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 Test2) 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 pressureb. Maximum supply voltage and pressureAfter 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