MV AC SwitchgearRecloser

Closing and tripping sequence of medium voltage auto recloser

In this figure we can see the working of the auto-recloser when a permanent fault occurs. Then autorecloser trips after a time delay as per the setting of the first trip on instantaneous or IDMT(Inverse
Definite Minimum Time).
It remains de-energised for a time as per the setting of the first dead time, DTl. Then it recloses and the supply is restored to the distribution system. If the fault persists, the recloser again trips for second time after a time delay as per the setting of the second trip on instantaneous or
IDMT. It remains de-energised for a time as per the setting of the second dead time, DT2. Then it again recloses the second time and the supply is restored to the distribution system. The sequence is again repeated the third time and on the fourth trip when the fault still persists. The recloser goes into lock indicating that the fault is not a transient one but is of a permanent nature. As per the requirement, the setting in the auto recloser can be done such that lock-out is achieved at the second or third trips also.

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Source
handbook of switchgearBharat Heavy Electricals Limited

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