Failure of 11kV Cable
Failure of 11kV Cable
(OP)
I've just had a failure of an 11 kV cable in the connection box to the rear of a VCB. The cable is three-core, XLPE, armoured. The failure occurred after the point at which the cores had been separated. It looks to me like one of the cores was bent at too tight a radius; this is the only core for which the insulation was blown apart, at the bend. Does anyone have comments as to whether or not a tight bend is likely to damage the primary insulation and / or semi-conductive layer around the individual core, leading to failure? The duty is an indoor substation, so environmental conditions are not likely to have played any part in the failure.
Thanks in advance for you comments.
Regards,
Brian
Thanks in advance for you comments.
Regards,
Brian






RE: Failure of 11kV Cable
the semicon layer needs to be removed with special care and use of correct tooling .
whats the history of the cable ?
RE: Failure of 11kV Cable
Depending upon interest level, the cable manufacturer and termination-kit manufacturer may be contacted to obtain installation recommendations that could be used to demonstrate incompetence in cable installation.
RE: Failure of 11kV Cable
http://www.okonite.com/engineering/bending-ratios.html
RE: Failure of 11kV Cable
RE: Failure of 11kV Cable
It turns out that although the bending radius was indeed a little tight, the main cause of the failure was that the installing contractor "nicked" the primary insulation when preparing the connection!
Regards,
Brian
RE: Failure of 11kV Cable
RE: Failure of 11kV Cable
What is the warranty from the contractor? This is very exspensive for someone to eat.....
RE: Failure of 11kV Cable
Regards,
Brian
RE: Failure of 11kV Cable
Aside from the widely circulated industry buzz, I believe an experienced tester birdogging leakage current with reasonable caution during DC-overpotential testing will detect medium-voltage shielded-cable dielectric nicks in a heartbeat.
RE: Failure of 11kV Cable
But, argue the “safe” service-aged procedures until the cows come home.
RE: Failure of 11kV Cable
Dr. Professor Dean C.L. Wadhwa "Electrical Power System," John Wiley & Sons, 1991, Chapter 6 Corona, pages 135-149.
Method of Reducing Corona (Loss)
1. Large diameter conductors,
2. Hollow conductors, and
3. Bundled conductors.
RE: Failure of 11kV Cable
RE: Failure of 11kV Cable
Thanks. That's what I was thinking of doing for the other cables that were installed at the same time as the one that failed...I'll post results when I have them!
Regards,
Brian