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Old 07-15-2020, 11:24 AM   #21
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Last job I did used Eaton contactors in the MCC buckets. The contactor monitors voltage, phase loss, on off condition. They trip out in the event of those conditions to protect the load.
I worked for an Eaton/Cutler-Hammer distributor. We had great success with their contactors per MCC applications. Biggest job was a tier 2 plant that fed Nissan.
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Old 07-15-2020, 11:33 AM   #22
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I worked at a water utility out west. As electricians, we were scheduled with PM's for all electrical equipment. Maintenance engineering developed the schedules. It actually worked out well. We did IR surveys twice a year. Any suspicious reading and the station was taken down and the condition was checked/corrected. We caught several loose connections that would have resulted in failures eventually, mostly on the 5kv gear and transformers. We also used an ultrasonic probe (microphone) to pick up arcing. We got several hits using that on the 480 gear; saved us a lot of failures.
Please tell me you are using a parabolic mic and not a probe.

We had to unlock the 25kv transformers for a engineer to do ultra sonic testing.
Engineer puts on full flash then pulls out a ultra sonic wand. I told him he didn't need PPE as we was not going to allow him to carry on. He went on a rant then finally asked me why.

I told him you have a wand connected with a cable to a box on your side which is then connected to headphones. If there is a leak from the cable its going to jump to the wand then to the head phones and blow your head off.
Poor guy stood there for a minute white as a sheet. Turns out this wasn't the first high voltage transformer he had tested by holding the wand next to the cables.
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Old 07-15-2020, 11:50 AM   #23
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I had a engineer wipe off the dust on a 4160 volt cable to read the type number once. We had just shut it down and he did not wait for us to discharge the cable to ground, and put on clamps.
He discharged the capacitance charge quick. Bet he never did that again.
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Old 07-15-2020, 11:59 AM   #24
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Originally Posted by gpop View Post
Please tell me you are using a parabolic mic and not a probe.

We had to unlock the 25kv transformers for a engineer to do ultra sonic testing.
Engineer puts on full flash then pulls out a ultra sonic wand. I told him he didn't need PPE as we was not going to allow him to carry on. He went on a rant then finally asked me why.

I told him you have a wand connected with a cable to a box on your side which is then connected to headphones. If there is a leak from the cable its going to jump to the wand then to the head phones and blow your head off.
Poor guy stood there for a minute white as a sheet. Turns out this wasn't the first high voltage transformer he had tested by holding the wand next to the cables.
Yes, it was a parabolic mic. I was kind of remembering that our planner had always said "ultrasonic probe" on the work orders.
That was last decade, and PPE and arc flash stuff was just getting serious. We had flash suits, but we would remove 5kv transformer covers all the time, same with the 12.4 to 480 or 5kv and shoot the connections. We had non-contact testers that could be used on a hot stick, plus a contact meter that would go to 25kv if we absolutely needed it.
On some of our old GE disconnects, a blade would not disengage from the contacts (prongs). Had to be careful with those, thus the testers.
We also did all the splices on the 5kv submersible wells. After sitting all winter, I got a good idea why that little sticker of that very angry electricity god on the front of the enclosure looked like that. We had several "pooms!" when we called ops for a start. Pretty cool stuff.
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Old 07-15-2020, 12:08 PM   #25
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I had a engineer wipe off the dust on a 4160 volt cable to read the type number once. We had just shut it down and he did not wait for us to discharge the cable to ground, and put on clamps.
He discharged the capacitance charge quick. Bet he never did that again.
When I was in the IBEW out west, my foreman walked by a 5kv cable with a bare end lying at about mid-calf level. An electrician on the other end was Hi-potting it. He drew an arc and it burned a hole through his jeans, into his calf and out his heel through his boot. Customer spec on Hi-potting was 3 times line voltage. Nice little 15kv zap.
He had gone under the red tape without asking. Hmm.
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Old 07-16-2020, 12:11 AM   #26
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I was troubleshooting some 5kV soft starters once that kept shorting out the SCRs. We could hear a ticking sound through the closed door, like something arcing to ground inside. But when we killed power and opened it, we couldn't find anything. So we opened the door, set up a high speed video camera, turned off the lights, then energized it while standing about 15 feet back. What we saw and recorded was an eerie spider web like phenomenon, crawling across the surface of the conductors used inside. It looked like is was alive, searching for something. Then eventually it crawled across all of the cables and found a point close enough to a bolt head to make the jump, and that was the ticking sound we heard. Turned out that the factory had over tightened some straps and compressed the rubber insulation too much, causing corona discharge. then they had also forgotten to wipe down the cables after installing them, so they were covered with a thin film of dust that was conductive enough to allow tracking of the corona until it found a ground point.



I wish I had a copy of that video, but the guy who owned the camera quit right after that.
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Old 07-16-2020, 07:01 AM   #27
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Had a 4160 enclosure explode with so much force we never found the door. When we cut open the terminations the contractor never removed the semicon and it took two weeks to fail.

Lots of “3 year” terminations. That’s where someone cuts everythjng back but no termination.

Saw one in Georgia where the guy changing out 5 kV MV-105 didn’t know how to do it. So he cut the jacket, shield, insulation off very straight and flat then butted it up tight so the shield was loosely against the mechanical lug. After six months it had eaten about 18” of cable on both ends without failing catastrophically yet.

Recently saw a “home made” splice. Everything was mostly cut back. They wrapped a piece of #8 loosely around the shield. Then wrapped everything in 130C. Then a layer of some off brand silicone tape (70). Then put on two heavy wall adhesive heat shrink jackets, one over the other, then vinyl tape over everythjng for good measure. No stress relief.

I understand medium voltage can do strange things but every “strange” situation I’ve ever seen comes down to the same simple issues. The same guys that screw it up are the same ones that try hydraulic repairs with a rag and hose clamps. MV is the point where you have to use high electron pressure practices.
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Old 07-24-2020, 07:06 PM   #28
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We do yearly IR scans of all our MCCS. We’ve identified loose clips this way. We also regularaly vacuum our MCCs because of combustible dust rules. We often find things needing repair during our routine cleaning.
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