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Active Contributor

Join Date: Nov 2008
Posts: 13

Small Bluish Spark at Cable Lug

07/01/2013 11:12 PM

Hallo Sir,

I have a 22 KV indoor type cable end termination to a vaccum breaker coming from transformer (220/22 KV 25 MVA YY connected) which is about 80 meters away. Installation is only about two & half years old and is well maintained - protected from dust etc. There are 3x parallel cables of 300 sq mm & total load on all the cables is about 150 Amps (max). Two days back I noticed bluish sparking (continuously) on yellow phase of one cable at the edge of sleeve on the lug. Assuming this to be moisture problem, I heated the surrounding area and the specific point with hot air blower. This has reduced the intensity of the spark but not eliminated totally. Is it corona? what is the solution? request your guidance.

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Guru

Join Date: Oct 2008
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#1

Re: Small bluish spark at cable lug

07/01/2013 11:42 PM

More karma than corona, I think.

If it keeps up, all the secret smoke will leak out of the wire.

Solder it.

Corona discharge - Wikipedia, the free encyclopedia

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#2

Re: Small bluish spark at cable lug

07/02/2013 3:15 AM

1 - look with infra red camera if this is a bad electrical contact , it should be very hot (very little chances that this is the case..

2 - otherwith, this is partial discharge to earth or betwwen phases . What are the distances ? What shape of the edge of the lug ? Sharp angle ? if it is the case, can you de energize and smooth it ?

Anyway, all this smells like a non type tested design... be cautiouos, you may solove this problem and get another one ...

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#3

Re: Small Bluish Spark at Cable Lug

07/02/2013 11:43 AM

Blue spark going from the lug to where? From the lug to the sleeve itself? If so, that is typical of corona discharge and possibly tracking across moisture originally, but may now be tracking across a residual carbon trace. The next time it is de-energized, wipe and clean all of the surfaces with electrical cleaners.

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Join Date: Jun 2011
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#4

Re: Small Bluish Spark at Cable Lug

07/02/2013 11:50 PM

There was a forum on a similar issue not too long ago where the cable terminations to a generator failed several times.

The blue "spark" is a discharge and should not happen on a properly terminated cable in a dry atmosphere (indoor type). If not cured, the discharge will only get worse. Carbon tracks will be created in the insulated termination, and these will grow until there is a flash over initially to earth, but this will become phase to phase fault if there is exposed metal on the phases (which seems to be the case since you can see the lug).

1. Eliminate possibility of moisture in the cable box. (may not be visible as water drops). If there is an anti condensation heater in the switchgear make sure it is working.

2. Verify the termination is the correct one for the type of cable, and has been completed properly in accordance with the termination manufacturers instructions with all the stress relieving components properly installed. It might be best to have the cable reterminated.

3. Some terminations or cable boxes require an insulated (usually heat shrink) boot to be shrunk over the terminating lug/bolts. Check if this is recommended for your instaation.

3. Using appropriate high voltage tapes it is possible to insulate the lug/bolt which would reduce the stress at the lug/insulation interface.

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#5

Re: Small Bluish Spark at Cable Lug

07/04/2013 11:44 AM

Yes it is corona discharge and it will get worse if not mitigated which will result in a fault and/or catastrophic electrical failure.

Purchase and install/use the proper termination kit for the type and size of cable in use.

Make sure the term kit installer follows the manufacturer's installation instructions (IOM) correctly and completely without skipping any steps.

Shielded or non-shielded type? At this voltage level all cables should be shielded.

Are the drains installed correctly?

Is the semiconductor correctly removed?

Are the insulating sleeves of the correct type and length?

Are the insulation layers correctly "stepped" at the correct intervals?

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