillatory TRV

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half-pole tests for (U)HVtest voltage application across full-polehalf-pole testingquarter-pole testing

non-full pole ("unit"-) testing should consider uneven voltage

distribution across circuit breaker,

especially when there are no grading capacitors

full-pole testing eliminates doubts

800 kV breaker

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half-pole testing of GIS

2U

2 U

2U

hot exhaust gas from breaker

Full-pole test:interrupter stress OK

internal stress OK

Half-pole test:interrupter stress OKinternal stress NOK

2 U

U

2 U

U

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ultra high voltage testing

For metal enclosed breakers, half-pole testing does not represent the conditions in service:

dielectric stresses of half-pole tests equivalent to full-pole conditions- between phases- between phases and enclosureeffects of exhaust gases equivalent

mechanical stresses equivalent

forces (electrodynamical stresses) equivalent

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single phase testing of three-phase circuit breaker

Often practiced when power of test laboratory is insufficientIn principle possible, but with care

Not realistic when common mechanism is controlling contact movement (circuit breaker, earthing switch)Beware of three-phase interactions, that single phase circuits fail to represent

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three-phase testingof three-phase devices

current

recovery voltage

no-load contact movement

three-phas e tes t contact movement

s ingle-phas e tes t contact movement

contact s eparation

voltage: 80 kV/divcurrent: 111kA/divtime: 10 ms /div

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conclusions

Standards do not cover everythingGrey zone exists between allowable but different stresses that make life easier/worse for a breakerTest-engineers knowledge and test-lab policies must ensure that realistic testing will prevail:- supply sufficient arc energy even for highest

voltages- have knowledge of arc-circuit interactions- being aware of high-frequency pitfalls- test three-phase when necessary