Lightning strike analysis on a delta/wye system 1

[Xr70rider23]

I am doing analysis on a outage assumed to be caused by lightning. After doing a lightning study, it is believed that several lightning strikes hit the 13kV line down stream of an oil recloser. The fault happened to clear only a single high side fuse of a delta/wye transformer. A collogue is persistent that in a delta/wye system, if there is a fault on the low side of the transformer, 2 fuses should have blown.

I do not think this is the case... My question is, should multiple fuses have blown?

 

[davidbeach]

No, you’ll get one fuse blown and one almost blown fuse. The two fault currents won’t be exactly the same, load and all that, and the fuses won’t have identical melt times. But you should replace both so you don’t have to go out the week or next month to replace the second one after a minor overload.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Xr70rider23]

Thank you for the reply davidbeach! I agree with you. Having multiple fuses blown would not be concerning but it also is not uncommon to only blow one

 

[davidbeach]

Also not uncommon to only blow two fuses blown for a three phase fault. But don’t trust that third fuse.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[cranky108]

I saw that many years ago. The problem is when they were required to replace three fuses, they did not know what to do with the unblown fuses. I fount that the service men would return them to the warehouse. And the warehousemen would return them to stock.
No wonder we had so many unknown events. Old fuses that were prewarn, would blow for what seemed to be no reason.
The problem was when the servicemen was required in the manual to replace all three fuses, it was never specified he was suppose to throw the unblown fuses away.
That was fixed, wrongly, in that the warehousemen, were instructed to not take the fuses back.
I suppose the servicemen might just keep them on their trucks.

 

[Xr70rider23]

Interesting cranky108!

I know standard practice is to throw them away… but I never really thought to make sure that’s what they were doing. I’ll follow up with them and make sure the old ones get thrown away. Thank you for the tip