Primary Faults

Had a nice learning experience today. Went to help on a URD fault. Going on fault indicators we isolated and closed back in at terminal pole and got good majority of the customers on. Okay, like I said fault is isolated based on fault indicator, go to normal open close in and find that we ended up blowing another fuse from the other direction.

Like I said the stretch of cable was isolated based on fault indicators.

Go and hi-pot the cable with the EZ-Restore and shows good. Alright fluke thing, refuse and blows back again.

Get extra help with the von-thumper. Same thing radar/hi-pot cable with it, shows good....

Long story short it ended up taking a stair-stepping method of closing in the the cable to find out what was causing it to blow--Midevil style. Our equipment was testing good but would blow back.

Problem; the URD cable burning into itself. Ya'll ever see anything like this?

Remember it also went through 1 fault indicator that didn't indicate anything...guess there wasn't enough fault current at the time to indicate a fault when it did fault due to a combination of things including soil conditions. Hell maybe the fault indicator didn't work.

Yes, squirrels chewing at the cable. They chewed a pin hole that would hi-pot but not hold load. It was under the guard. The guy I worked with, good cableman, balled up a small piece of Self Amalgamating Tape and shoved it into the hole with a small screw driver. More SAP tape and finally a few wraps around the "temp repair". It held when energized. It was reported as "FIX NEXT DAY!!!" A year later I was called to the same location and the cable was Blown and had to be replaced that night. Seems the "FIX NEXT DAY!!!" was ignored but did hold a whole year.

Seen that happen before, frustrating as hell.

If I remember correctly the second time was good for 10 or so hours of OT.

I've had a cable fault where we looked for the fault, transformer to transformer with a high potter.

We got to one section, tested, and energized. Went to the next pot, no power! Checked the maps, scratched our heads, and ended up isolating that piece and energizing the rest of the loop from the other feed.

We found out the cable had faulted, the conductor burned in two and the insulation melted back over the end of the conductor. So when we energized, it just set there hot to the end of the conductor that had burned in two.
It ended up being 25 kv cable on our 15kv system, 220 mil. Too much insolation I guess! It was a nightmare to find though!

rcdallas™ wrote:Problem; the URD cable burning into itself. Ya'll ever see anything like this?

Went on bad primary underground call this morning. Wire tested good when we would hi-pot, but blew the fuse when it was thrown in. We ended up finding the fault under the consumer's concrete driveway.

What do you mean when you say the cable burned into itself? Our cable had a decent size hole blow out the side where the fault happened. I am having a hard time figuring out why the cable would test good when it was not.

I'm glad I'm not the only one who gets to share some of this underground pie

By burning into itself imagine a chunk of conductor missing inside the insulation of the cable.

I've seen heavy insulated O/H Aluminum wire, like Hendrix cable, corrode 4 or 5" of conductor at a small hole in the insulation. Aluminum oxide is an insulator. Try find that puppy. I used a Modiwark on a stick and moved it down the "wire" until it no longer showed energized. Blew my mind the first time to be sure.

Same can happen on U/G.

CanadianLineman wrote:I've seen heavy insulated O/H Aluminum wire, like Hendrix cable, corrode 4 or 5" of conductor at a small hole in the insulation. Aluminum oxide is an insulator. Try find that puppy. I used a Modiwark on a stick and moved it down the "wire" until it no longer showed energized. Blew my mind the first time to be sure.

Same can happen on U/G.

Are you calling a modiwark a tic-tracer? (voltage detector)