Testing of cb

PRESENTED BY - GUIDED BY -
AHER SANKET D. PROF. SHAIKH SIR

Why "Testing of Circuit Breaker" is Necessary?
A Circuit Breaker should be capable of carrying, making, and
breaking under normal and abnormal conditions. In any power
system circuit breaker has to withstand power frequency over
voltages and transient over voltages due to switching and lightning.
The performance of a circuit breaker under normal and abnormal
conditions can be verified by performing different type of tests on
circuit breakers. The main purpose of testing of circuit breakers is
to confirm if circuit breaker is able to work on particular voltage
and current ratings or not.
NECESSARY OF TESTING OF CIRCUIT
BREAKER:-

There are mainly two tests classified:
1) Type Test
2) Routine Test
TYPES OF TEST ON CIRCUIT BREAKERS:-

The purpose of type tests is to prove design features and the
quality of circuit breaker. Type tests are not conducted on each
circuit breaker. This is done to prove the capabilities and to
confirm the rated characteristics of the circuit breakers.
1) TYPE TESTS

Routine test is performed before circuit breaker dispatch to
ensure the product. This gives result about defects in materials
and construction of circuit breaker. We can check quality of
material of circuit breaker by performing Routine Test.
2) ROUTINE TESTS:

 Thermal tests
 Dielectric tests
 Measurement of resistance of the main circuits
 Short Circuit tests
TYPE TESTS LISTED BELOW:-

This test determines the maximum normal current that the circuit
breaker can carry without exceeding the maximum allowable
temperature rise In this test the rated normal current of normal
frequency is passed through the current carrying parts of circuit
breaker.
Method are recognized by Indian standards for measuring
temperature rise of parts:-
1) Thermometer method
2) Thermocouple method
3) Self resistance method
THERMAL TESTS(TEMPERATURE RISE TEST):-

1) Breaking Capacity Test:-
Sequence Of Performing This Tests Is As Follows:-
First of all,the master circuit breaker (MB)and the breaker
under test (TB)are closed.
The s.c.current is passed by closing the make switch.
The circuit breaker under test(TB) is opened to interrupt the
s.c.current at desired moment.
SHORT CIRCUIT TESTS:-

2) Making Capacity Test:-
Sequence Of Performing This Test :-
First of all,the master circuit breaker (MB)and the make
switch(MS) are closed.
Then,the short circuit current is initiated by closing the test
breaker (TB).
The rated short circuit making current i.e.the peak value of the
first major loop of the short circuit current envelope is measured
from the oscillorgram.

3(Short Time Withstand Current Capacity
In this test,the rated short-time withstand current is
applied to the circuit breaker
under test for the specified duration of the time.
The rated short time withstand current is equal to be
rated short circuit breaking current and standarad value
of rated duration of short circuit
current is 1 second or 3 seconds.
The current is measured by taking an oscillograph of the
short circuit current wave.
After the test,there should be no mechanical or insulation
damage and any contact welding.

1(Mechanical Operational test
2(One-Minute power frequency voltage dry
withstand test
3(Measurement of resistance of main circuits
ROUTINE TEST LISTED BELOW:-

 This test should be made before temperature rise
test.The measurement of resistance is made by
measuring dc voltage drop or resistance across the
terminals of each pole of circuit breaker.
 The current during the test shall have any convenient
value between 100 A and the rated current of the
circuit breaker.
 The d.c. resistance of main contact of each pole of a
circuit breaker is of the order of a few tens of micro-
ohms.
MEASUREMENT OF RESISTANCE OF MAIN
CIRCUITS:-

 Operational tests are made to ensure that the circuit breakers
comply with prescribed operating conditions within the
specified voltage and supply pressure limits of their opening
and closing devices.
 During routine test five opening and five closing operations
should carry out at
a. Minimum supply voltage and pressure
b. Maximum supply voltage and pressure
After the test,all parts should be in good condition and should not
undue wear.
 MECHANICAL OPERATIONAL TESTS:-

The preliminary preparations of circuit breaker testing include the
following:
 Connect the equipment.
 Adjust the correct values of resistance and reactors to set the
required magnitude of short circuit.
 Connect and set the transformer to get desired test voltage.
 The contacts on sequence switch are adjusted to get desired
timings.
 Oscillographs are adjusted and calibrated.
CIRCUIT BREAKER TESTING PROCEDURE:-

1) Short Circuit generator:-
It is a specially designed generator having very low leakage
reactance to provide short power for testing c.b. It is driven by 3-
phse induction motor.A flywheel is provided on shaft of generator
to supply kinetic energy during short circuit and helps in spped
regulation.
2)Short Circuit Transformer:-
 It is connected between TB and power source.It is used to allow
for flexibility to test at different voltage levels and also provide
isolation between the power source and test breaker.
It is designed to have low leakage reactance and to withstand
repeated short circuit.
EQUIPMENTS USED IN THE SHORT
CIRCUIT TESTING STATIONS:-

3) MASTER CIRCUIT BREAKER(MB):-
It is used as a back up c.b. to interrupt the short circuit current
in event of c.b.under test(TB) fails to operate.It has higher
capacity than the circuit breaker under test.After every test,it is
also isolates the test circuit breaker(TB) from the supply
source.It is set to operate at a predetermined time after the
initiation of short circuit.
4) Make Switch(MS):-
It is very high speed switch used for initiation of short circuit
test current at desired moment.Recently,SF6 gas make switch
are used in short circuit testing station.

5) Reactors(L):-
It is connected in series.It is used to limit or control the
magnitude of the short circuit or test current to its required
value.
6) Resistors and Capacitors (R and C):-
RV shaping circuit(R and C) is connected across the circuit
breaker under test(TB).This circuit is used to control transient
recovery voltage(TRV).Capacitors are also used for voltage
measurement.
7) Measuring Equipments:-
 For the measurements of voltage,voltage dividers are used
and for cureent measurements shunts or CTs are used in the
short circuit testing stations.

Photo Of Testing Of Circuit Breaker

Testing of cb

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Testing of cb