132kv/33kv Network Fault

The time you mention is just perfect for dense Fog.

Can you please go a little bit deeper into your findings? So far I would say there is an Earth fault!

(The other breaker tripped out of courtesy to the other breakers and should be left alone unless ....)

Is the system running normal? No repeat?

If nothing happens maybe you are alight. But chances are that if there is something wrong you have to investigate a hell lot more than you have told us.

Ever since, it did not trip till today, what we did, we ptrolled incomer line from hydro power station where we get a supply from and feeder line which tripped, but we could not get a thing.

If the problem persists you might have an earth fault. But check out the fog issue.

Is it always tripping in the morning hours?

After considerable thought, the only conclusion available here is that there is a directional earth fault present on the network.

If the transformer breaker tripped could be a 132 KV insulator [of the isolator switch or transformer] failure. As Happy singh said, the dense fog and pollution [may be] would amplify the phenomenon. It seems to me all of protection systems [which are involved] are instantaneous so there is no discrimination [selectivity]. But could be also 2 failures: one at the 132 KV bus and another between transformer and transformer CTs.

It is important to check a bit deep into the problem wiyth settings and timings of the earth fault. Relay mappings with their tripping sequence and if possible isolation and identification of fault. You cant generally assume that it is because of fog and if its si good but. Also check in neighbourhood if trippings happened due to fog elsewhere as well.

Detailed study and analysis can be made.But following informations are required.

Single line diagram

Relays provided

Relay settings details with CT ratios

Sequence of tripping.

Event history from the relays.( fault current etc)

Apparently there are many trippings.This may be due to non coordination of relay settings.

OHL tripping could be due to accumulated dust on the incomer OHL insulators copled with fog causing tracking/earth fault. Trafo earth fault protection operation can happen if the transformer has delta on 33kV and Star on 132kV. What is the transformer vector group!