Arrester Problem

Yesterday one of our younger linemen had problems on a small radial section on our rural area.
The initial call they found a blown fuse on the tap and a blown arrester on an irrigation bank approximately a mile and a half away. They replace the arrester and refused.
When they closed the fuse it blew and took out another arrester about a quarter mile closer on another irrigation bank.
Again they changed the arrester, refused and the fuse blew along with another arrester about another half mile closer.
They repeated the same process but this time the fuse held.
All the arresters were 9 kv ohio brass polys. The whole radial line is 3 miles long.
Any ideas? I haven't had this happen before. Thanks

I would say it is ferroresanance, most likely to occur on a radial feed with 3 phase delta connected primary side transformers. The only solution is to have a GOAB switch that will close all 3 phases at a given time.
Otherwise you need some load somewhere to pick up the back feed.
It is very ugly stuff, an engineer can't even explain it from the ones I have been around.
The reason for arrestor failure is they say the voltage may be 2 times the normal voltage.
Also you may never see it again for many years

Thanks! I had given it a thought but I didn't know the back feed could be that high. Whenever I have come across it, it was on underground and on primary going out into the middle of a field with a transcloser that fed a well.

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Originally Posted by Divemaster

Thanks! I had given it a thought but I didn't know the back feed could be that high. Whenever I have come across it, it was on underground and on primary going out into the middle of a field with a transcloser that fed a well.

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Voltage 25kv?

If you have a floating neutral on that Delta bank hang a 4th cutout with a solid blade tap the top side of the cutout to the pole ground and the bottom side to the floating neutral close the solid blade then close your bank in and or lateral then open the solid blade un-grounding the floating neutral, hang solid blade down by the neutral and it should be a clue for the next man coming behind you and it should solve your problem with the blowing arrestors.

It would be nice to know the primary voltage, but I am guessing with 9 kv arrestors the primary was around 12kv. Also what kind of secondary load, wye or delta. I have no experience with delta banks being fed over 8 kv, and thought ferro was with the higher voltages, but LNF could be onto something.

Lewy, it used to seem that it only happened on higher distribution voltages or where longer runs of URD fed overhead but it started happening a good bit on our 12kv feeders especially closed Delta banks, that's the reason a few of us started hanging the 4th cutout, so far it has worked every time group operated switches seem to work really well also they just aren't always practical, ferroresonance is a funny thing.

If they were floating wye power and lighting and no load you can over voltage and blow arrs. Need to tie floating N down or need load or KPF like was stated

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Originally Posted by trigger

If they were floating wye power and lighting and no load you can over voltage and blow arrs. Need to tie floating N down or need load or KPF like was stated

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This only happens on a fused line,like it was stated the arresters are not rated for the over voltage that occurs because of the delta bank.Like it was stated tie it down or remove all the arresters until the line is hot then tap them on which is a lot of work.The best solution is to have 18kva arresters on all fused lines with delta banks on them then the problem goes away,your not exceeding the line to line voltage of your arresters.When you close that fuse you have an instantanious line to line voltage until the delta colapses.

That happened to me one time at a port facility. I had a tap burning on a 140K fuse, 3-ph. When the tap burned off, I heard loud pops. It was the bottom of the MOV arresters blowing out on the phase where the tap burned off. Since I was a new Troubleman I didn't know what to think. An older Tman showed up to help and he explained the 3-ph was all Delta. Apparently the Line gang installed all 9kv arrestors when they did some upgrades. They were originally 18 KV arrestors.