How to Test Circuit Breakers?: Circuit Breaker Testing Procedure and Different Tests and Sequence Switch

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.




siemens circuit breaker testing procedure and types of circuite breaker tests
siemens circuit breaker testing procedure and types of circuite breaker tests | Source

List of Different types of Tests on Circuit Breakers

There are mainly two tests classified:

1. Type Tests:

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.

2. Routine 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.

Type Tests are listed below:

  • Mechanical endurance tests
  • Thermal tests
  • Dielectric tests
  • Measurement of resistance of the main circuits
  • Short Circuit tests

Dielectric Test includes

  • Power frequency voltage withstand tests
  • Impulse voltage withstand test

Short Circuit Test includes

  • Breaking capacity test
  • making capacity test
  • Duty cycle test
  • short time current withstand test

Routine Test are listed below:

  • Mechanical Operational test
  • One-Minute power frequency voltage dry withstand test
  • Measurement of resistance of main circuits


Circuit Breaker Testing Procedure (how to test a circuit breaker?)

The preliminary preparations of circuit breaker testing include the following:

  1. Connect the equipment.
  2. Adjust the correct values of resistance and reactors to set the required magnitude of short circuit.
  3. Connect and set the transformer to get desired test voltage.
  4. The contacts on sequence switch are adjusted to get desired timings.
  5. Oscillographs are adjusted and calibrated.

The automatic sequence of operations during a breaking capacity test is as follows:

  1. Run the driving motor of the short circuit generator to a certain speed and then it is switched off.
  2. Switch on the impulse excitations.
  3. Close the master circuit breaker.
  4. Switch on the oscillograph.
  5. Close the MAKE SWITCH to pass the short circuit current.
  6. Open the circuit breaker under test to interrupt the short circuit current at desired moment.
  7. Switch ff the exciter circuit of the short circuit generator.
  8. The breaking capacity is determined from the oscillograph.

Thus this was the whole procedure for "Circuit Breaker Testing". This takes in a very short time of the order of 0.2 seconds. Because of very short time this whole procedure follow automatically by "sequence switch".

Sequence Switch: Sequence Switch is drum switch with several pairs of contacts. The drum is rotated by a motor to close and open several circuits according to a certain sequence.

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