Differential Protection And Auto Transfer System

The differential protection is only for transformer.Apparently from your posting I could infer there was a short circuit within the trasformer and the medium voltage breaker and the LV breaker tripped.

When ATS switched on the bus only is charged and not the faulty transformer, the transformer will get charged only when lv breaker is closed there is no fault current flow.

Please let us know more info for study and proper solution.

Please note to my explanation. I said about it.

The problem observed when a short circuit occurred in one of two transformer windings. The differential relay operated and only relevant medium voltage circuit breaker tripped. The fault clearing stage was done successfully and related low voltage bus bar was dead. In this case the auto transfer system closed the low voltage coupling circuit breaker, and the short circuit point energized again.

REGARDS

MSJ

I am sorry.

In that case first we have to find out whether Diff. relay picked up,

Then high speed master trip relay for mv breaker and lv breaker has picked up.

If both relays has picked up then examine the trip circuit of the lv breaker.(since this has not tripped).

The control circuit is to be examined.I doubt whether Diff. relay is wired to trip the lv breaker.

Unless I look at the control circuit drawing it will be difficult to come to any conclusion May be you can send the as fitted drawing for review.

I will suggest to give a trip command direct to I/C-2 coil from bus transfer scheme. as a backup.

Please think about trip relay drop off time.

REGARDS

MSJ

Now we are in the age of Fast operating relay, the drop-off time is negligible of modern development in relay protection.