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Topic Title: Megger Testing Vs HiPot Testing of 690V cables
Topic Summary: Correct Method
Created On: 30 December 2011 01:56 PM
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 30 December 2011 01:56 PM
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michaelfivey22

Posts: 27
Joined: 21 January 2004

Hi,

As you can probablt see from my other post I am try to work towards locating a fault somewhere in a power network on a ship. The obvious place for this fault would appear to be the 690V cables on the outgoing side of the breaker.

We have megger tested them at 2kV and shown no fault ph-ph or ph to ground.

A lot of people are suggestinjg a hi pot test but I am not so sure it would do any good or is even a suitable test for this type of cable.

Can any of you please point me in the direction of a relevant standard or even give me the summary of the relevant standard is not freely available on the net.

Until now a megger has always been suitable and accepted.

Also do any more advanced instuments exist suitable for testing cables such as the Baker winding tester?

Thanks for all the help

Mike
 30 December 2011 04:34 PM
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ArthurHall

Posts: 735
Joined: 25 July 2008

Hi Mike
Are the cables single core or multi core?
If they are singles there is no point in doing a phase to phase test.
The rule of thumb for test voltages is twice the working voltage plus 1kV for 15 minutes. So for 690V I would suggest 2380V phase to phase and 1800V for phase to earth. Although if it is an IT earthed system you have to allow for the full line voltage to earth. In short I would megger at 2.5kV.
If the cable has already passed a 2kV test I would say it is OK.
I am not sure what a hi-pot test is, my understanding is that it is just the american term for a pressure test.
From the other information you have given I still think the fault is within the breaker.
 31 December 2011 10:31 AM
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dlane

Posts: 690
Joined: 28 September 2007

Hi-Pot = High Potential Test = Pressure Test.

Not sure about it being American terminology but it is applied to HV rotating plant but I too am more familiar withthe term pressure test for cabling.

You can carry out partial discharge testing on cables but PD inception will generally start at around 3kV so I would think it would be a pointless test in your situation.

I am also not sure about applyimg a pressure test to an LV cable, HV cables have different construction methods to LV so I would be inclined to refer to the cable manufacturer and see what testing is applicable.

As with Arthur, if you have meggered the cables at 2kV then I would suspect that they are ok and your fault lies elsewhere.

Kind regards

Donald Lane
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