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upstatelineman
01-22-2009, 08:40 AM
We have a phase grounded somewhere on one of our feeders. I've run into
this before but, had to keep taking outages to isolate the section and
then lift individual transformer taps to find the problem. Which in this case was internal of an old cow face.

I was wondering if anyone has had this trouble on there Delta system and
is there equipment to isolate the source without outages or at least so many.

topgroove
01-22-2009, 10:24 AM
been through this many times. sounds like you have a transformer or even a bad lightning arrestor going bad somewhere. the only way to narrow it down without an outage is to tie the feeder with a different substation and than break parralell at a different spot to see if the ground goes away at the original station. with a couple crews in the field leapfrogging eachother and some station electricians at the substations you can probebly narrow it down to a small section of the feeder in one day.

Avid
02-01-2009, 02:54 PM
pardon the ignorance...

How do you know that one phase is grounded on a delta system? I've heard that you can actually have a ground on one of the phases without reaction - but that two grounds would cause it to start burning, etc.

We have a lot of 4800 delta here, and our company isn't the best at training. I realize a lot of training comes over time and experience, but we had a guy get killed early last year because of delta backfeed (a single phase laid energized on the ground, not burning).

wtdoor67
02-02-2009, 08:40 AM
If you have a good ground on a phase of a Delta it would give you a zero reading from that phase to a ground. Simple. The other 2 ungrounded phases will give you your nominal voltage when checked with a voltmeter to ground. Once the grounded phase is identified then you can only sectionalize until you discover the source of the ground on the phase.

If you have ever messed with ungrounded delta banks such as a 480 bank, then do a little experimenting. You can of course ground one leg of such a bank, termed a "corner ground". Then it will behave just as your 4800 Delta, except at a lower voltage. You would read, nominally of course. 480, 480 and 480, in the phase to phase checks. To ground you would read 480, 480 and zero. The zero reading would represent the grounded phase. Savvy?

Boomer gone soft
02-03-2009, 09:25 PM
pardon the ignorance...

How do you know that one phase is grounded on a delta system? I've heard that you can actually have a ground on one of the phases without reaction - but that two grounds would cause it to start burning, etc.

We have a lot of 4800 delta here, and our company isn't the best at training. I realize a lot of training comes over time and experience, but we had a guy get killed early last year because of delta backfeed (a single phase laid energized on the ground, not burning).

If it was truly a single phase, then it most likely was not delta. The "backfeed" you are referring to could have been from a bank possibly.

All of that is not the point. Any phase, delta or wye, can lay on the ground hot if it is not drawing enough amps to open a door or if a recloser is malfunctioning.

BTW, grounding two phases of delta is a dead short. It's the same as tying those two phases together and using the earth as the "connector". Savvy? (as door says):D

Avid
02-04-2009, 12:37 PM
If you have a good ground on a phase of a Delta it would give you a zero reading from that phase to a ground. Simple. The other 2 ungrounded phases will give you your nominal voltage when checked with a voltmeter to ground. Once the grounded phase is identified then you can only sectionalize until you discover the source of the ground on the phase.

If you have ever messed with ungrounded delta banks such as a 480 bank, then do a little experimenting. You can of course ground one leg of such a bank, termed a "corner ground". Then it will behave just as your 4800 Delta, except at a lower voltage. You would read, nominally of course. 480, 480 and 480, in the phase to phase checks. To ground you would read 480, 480 and zero. The zero reading would represent the grounded phase. Savvy?

Thanks for the info on the 480 bank. That's pretty cool

I understand about testing phase to ground to determine which phase does have the ground on it. But go before that step. How was it determined there was a ground on the line to begin with? What symtoms are there? Or is that something the RDO tells you?

We did have a ground on a 3 phase 34.5/wye line. They did just what you said and all phases read zero. Engineering said it was because the span distance was so long and even with them being open were appearing grounded. 10 miles I think radial feed. That's over my head though.

Boomer- yeah we had a 2nd fatalaty with a single phase wye line. Either fused so high or never made a good ground to blow the fuse. The one I mentioned was delta. Service man left the solid in at the regulator and opened the cutout. It backfed down the line :(

Two too many...

wtdoor67
02-04-2009, 02:27 PM
I understand about testing phase to ground to determine which phase does have the ground on it. But go before that step. How was it determined there was a ground on the line to begin with? What symtoms are there? Or is that something the RDO tells you?~~~~~~~~~~~~~~~~~~~~`````````


Comeon man. Ask your Jman or Foreman. Maybe some kind of sub indicator, maybe someone, for whatever reason, put a voltmeter on the primary and said. Hey Joe, this phase doesn't read anything to ground. What's the deal? Joe. Hell it's probably got a ground somewhere, see if the other 2 read anything. Yeah, they read about 4800 volts. Joe. Yep, got a ground somewhere. Maybe it has ground relays in the sub with indicators. I've never been in a very sophfisticated Delta sub.

climbsomemore
02-04-2009, 02:32 PM
back when Delta was all the rage stations would have a lamps that would light if the associated phase picked up a ground.

Trees in the line are enough to ground a delta phase also

Avid
02-04-2009, 04:19 PM
back when Delta was all the rage stations would have a lamps that would light if the associated phase picked up a ground.

Trees in the line are enough to ground a delta phase also

Thanks, that's pretty cool. The subs out here are different than what I'm used to and we don't get a chance to go in them very often. Especially since we usually don't get to go with the guys for switching.

When I was at a smaller shop, I rode with the troubleman a lot, and got to see a bunch of switching, so it made everything make a little more sense. I wish they'd do it here, but it's a bigger, less organized shop so we don't get to see it as much.

Trojan
05-09-2011, 12:56 AM
Thanks for the info on the 480 bank. That's pretty cool

I understand about testing phase to ground to determine which phase does have the ground on it. But go before that step. How was it determined there was a ground on the line to begin with? What symtoms are there?

Two too many...

Gotten calls from customers who found grounded phase when they were testing to repair or connect equipment.