Tripping of Incomer Breaker

Hello manirul

The fault which caused the blown 11kV fuse on the load side of the transformer, is reflected magnetically through the transformer, and caused the primary (220kV) breaker to trip.

This is a normal condition, depending on setting of protection/discrimination relays at the installation.

It is possible to alter the settings for those, but be careful, because you do not want to exceed design limits for the installation.

Check the Engineers office and read how the system was set up, before altering and protection/discrimination relay settings.

Such alterations are best left to a Technician or Engineer who has wide experience in Power Distribution Systems, as if an error in the settings is made, damage to persons and equipment may be of major proportions.

Kind Regards....

Hello Spark,

I agree with you if the fault happened within the same transformer which is not our case. I believe that the system has two different transformers the first is 220/33 kV transformer; the second is to step down the 33 kV to 11 kV (i.e. 33/11 kV). The 11 kV side of the later transformer is the faulty one.

The question is whether each transformer has two breakers (one on each side) as per normal configuration/practice or not? If yes, the 33 kV breaker (Incoming breaker) of the 33/11 kV transformer is the one who should trip. Otherwise, a protection coordination study should be carried out to avoid tripping of the upstream breaker (220 kV) for faults at load side (11 kV).

Thanks, yes each Trx having two breaker, the relay setting and coordination done by ETAP, from the curve it shows every thing is correct, now we are checking the whole calculation once again and trying to do real time simulation for these model.

Under normal circumstances for a correctly graded protection system, a downstream fault on the 11kv side of the second transformer should not trip the incomer CB of the 220/33kv transformer. Areas to check are:

1.The integrity of the protection for the HV breaker to the 33/11kv transformer( that is if there is HV o/c protection), it could be that the relays picked up the fault but the breaker failed to trip or the relays never saw anything

2. The integrity of the protectin relay co-ordination for the network in question;

Regards,

Under normal circumstances for a correctly graded protection system, a downstream fault on the 11kv side of the second transformer should not trip the incomer CB of the 220/33kv transformer. Areas to check are:

1.The integrity of the protection for the HV breaker to the 33/11kv transformer( that is if there is HV o/c protection), it could be that the relays picked up the fault but the breaker failed to trip or the relays never saw anything

2. The integrity of the protectin relay co-ordination for the network in question;

Regards,