What the hell am I looking at?

[DeeKay]

Alright here's a new one for me. So yesterday I went out to Bum-f$%@ nowhere Colorado to start one of my idle compressors and noticed some odd voltage numbers on my pre-startup checks.
480V 3phase dedicated service from POCO , no loads, main breaker open, readings taken from line side of breaker. POCO meter shows no phase loss.
Here's what I got:
L1-L2: 283V
L2-L3: 5V
L1-L3: 288V

L1-GND: 286V
L2-GND: 0V
L3-GND: 4V

So then I run down the road to another site that I know has good power, (also different utility) Just to verify my meters and sanity. Meters check out so I go back to the compressor site to double check my original readings. This time around I get the numbers below:
L1-L2: 204V
L2-L3: 38V
L1-L3: 166V

L1-GND: 286V
L2-GND: 98V
L3-GND: 128V

The only thing I can think is that there is maybe a ground fault between the pole and my main breaker and the conduit is probably full of mud and water as well. Anyone have any other ideas?

 

[Bert_]

Stuff is running off one or both of these services?

Volt meter checks good?

 

[DeeKay]

Stuff is running off one or both of these services?

Volt meter checks good?

Meters verified on a known good power source, both checked out (T5-1000 and 87-V) That's why I ran down to the other site; different power company down there so I could double check that my meters were working.

It's only the one service, second set of readings is just from a couple of hours after I checked voltage the first time around. That's the weirdest part, not only do the voltages make zero sense but they changed as well.

 

[Terry D]

I would check with a different meter. Is this a delta or wye system. When you say ground, do you mean a neutral

Like bert said, is stuff running off the services? Equipment would not opererate off those voltages correctly

 

[Bert_]

Meters verified on a known good power source, both checked out (T5-1000 and 87-V) That's why I ran down to the other site; different power company down there so I could double check that my meters were working.

It's only the one service, second set of readings is just from a couple of hours after I checked voltage the first time around. That's the weirdest part, not only do the voltages make zero sense but they changed as well.

Got it. I read as both services were reading like that.

You must have a wye with only one good phase. I would be looking for open fuses on the primary. They are easy to spot with a quick walk around the poles. A call to the power company would be the first thing to do.

 

[alfredeneuman]

You must have a wye with only one good phase. I would be looking for open fuses on the primary. They are easy to spot with a quick walk around the poles.

I've had the same problem not with the service, but with a 3Ø, 120/208V distribution transformer.
The problem ended up being a bad fuse in the 480V disconnect feeding the transformer.

 

[DeeKay]

I would check with a different meter. Is this a delta or wye system. When you say ground, do you mean a neutral

Like bert said, is stuff running off the services? Equipment would not opererate off those voltages correctly

I've checked with two different meters. Both multimeters were verified on a known good 480v supply. It's solidly grounded wye which explains some of the readings close to 277. The first set of readings sort of makes sense to me, but the second set still has me scratching my head....why did they change after a couple of hours?
checked phase to phase and phase to ground...there is no neutral.
No nothing was running, this is a dedicated service to my equipment and my main breaker was open.

Got it. I read as both services were reading like that.

You must have a wye with only one good phase. I would be looking for open fuses on the primary. They are easy to spot with a quick walk around the poles. A call to the power company would be the first thing to do.

I thought the same but all three fuses look good up on the poles, no tails hanging and all are seated. Plus POCO's meter says it has all three phases. The power company doesn't work fridays or weekends out there apparently so they're coming out to check things on their end Monday. I guess if their stuff checks out then there must be a problem under ground somewhere.

thanks all!

 

[Bert_]

Two lines are basically floating. It's why the volt readings are weird.

The one that measures 286v is solid that wire, transformer, fuses are all good. 286v is 277v. It's going to be higher without any load.

 

[wyliesdiesels]

What is the make and model on the PoCos meter? may not have phase loss detection so if it reads any voltage, it will think all 3 phases are good.

sounds to me like you lost 2 legs underground. would be a PoCo issue.

why dont they work on weekends? what if a residence looses power? no service all weekend?

 

[Terry D]

I agree, sounds like you lost 2 phases from the utility

 

[ddawg16]

What is the make and model on the PoCos meter? may not have phase loss detection so if it reads any voltage, it will think it is good.

sounds to me like you lost 2 legs underground. would be a PoCo issue.

why dont they work on weekends? what if a residence looses power? no service all weekend?

What he^^ said

 

[TRWham]

I would guess PoCo XFMR is TU.

 

[Milton Shaw]

You have two legs dead and feedback from a load on the first leg is giving different voltages due to different resistances in the load that is on. Turn off all the breakers and then see if you have any voltages on the other two legs. Also make sure that is not phantom voltages from induction from the wires running close together. Some Fluke meters have a "Low Z" setting that has enough resistance to ignore the phantom voltages. Even a couple of light bulbs or ballasts could be on and giving that kind of readings from feedback.

 

[DeeKay]

You have two legs dead and feedback from a load on the first leg is giving different voltages due to different resistances in the load that is on. Turn off all the breakers and then see if you have any voltages on the other two legs. Also make sure that is not phantom voltages from induction from the wires running close together. Some Fluke meters have a "Low Z" setting that has enough resistance to ignore the phantom voltages. Even a couple of light bulbs or ballasts could be on and giving that kind of readings from feedback.

My main breaker is open and this is a dedicated feed. So unless there is a break or bad insulation under ground somewhere between the pole and my main there's no load anywhere and nowhere that could feed back. That wouldn't surprise me in the least though, it's pretty swampy out there right now and I guarantee that conduit is full of mud and water. Whoever ran this service did a pretty poopy job of it.

I'm still not quite grasping why the voltages changed from the first time I measured to the second time when no loads or other conditions changed... I guess it could just be ghost voltages like you said so I'll try that LoZ if I make it back out there before PoCo gets to it, I always forget my 87-V has that feature.

What is the make and model on the PoCos meter? may not have phase loss detection so if it reads any voltage, it will think it is good.

sounds to me like you lost 2 legs underground. would be a PoCo issue.

why dont they work on weekends? what if a residence looses power? no service all weekend?

I didn't pay much attention to what kind of meter it is, but that's a good point.
I'm not sure why they don't work weekends, I thought it was weird too when they told me that. I guess unless it's a true emergency like a hospital or something they don't worry about it until Monday and you're **** out of luck. The reliability and power quality is also really really really bad out there in eastern CO. It's sort of the wild west no rules type stuff with them. We even had them reverse phases on us one time after an outage...good thing that compressor has phase monitoring I guess.

 

[Innovate1]

Maybe some bad connections that aren't completely open but just high resistance. Had that happen on an overhead line to a house where the neutral connection went bad. Depending on what was on one side would go higher and the other lower. Poco just replaced the connector. Any connections on this that are out in the weather? How old is the feed?

 

[DeeKay]

Maybe some bad connections that aren't completely open but just high resistance. Had that happen on an overhead line to a house where the neutral connection went bad. Depending on what was on one side would go higher and the other lower. Poco just replaced the connector. Any connections on this that are out in the weather? How old is the feed?

That wouldn't surprise me either. It's about 15 years old, pretty extreme weather out there most of the time. 70mph winds, rain, hail, hot summers, cold winters you name it, they get pretty much everything besides hurricanes out there.

 

[DeeKay]

UPDATE. Turns out there's a 1000A fused disconnect switch between the pole and my main hiding in a shack that wasn't on the one-line. One phase completely open, one phase partially open. Time to propose phase monitoring for the whole site instead of just the main motor.
As always, thanks for the help.

 

[wyliesdiesels]

UPDATE. Turns out there's a 1000A fused disconnect switch between the pole and my main hiding in a shack that wasn't on the one-line. One phase completely open, one phase partially open. Time to propose phase monitoring for the whole site instead of just the main motor.
As always, thanks for the help.

Or how about changing out the fused disconnect to an MDP w/ a 1000a breaker. That way if it trips, all 3 phases will be disconnected.

Now you should also figure out why the fuses blew....

 

[DeeKay]

Or how about changing out the fused disconnect to an MDP w/ a 1000a breaker. That way if it trips, all 3 phases will be disconnected.

Now you should also figure out why the fuses blew....

I wish all of my feeds out there were on breakers instead of fused disconnects, but the feed is the customer's responsibility and the contracts only specify the type of service and not the type of OCP....pretty dumb if if you ask me.
My main has an unused shunt trip option, I think it would be cheaper to install a phase monitor to trip my main when there's loss or imbalance. Why they never opted for it in the first place is beyond me...they're not all that expensive.

 

[jlv03]

Depending on the main breaker's configuration/, if your main has an electronic trip unit with a voltage relaying package you may be able to go with phase imbalance on the breaker itself.