What is the Duty Cycle/Operating Sequence of Circuit Breaker specified on the Name Plate

[We keep wondering what the heck this sequence on the name plate of the Circuit Breakaer. Lets find it out now.

What is the Duty Cycle/ Operating Sequence of CB?

It is the Mechanical Duty requirement to be fulfilled by the  Operating Mechanism of the Breaker and specified on the Name Plate of the Breaker by the Manufacturer.

What is its Significance ?

It is mainly used during Circuit Breaker Auto Reclosing.

How is it specified ?

It specified as: O-t-CO-t’-CO and generally given as  O-0.3 SEC-CO-3 MIN-CO, where O is CB Tripping, t is the Dead Time, CO is Reclose with immediate Tripping (AR Unsuccessful)  and t’ is the Reclaim Time and then the cycle continuous, if its a Multishot AR or the Fault reoccurs.

Sequence of Operation:

1. When there is a fault, the concerned relay operates, which inturn operates the Master Trip Relay (86).
2. CB Trip initiates and at the same time Auto Reclose Initiates.
3. CB Trips in about 30ms, which is indicated by “O” in the Duty Cycle.
4. Then CB will remain open for some time (0.3 sec) to complete the Arc Quenching which is called as Dead Time and is indicated by “0.3Sec” in the Duty Cycle.
5. After 0.3 sec, if AR is in Service, a Reclose will be attempted, and if the fault persists, CB Trips immediately  ( AR Unsuccessful ) which is indicated by “CO” in the duty cycle.
6. If its a Single Shot Auto-reclose, the Breaker will go into Auto Reclose Lockout, that means , the AutoReclose Relay will not give any further Reclose Command to the Breaker.
7. After CO, there is a Reclaim Time of 3 Minutes, in which the CB gets ready for Closing, which includes CB Spring Charging Time, indicated by “3 Min” in the Duty Cycle.
8. After the Reclaim Time has completed, Second Reclose will be attempted in following two cases:

Case i) If its a Multishot AR, the breaker will close again, and if the fault is cleared it will remain close, but if the fault is still                         there then the breaker will open immediately, and now breaker will remain open until it is closed manually.

Case ii) Auto-reclose was successful (Fault Cleared & Breaker had closed), but after the Reclaim Time, the Fault Reoccurred.                       In this Case, the Duty Cycle will continue.

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