OPENING OPERATION AND DUTY CYCLE OF POWER CIRCUIT BREAKERS BASIC INFORMATION AND TUTORIALS

How Power Circuit Breaker Operation Works?

Reaction time and speed of modern breakers has increased to reach standard interrupting times of 2 to 5 cycles, with 2 to 3 cycles being common at high voltage. Interrupting time is measured from energizing of the trip coil until the extinguishing of the arc.

The interrupting time during close-open operations may exceed the rated imterrupting time by either 1/2 cycle (for 2 and 3 cycle breakers) or by 1 cycle (for 5 cycle breakers).

The current standard operating duty cycle consists of the following:

Open – T – Close – Open - 3 min – Close – Open

T is defined as either 15 s or 0.3 s depending on whether the circuit breaker is rated for high speed reclosing; this distinction is important in application.

Even circuit breakers rated for high speed reclosing must still be allowed a 0.3-s delay to allow for proper recovery of insulation following the initial fault interruption.

For existing oil and air-magnetic circuit breakers, the standard operating duty cycle was:

Open – 15s – Close - Open.

For additional operations, and/or any close operation in the duty cycle with a time delay of less than 15s after an opening operation, the interrupting rating and related required capabilities of the oil or air magnetic breaker have to be derated.

All operations within a 15-min period are considered part of the same duty cycle and a duty cycle shall have no more than five opening operations.

For guidance on interrupting capability for reclosing service for oil and air-magnetic breakers manufactured after 1960 refer to IEEE C37.0106. Circuit breakers manufactured prior to IEEE C37.7-196010 have different basis of rating.