Substation Transformer Fire

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Thanks. Not sure how that could have happened. If the switchgear fire was on the load side of the transformer, where did the arc come from and why did it last so long? Looks like some sort of relay failure to me, but I wasn't there, so maybe we'll find out. Hope they come clean as to what the cause was. We install transformer protective relaying to prevent that sort of thing.
 
Perhaps the arc was not greatly destructive as do an arcflash and was extinguished by the operation of a ground relay when the arc made a ground contact. Just a thought.
 
Nothing tripped according to the engineer. The arcing stopped when it completely burned through the transformer. They think the fire burned through the control wiring? Apparently, there are four transformers. Two of them are now down and we are being supplied with power by the third operating in manual mode. I am not an electrician so hopefully this makes sense. A week before, another transformer failed, causing the building to experience an overvoltage (530v).

The station is fed from 130kv transmission lines.

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WorkSafe said:
Nothing tripped according to the engineer. The arcing stopped when it completely burned through the transformer. They think the fire burned through the control wiring? Apparently, there are four transformers. Two of them are now down and we are being supplied with power by the third operating in manual mode. I am not an electrician so hopefully this makes sense. A week before, another transformer failed, causing the building to experience an overvoltage (530v).

The station is fed from 130kv transmission lines.

Sent from my HTC One using Tapatalk
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Thanks for the update...but no, it doesn't make sense to me. There should be both overcurrent and differential relays protecting the transformers. Sometimes also a "sudden pressure relay". OC will trip on too much secondary current on the transformer. Diff. trips when a difference is sensed between incoming and outgoing current (corrected for ratio), indicating an internal fault. SP trips on a rapid rise in internal tank pressure, indicating an internal arcing fault. I won't try to second guess the engineers, but two transformer failures seems to indicate that some relay settings or wiring need to be looked at. I was in the substation relay protection end of utility work for over 40 years and I've never seen control wiring damaged due to a transformer fault. But that doesn't mean it can't happen. If the fire in the switchgear burned through the trip wiring, maybe it would prevent tripping of the incoming 130KV breaker. But then, how would a switchgear fire start an arc out at the transformer? And why no burning oil? And what finally tripped to extinguish the arc? Interesting.....
 
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Apparently, the subject transformer did not develop any (arc) fault. Had it, there would be relay tripping. It might be damaged by switch gear arc without involving its internal power wiring.
 
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Here's some pictures. I have no idea what is being pictured here, so please forgive me.
 

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From the pics it looks like the lightning arrester blew, and also the station service transformer connected to one phase burned its primary lead off. If the snake caused all that, then they definitely have some relay issues. All damage appears to be on the load side of the transformers, and that's the part that is relay protected in most substations. Anyway...now that I've shot off my mouth enough, thanks much for the pics. Amazing amount of damage and the arc video shows that it lasted a LONG time. Sure would like to know why nothing tripped. We have suicidal squirrels fairly often, but they always trip SOMETHING. Usually the bus differentials or the ground fault relays. I will have to say, though, that smaller subs probably don't have that level of protection. But even a primary fuse would have saved a bunch of damage and they are kinda no-brainers. Too much current and they blow! No battery, wiring, etc. One noticeable thing is that the station service transformer looks like it was directly connected to the bus, with no cutout (fuse) between. Never a good idea. Could be where all the problems started.
 
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