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Re: Hi-Pot testing 15kV Cable [Re: gibbonsseabee80] #166402 07/19/07 11:23 PM
Joined: Jul 2004
Posts: 129
H
hypress Offline
Member
Did I understand you that you closed a breaker in on a faulted cable without testing it first. To say that is a extremely dangerous pratice is puting it mildly . Someone should loose their job over that.I know I would.
Our procedure is that on 480 volt you are NOT ALLOWED to close a breaker if it has triped on short time delay unless the circuit has been megged and you are only allowed to close it ONE TIME without on a long time delay trip without megging the circuit.
On anything above 480 you must megg or hipot on a overcurrent trip of any type plus the breaker must be serviced an if it is a oil circuit breaker the oil must be changed. I neglected to say that that if a 480 breaker trips on short time it must be serviced.

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Re: Hi-Pot testing 15kV Cable [Re: gibbonsseabee80] #166408 07/20/07 01:19 AM
Joined: Dec 2005
Posts: 858
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RODALCO Offline
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You need to have both ends of the cable clear from any bus, or termination or lightning arrestor.
A 5 kV megger test is acceptable and does not damage an HT cable.
By testing each phase at the time to ground and testing phase to phase a good overall idea of the condition of the cable can be found.
In your case with a ground fault you probably have a < 1 M.ohm reading on one of the phases.
If all phases give equal readings say 500M.ohms or more the cable may be ok and the OCB or lightning arrestors may need to be checked.

Prior to commisioning after repair a VLF test is the best way and does not damage new or aged cables.
We, in NZ, VLF test aged 11 kV cables at ± 17 kV. so a 15 kV cable requires about ± 23 kV for a VLF test. check what your POCO requires.


The product of rotation, excitation and flux produces electricty.
Re: Hi-Pot testing 15kV Cable [Re: RODALCO] #166422 07/20/07 08:20 AM
Joined: Sep 2005
Posts: 120
Z
Zog Offline
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Hypress, your company policy is following exactly what OSHA 1910.342 says about re-energizing circuits after a protective action.

This is probably the most violated OSHA article for power system operations.


MV/HV Testing Specialist, "BKRMAN"
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