DUTY CYCLE OF CIRCUIT BREAKER

WHAT IS OPERATING DUTY CYCLE OF CIRCUIT BREAKER? 

Operating duty of circuit breaker terms related to opening, closing sequence of circuit breaker.

We always see a term on circuit breaker rating plate operating duty and it is written as:

OPERATING DUTY:  O-0.3 sec-CO-3 min-CO

O: OPEN

C: CLOSE

Time sequence of operating duty of CB

The above terms relate the opening,closing sequence of circuit breaker.

Operating duty chart of CB

                                             

According to above diagram if fault occur on feeder than the relay connected on circuit breaker operated and at that time master trip relay operated and it trip (open) the breaker.

          And after 0.3 sec we can re-close the CB (circuit breaker):

1.If fault clear than closing of CB is successful.

2.If fault present at feeder CB trips instantly means re-closing of CB is unsuccessful.

This 0.3 sec is the time taken by the CB to recovering mechanism (contact open in chamber,arc extinguishing in chamber).

According to duty cycle after 3 minute we take second try(re-closing of CB),this is the relay reset time and breaker mechanism recover time.

If fault persists than circuit breaker relays operate and trip the circuit breaker instantly and this sequence follow for the smooth operation of circuit breaker and next re-closings done after 3 minutes as shown in diagram.

The knowledge of operating duty cycle of circuit breaker is very necessary.The following advantages of knowledge of operating duty cycle given below:

1.It increase the life period circuit breaker.

2.Reduce the maintenance cost.

3.Reduce any electrical and structure damage of CB.

4.Increases the life period of relay.

Important links:

Accessories at circuit breaker panel?

different term regarding circuit breaker rating?