Generator Circuit Breaker

Verification of time quantities in commissioning test for Generator circuit breaker (GCB) according to IEC/IEEE

After a Generator circuit breaker has been installed commissioning tests shall be performed.

The purpose of commissioning tests is for confirmation of:

  • absence of damage, due to transport and storage
  • compatibility of separate units
  • correct assembly
  • correct performance of the assembled generator circuit breaker

Verification of generator circuit breaker time quantities:

The following time quantities shall be verified in commissioning tests:

1.Closing and opening times, time spread

These measurements shall be made at max pressure and at the supply voltage of the auxiliary and control circuits, measured at the terminals of the equipment and under typical load conditions of the supply voltage source:

    • closing time of each pole, the time spread of the poles and when possible time spread of the breaking units or groups of units of each pole
    • opening time of each pole, time spread of the poles and when possible time spread of the breaking units or groups of units of each pole.

These measurements shall be carried out for separate opening and closing operations and for the opening and closing operations of a CO operating cycle.

In the case of multiple trip coils, all shall be tested and the times recorded for each.
The supply voltage before and during the operations should be recorded. Furthermore the instant at which the three-pole control relay, if any, is energised should also be recorded to enable calculation of the total time in three-pole operation (relay time plus closing or opening time).
When the circuit-breaker is provided with resistor closing or opening units, the resistor insertion times should be recorded.

2.Operation of control and auxiliary contacts:
The timing of the operation of one of each kind (make and break) of control and auxiliary contacts should be determined in relation to the operation of the main contacts, on closing and opening of the generator circuit breaker.

3.Recharging time of the operating mechanism:
The following recharging time shall be verified as applicable:
a) Fluid-operated mechanism:
The operation time of the pumping device (pump, compressor, control valve, etc.) should
be measured:
–  between minimum and maximum pressure (cut-in and cut-off of the pumping device);
– during the following operations or operating sequence, starting each time with
minimum pressure (cut-in of the pumping device):
– closing three pole.

– opening three pole.
– CO three-pole.
b) Spring-operated mechanism:
The recharging time of the motor after a closing operation should be measured at the site
supply voltage.


IEC/IEEE 62271-37-013

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