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#206489 07/09/12 08:36 AM
Joined: Jul 2007
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Okay fellas, I had a service call for a pump not running in a municipal water system. The pump is 10 hp submersible, down the hole about 200 feet, it will run about 3 minutes on comercial power then the phase loss monitor will trip and shut it down. There is a back up generator on site 40KW Kohler, start it throw transfer switch and all is right with the world. 3 phase 230 Delta with a high leg coming from the POCO, voltage reads as follows: A-N 121
B-N 190 C-N 121 A-B 236 A-C 255 B-C 241, based on those readings and amperage readings that varied 12 amps from leg to leg, I called in the POCO. Service man arrived, first told me there was nothing wrong on his end after measuring phase to neutral, I had him take the readings phase to phase then he agreed there was a problem.
Repair crew changes both pole pigs one 25KVA one 37.5KVA This doesent change a thing! Repair man says the pump motor is burnt up, to which I reply it has been running on the genset for 4 hours. I reset the phase loss monitor to give as much leeway as I dared, still wont run. Service man on the phone with engineer for a little while, check voltage again the A-C voltage is lower by about 5 volts, now the pump will run. When I left an engineer was supposed to ride the line the next morning, and "maybe adjust a regulator at the substation, but I still do not think it is our problem" How do you deal with bull headed utility people? Do you think there is something I missed, or should have done differently?


Jimmy

Life is tough, Life is tougher when you are stupid
Joined: Jan 2005
Posts: 5,316
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Well, I'd megger the pump and have the results on hand! You can be sure the PoCo rep will have test results from those trannys before he leaves the office.

It sounds like a pump problem to me as well .... you're getting way too much variation in your amp draw between legs.

I'm not sure the genny is providing the same power as the PoCo ... perhaps the genny is a simple Wye?

Joined: Jun 2004
Posts: 1,273
T
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Partial cross-short in pump windings... or a filthy contactor with pitting...

B-N high leg is WAY low..

How does A-N 121 + N-C 121 = A-C 255 ?

Double check with analog meter...

What were Kohler voltage readings?

Check neutral paths: Kohler vs Poco...

Last edited by Tesla; 07/09/12 12:39 PM.

Tesla
Joined: Jul 2007
Posts: 265
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Sorry guys, forgot to mention the voltage readings were taken with the pump OFF. The readings were about the same with the pump running. I did megger the pump motor and it was and is fine. Voltage and current are balanced and spot on when running on genset, but not on utility. Kohler voltage was A-B 239 A-C 238 B-C 239, taken with pump running, current was even at 24 amps per phase

Last edited by wire_twister; 07/09/12 05:17 PM. Reason: added info

Jimmy

Life is tough, Life is tougher when you are stupid
Joined: Jul 2004
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What is the voltage between the neutral and earth at the pump terminals when the pump is running on the power companies line?

It sounds like the earth neutral bond is not there, and the neutral voltage is wandering depending on what loads are turned on.

With a deep well like that, the voltage between the deep earth ground and the surface ground might be significant.

As an aside, are there any problems with corrosion that someone may have lifted a bonding wire to "cure" it?

Is the control power for the pump controller 120 V and is it referenced to earth?

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I will check that when I get back out there, but the trouble is with a 3 phase pump that does not use a neutral. There are several lights in and on the pump house, regardless of pump running or off these lights never flicker. The line to neutral voltages are rock steady, just the phase to phase is out of balance. No corrosion problems that i can see, this is an older well with a galvanized steel well casing which is bonded to the ground rod and the re-bar in the building slab. The control power is derived from a transformer inside the pump control, I guess they used a transformer to get a neutral because they did not pull one from the main load center.


Jimmy

Life is tough, Life is tougher when you are stupid
Joined: Mar 2004
Posts: 251
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Bad line caps on the Poco side. Power factor high. will cause some phase loss relays to trip. Also high harmonics can cause similar problems.

Joined: Mar 2004
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twh Offline
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I lost a phase at an oil satellite building with several pump jacks running off the same service and the only indicators were a bad phase voltage and one small pump that kept tripping the overloads. The other motors and the power factor correction capacitors kept everything running like a rotary phase converter. When the loads were all disconnected, the lost phase became obvious.

Joined: Jun 2004
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You were lucky...

Single phasing usually lets the smoke out.


Tesla
Joined: Jul 2007
Posts: 265
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Member
Update: Utility adjusted a regulator at the nearby substation, now all is good, pump is running fine,current has evened out at about 25 amps on all three legs, so I guess it was a utility problem, even if they denied it the whole time.


Jimmy

Life is tough, Life is tougher when you are stupid

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