Cable Megger deepwell

[jdping2]

I have a customer that had a 50 hp 3 phase 480 volt deepwell installed, motor is 600 feet below grade, fed with 3/0 copper drop cables , all of which were installed by well contractor. There is an existing square d wellguard combination starter that controls the new deepwell, the starter has a pumpsaver unit in it which up until 3 weeks ago, the starter was feeding an adjacent well which is now being decommisioned. The well contractor brought in a rental generator to test the recently installed deepwell and ran the motor for about 3 hours - this was done without a starter or overload relay, straight connection from generator (200amp 3 pole 600 volt main breaker), I was surprised that they ran a new motor directly to the generator without a starter, although did not say anything to them. I was also expecting the breaker to trip which it did not ( what about inrush current ?).

Anyways, prior to integrating the new deep well motor into existing controller I performed a megger test of the new deepwell cables which are connected to new 50 hp 480 v deepwell motor on one end and not connected to anything topside, Fluke 1587 FC , 1000v test range and heres what I found - A to ground 0.0m @1vdc, B to ground 0.0m @ 1vdc, C to ground 2.2G @ 1047 vdc. Then I checked between phases A to B 0.0m @ 1 vdc, A to C 2.2G @ 1047 vdc, B to C 2.2G @ 1047 vdc.

I am embarrased to admit that I do not know how to interprit the phase to phase readings, It is clear to me that the phase to ground readings indicate that A and B phase are both shorted to ground , and that C phase is clear to ground. According to the well contractor, there are no start or run capacitors in the deepwell motor. Grundfos No 92530624 MMS6NST50 . after presenting the megger readings to the deepwell contractor, he has stated that they weill be removing the deepwell motor to fix the issues, my main question here is - should there be any resistance between phases? Its Killing me that I can not figure this one out......

 

[petersonra]

I don't know what it means either.

Shouldn't it read zero phase to phase if it is a normal motor and open phase to ground?

I don't think a 50 hp 480 V motor will trip a 200 amp mccb unless something is wrong.

 

[Dsg319]

I have a customer that had a 50 hp 3 phase 480 volt deepwell installed, motor is 600 feet below grade, fed with 3/0 copper drop cables , all of which were installed by well contractor. There is an existing square d wellguard combination starter that controls the new deepwell, the starter has a pumpsaver unit in it which up until 3 weeks ago, the starter was feeding an adjacent well which is now being decommisioned. The well contractor brought in a rental generator to test the recently installed deepwell and ran the motor for about 3 hours - this was done without a starter or overload relay, straight connection from generator (200amp 3 pole 600 volt main breaker), I was surprised that they ran a new motor directly to the generator without a starter, although did not say anything to them. I was also expecting the breaker to trip which it did not ( what about inrush current ?).

Anyways, prior to integrating the new deep well motor into existing controller I performed a megger test of the new deepwell cables which are connected to new 50 hp 480 v deepwell motor on one end and not connected to anything topside, Fluke 1587 FC , 1000v test range and heres what I found - A to ground 0.0m @1vdc, B to ground 0.0m @ 1vdc, C to ground 2.2G @ 1047 vdc. Then I checked between phases A to B 0.0m @ 1 vdc, A to C 2.2G @ 1047 vdc, B to C 2.2G @ 1047 vdc.

I am embarrased to admit that I do not know how to interprit the phase to phase readings, It is clear to me that the phase to ground readings indicate that A and B phase are both shorted to ground , and that C phase is clear to ground. According to the well contractor, there are no start or run capacitors in the deepwell motor. Grundfos No 92530624 MMS6NST50 . after presenting the megger readings to the deepwell contractor, he has stated that they weill be removing the deepwell motor to fix the issues, my main question here is - should there be any resistance between phases? Its Killing me that I can not figure this one out......

In my mind there should be very very low resistance between phases being they are all connected together via the motor winding and in a perfect world super high resistance to ground (2.2Gohms)

With that being said if one phase reads a short to ground I would expect them all too unless the winding is broke open somewhere?

 

[tom baker]

When you megged, did you verify nothing on contactor end to cause a low ohms? Sometimes I would disconnect leads on OL going to motor.
Your readings are suspicious. 600 ft is a lot of wire with considerable capactance, how long did you leave the Fluke connected?
What is the standing water level, ie how much water is above the pump?
Did the contractor use submersible pump cable? It has a jacket over the power wires and if the contractor was moderately careful the drop cables should be ok
Lastly, be there when they pull the pump, check the cable and splices to motor leads.
The motor lead will be much smaller than the 3/0 so look at that splice, I used reducing splices when I made those up, with HD heat shrink

 

[petersonra]

I looked at the manual. Not much help that I saw.

 

[tom baker]

The well driller I worked with liked me to use a roll of 33 on each splice and skotch kote as well. I had the old school hand crank meager and took a while to trust the Fluke. Later I used heavy duty heat shrink on the splices

 

[ptonsparky]

We would meg 1300 ft of direct bury with no issues. 600 shouldn't be a problem.

Wires should be removed from from lugs for best results