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#166101 - 07/12/07 05:13 PM Hi-Pot testing 15kV Cable
windmiller Offline
Junior Member

Registered: 12/05/06
Posts: 43
Loc: Alaska
Hi,
I am having a ground fault on a 15 kV cable. I was wondering if anyone has ever heard of hi-potting a cable that is still terminated to the bus?

The ground runs through the CT and the breaker is tripping on reset.

Thanks for any information or tips on hi-potting.

great website and members.

regards,
windmiller
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#166284 - 07/17/07 07:42 AM Re: Hi-Pot testing 15kV Cable [Re: windmiller]
XtheEdgeX Offline
Member

Registered: 04/17/05
Posts: 127
Loc: Florida
Never have. The cable needs to be free and clear on each end to hi-pot it correctly.

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#166295 - 07/17/07 09:59 AM Re: Hi-Pot testing 15kV Cable [Re: windmiller]
George Corron Offline
Member

Registered: 05/16/01
Posts: 728
Loc: Lorton, Va USA
If you don't remove it, you will be hy-potting buss and all simultaneously. Not a big problem, but you won't know if the problem is cable or buss.

Try an ohm-meter first, it will tell you more about how far away your problem is, but if the ohms are high phase to ground, your still stuck trying to locate. You may need to find a "thumper" if it is underground.

The hy-pot will tell you if you have a bad termination, if the cable has been in service awhile and just started tripping out you will likely see track marks near the term if that is the problem.

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#166299 - 07/17/07 11:21 AM Re: Hi-Pot testing 15kV Cable [Re: George Corron]
ghost307 Offline
Member

Registered: 05/09/05
Posts: 876
Loc: Chicago Illinois USA
If you try to hi-pot the cable while it's still connected and end up hi-potting the equipment, how with the buss,relays, etc. react to that test voltage?
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#166300 - 07/17/07 12:27 PM Re: Hi-Pot testing 15kV Cable [Re: ghost307]
Zog Offline
Member

Registered: 09/13/05
Posts: 116
Loc: Charlotte, NC
Every cable specification out there does not recommend DC hipotting service aged (>5 years) cables. DC hipot is considered a destructive test and will most likely damage the cable. Ghost307 is right about disconnecting the cable from the bus, the cable should be disconnected with corona supression before any overpotential test.

You can locate your problem without a shutdown with an online Partial Discharge test, or if shutting down is not a major issue a VLF or Tan Delta test would be more appropriate.

When is the last time you tested your relays? What type of relays are they? What indications are you getting? What type of cable?
_________________________
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#166338 - 07/18/07 09:31 AM Re: Hi-Pot testing 15kV Cable [Re: windmiller]
George Corron Offline
Member

Registered: 05/16/01
Posts: 728
Loc: Lorton, Va USA
He did not state WHAT level he was high potting to, a fairly low hy-pot will not harm an older cable.

He will want to remove any PT fuses prior to high pot. Any equipment connected to that buss is going to be rated for system voltage or is already self destructed. I would suggest hy-pot to system voltage only.

I'd still do a thorough visual of the buss and terms to check for tracking. The problem may be painfully obvious.

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#166343 - 07/18/07 11:28 AM Re: Hi-Pot testing 15kV Cable [Re: George Corron]
Zog Offline
Member

Registered: 09/13/05
Posts: 116
Loc: Charlotte, NC

It dosent matter WHAT level he is hipotting to. The ICEA, and both IEEE 400 and IEEE 576 do not recommend DC hipotting service aged cables.

In addition the IEEE 400 states “even massive insulation defects cannot be detected with DC at the recommended voltage levels”. If massive insulation defects cannot be found at recommended levels what do you expect to find at a "Fairly low" level?

Also the ICEA allows for reduced voltage DC testing for the first 5 years and no DC testing after 5 years and states that DC testing of service aged cables can lead to early failures.
_________________________
MV/HV Testing Specialist, "BKRMAN"

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#166352 - 07/18/07 05:14 PM Re: Hi-Pot testing 15kV Cable [Re: windmiller]
George Corron Offline
Member

Registered: 05/16/01
Posts: 728
Loc: Lorton, Va USA
He is attempting to identify a problem, not commission a cable. The problem will show with a low level test, a megger, or likely, as I said before, an ohm meter.

He may want to consider an AC test as opposed to your DC.

You are of course right, better to do nothing, or hire a third party to do a tan delta test as opposed to rectify the problem.



Edited by George Corron (07/18/07 05:14 PM)

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#166375 - 07/19/07 05:03 AM Re: Hi-Pot testing 15kV Cable [Re: George Corron]
Zog Offline
Member

Registered: 09/13/05
Posts: 116
Loc: Charlotte, NC
"He is attempting to identify a problem, not commission a cable"

A DC hipot would be fine if he was commisioning a cable, A PD or Tan delta test is a condition assesment test.

"as I said before, an ohm meter"

You really think putting 5-7V across 15kV insulation will tell you anything but "O.L."???? That wont even charge the insulation. A DAR test with a 5000V megger may provide some useful info if you want a quick easy test.

"He may want to consider an AC test as opposed to your DC"

Thats what I have saying all along.
_________________________
MV/HV Testing Specialist, "BKRMAN"

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#166381 - 07/19/07 09:50 AM Re: Hi-Pot testing 15kV Cable [Re: Zog]
gibbonsseabee80 Offline
Member

Registered: 10/10/05
Posts: 40
Loc: Chesapeake, VA
Im like the eighth response lol. I have never heard of that method. We hi-potted a set of cables about six months ago. We pulled the load break elbows at the other end (all free from equipment and sensors) and taped Jelly jars on the end of the load breaks..to ensure they were completely isolated from any ground.
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