Testing of Circuit Breakers

K N srinivasan

CIRCUIT BREAKERCIRCUIT BREAKERCIRCUIT BREAKERCIRCUIT BREAKER

VITAL LINK IN ELECTRICAL NETWORK

SAFEGAURDS COSTLY ELECTRICAL EUIPMENT

RELIABILITY - CRITICAL IMPORTANCE.

Why Tests

What Standards

RecapC-& L charging50-60 HzSym & assymInrush

Why Oscillations

Technical Terms

* Applied voltage: R.M.S voltage applied immediately before it closes.

* Recovery voltage: RMS voltage that reappears across after final arc extinction.

* Restricting voltage: appearing across the arc gap immediately after the current zero

* Making currentpeak valve of the current in the first major current loop.

* Breaking currentRMS current breaker contacts has to deal with.

TYPE TESTS

Temperature Rise

Dielectric Tests.

Dry Pf W/S

Wet Pf W/S

LI W/S

Partial Discharge

RIV

Pollution

IP

Mech. Operation

EMF & MMFMaster CBMake SwitchOptical fiber T/R

Fault MVA = 3 x VL x ILVL= Line voltage

IL = Line current

Contact separation

- ability to close on to fault at full asymmetry;- to prove that there is no significant change in arc energy (T100%, 30%, 60% & T100%) ;

- to interrupt full fault current with appropriate DC component

five Basic Short Circuit Test Duties at various current levels

Test Duty No. T10 T30 T60 T100s T100a

% of ratedS.C. Current 10% 30% 60% 100% 100%

% D.C. Component

For duties other than T100a

O-3mts-CO-3mt-CO

O-0.3Sec-CO-3Min-CO-CO for auto-reclosing breakers

For duty T100a

O-3mts-O-3mts-O

Making current

SEQUENCE

VOLTAGE WAVEFORMS ASSOCIATED WITH SHORT LINE FAULT

surge impedance Z= L/C in ohms T = 2 / LC = 6.66 sec.

SHORT LINE FAULT

Critical Current Tests

lesser than 10% of the rated S.C. breaking current.

4% to 6% and 2% to 3% of rated S.C. breaking current.

Inductive Current Switching Tests

Small inductive - transformer magnetizing current , shunt reactor or motor switching currents

unloaded transmission line, underground cable or a capacitor bank.

The trapped charge on the capacitance - twice L-G voltage breakers of 72.5kV rating and above and the cable charging breaking current tests for breakers of 24kV and above only. Two test duties - breaking current (100% and 10 to 40 %). For 3 phase tests number of applications are:

TestDuty

Test current as a % ofRated cap. breakingcurrent

1 10 to 402 Not less than 100

Capacitive current Switching Tests

withstand the dynamic and thermal stresses due to short circuits.

1.0 to 3.0 seconds.

The rated peak withstand current is equal to 2.5 times the rated short time withstand current (i.e., equal to rated short circuit making current of the breaker).

Short Time Withstand Current Test

DURING TESTNeither sign of excessive distress nor endanger the operator

copper wire of 0.1 mm diameter and 50 mm long.

AFTER TESTMaking and breaking rated normal current

A VISUAL INSPECTION of contacts

80% P F W / S. NO LOAD OPERATION

close and latch satisfactorily

CRITERIA FOR PERFORMANCE EVALUATION

Test Oscillogram of a failure

Examples

Typical oscillograms indicating a Break operation of Circuit breaker during Short circuit testing.

Examples

Parallel current injection

SYNTHETIC TESTING FACILITYSYNTHETIC TESTING FACILITYSYNTHETIC TESTING FACILITYSYNTHETIC TESTING FACILITY

C1 - 1.44MJ, 18F. 400kV

C2 - 2.8F., 500kV

C3 - 4.0F., 400kV

MECHANICAL OPERATION TESTMECHANICAL OPERATION TESTMECHANICAL OPERATION TESTMECHANICAL OPERATION TEST

CLASS M1

2000 MECHANICAL OPERATIONS

CLASS M2

10000 MECHANICAL OPERATIONS