Functional and operational tests for medium voltage circuit breaker operating mechanism components

Circuit Breaker Operation Test

Close Operation Test – Local/Remote

This test is conducted manually, locally, and remotely. In the manual operation test, the spring is charged manually, and the breaker is closed and opened manually as well. For local operation, control power and AC supply are provided to the spring charging motor, and the circuit breaker is closed using the TNC switch. The function of the closing coil and the operation of the spring charging motor are observed. If remote operation is feasible on-site, it is performed using the remote system; otherwise, a local signal is sent to the remote terminal to observe the breaker's operation.

Trip Operation Test – Local/Remote

The trip operation test is also carried out manually, locally, and remotely. During manual testing, a manually charged breaker is opened using the trip switch. For local operation, control power and AC supply are provided to the spring charging motor, and the circuit breaker is opened using the TNC switch, with emphasis on observing the function of the tripping coil. Remote operation depends on site readiness; if ready, it is executed via the remote system. If not, a local signal is sent to the remote terminal to observe the breaker’s operational behavior.

Protection Trip Test

For this test, the breaker must initially be in the closed position. Auxiliary rated voltage is then supplied to the master trip relay to observe the opening of the breaker and the position of the trip coil.

Functional Test for Medium Voltage Circuit Breaker Operating Mechanism

Photo 1 shows a medium voltage vacuum circuit breaker wiring diagram schematic:

Emergency Trip Test

In this test, the breaker must be in the charged or ON position. By pressing the emergency push button, we trigger the trip and observe the operation of the circuit breaker opening.

Auxiliary Switch Operation Test

With the breaker in the open position, use a continuity tester to check the auxiliary contacts (NO/NC status). Then close the circuit breaker and recheck the same contact with the continuity tester to confirm that its status has correctly changed to NC/NO.

On-Off Indications (Lamp + Flag)

When the breaker is open, check the lamp and flag indicators of the relay. Close the circuit breaker and check the operation of the same indicator lamp again.

Trip / Trip Circuit Healthy Lamp Indication

Operate the relay and observe the indication of the trip lamp.

Limit Switch for Spring Charge Motor

In this test, AC power is supplied to the spring charging motor, and we observe the motor operation and spring charging process. Once the spring is fully charged, the motor operation should automatically stop.

Test / Service Limit Switch

This test verifies the operation of the test/service limit switch. During the racking out of the breaker, observe the indicator switching to the test position; during the racking in of the breaker, observe the indicator switching to the service position.

Operation Counter

If an operational counter is provided in the breaker, this test is conducted. Operate the breaker and check for changes in the counter to record the number of operations.

Heater / Heater Switch / Thermostat

Supply control AC power to the heater and check if the heater operates properly.

Function of Illumination & Socket Switch

In this test, focus on the operation of the panel internal illumination and socket switch. Manually operate the limit switch and observe the operation of the illumination circuit.

These testing procedures are essential for comprehensively evaluating all functions of medium voltage circuit breaker operating mechanisms, ensuring the safety and reliability of the equipment.