Causes of Tripping?

Tripping may be caused by over loading due to damage to A to C feeder. Get that fixed.

Tripping may be caused by overindulging in alcohol, too.

Hire a competent electrician to evaluate it and fix it. If you have to ask, you can't fix it.

132kv will turn you into a crispy critter very quickly.

One way or the other, Lyn, you're close to the root cause here. Hopefully, the actual problem is that this student has already overindulged in alcohol and is now tripping over this homework assignment given during a school break. There is also the disturbing possibility that a power utility has hired people to design their network that know nothing about power grids.

I have to agree with both you and Lyn. And this does sound like hypothetical home work scenario I often wonder about these AP posts

In order to know the cause of tripping, first you must check the protection which operated, i.e earth fault relay, overcurrent, differential etc and then start from there. The damage caused by external source is not detailed and I can only assume that there may have been a damage due to excavation, in which case the earth fault relay has operated on both feeders. It would be normal for the feeder from substation A to trip as the fault was direct. The tripping of feeder from substation B is not evident but it can happen, especially if the transformer neutral is connected to earth through an impedance. The problem can be avoided but one must have the full details of the distribution network to work it out.

THANX FOR UR REPLY ,

Can you confirm if the earth fault relay has operated on both feeders, and can you give details of transformers connected on both feeders.