Faulty cable

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siva

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Hi
Here(in Bahrain) we are making one new substation (11 kv/400 v,3 phase).The issue is that during hi-potential test of medium voltage cables(400 mm2 single core)one of the cable found faulty.ie when applying 22 kv for testing, after reaching 6 kv,voltage is not going up.The needle deflects at this point.what may be the reason?Any body can advice?
Another concern is that we tested this cable more than 8 times.Is this frequent hi-pot testings affect the cable quality?

Thanks in advance
Siva
 
Re: Faulty cable

siva,

We had dine the same testing with what you are doing now at 240 mm. sq. but multi core, 11KV - 415/230 V system. Its just like you are testing thru megger a 600 V cable at 1000VDC. The voltage won't go up if you have a leakage or a short.Normally, a cable test is being done before installation( On reel/cable drum) and after installation.
 
Re: Faulty cable

Your 11 kV cable or its terminations has a fault. The fault appears to be flashing over at 6 kV. Either replace the cable, or dismantle the terminations and retest to isolate the problem.

Depending on the type of cable insulation, repeated hi-pots can lead to cable damage. Cross-linked polyethylene insulation (XLPE) is prone to problems after exteneded DC hi-pot testing.
 
Re: Faulty cable

Faulty cable. The trick is to detect where the fault is and to cut and splice it, if the cable is too long.

There are various methods to find the location of the fault.
 
Re: Faulty cable

DC hipotting will damage a cable, if there is a void present a DC hipot will advance the formation of water trees. A much less destructive method is partial discharge testing, VLF, or Tan delta.
 
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