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#67966 - 07/25/06 07:10 PM Insulation Capatence
hypress Offline
Member
Registered: 07/20/04
Posts: 129
Loc: Charleston WV
At work we heve 3 new meggers and they have a capatence test feature. This is not a capacitor test function but a insulation capatence. How can I relate insulation capatence to insulation quality. I know Doble testing measures capatence but it is done with AC.
THANKS
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#67967 - 07/25/06 07:21 PM Re: Insulation Capatence
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Hmm,
Now there is one for the books.
What brand/model meggers are they?
Are you sure you aren't referring to Insulation Resistance?.
Reason I say that, is because capacitance is the function of Insulation Resistance.

[This message has been edited by Trumpy (edited 07-25-2006).]
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#67968 - 07/25/06 07:44 PM Re: Insulation Capatence
hypress Offline
Member
Registered: 07/20/04
Posts: 129
Loc: Charleston WV
2 Megger BM21 and one Vangard and I am not sure of it's model number. I can say that all can output 5KV
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#67969 - 07/25/06 08:01 PM Re: Insulation Capatence
hypress Offline
Member
Registered: 07/20/04
Posts: 129
Loc: Charleston WV
The Meggers will gige you eather megohms or uF. the Vangard when it prints out it shows both megohms AND uF
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#67970 - 07/25/06 11:21 PM Re: Insulation Capatence
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
All along the "cable under test" there will be small capacitances, caused by the cable insulation, between cores, the longer the cable, the higher the capacitance.
This is why it is necessary to discharge the charge built up by meggering a certain cable.
One question, what type and voltage cables are you testing?.
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Let's face it, these days if you're not young, you're old - Red Green grin
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#67971 - 07/26/06 03:08 AM Re: Insulation Capatence
hypress Offline
Member
Registered: 07/20/04
Posts: 129
Loc: Charleston WV
We megger 600v building wire, 600v & 2400v motors,600v & 2400v draw out circuit breakers.Our 13.2KV equipment and underground is hipoted.
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#67972 - 07/26/06 05:51 AM Re: Insulation Capatence
Zog Offline
Member
Registered: 09/13/05
Posts: 120
Loc: Charlotte, NC
Capacitive charging current is one of the 3 leakage currents you are measuring with IR testing, it tends to decay pretty quickly as the cable is charged, we typically look at the capacitive element by calculating a DAR (Dielectric Absorbsion Ratio) which is determined by dividing the 60 second reading by the 30 second reading. Different ratios apply to different types of equipment but you should always have a DAR of at least 1.0 or more (>1.6 is excellent). >8.0 DAR however would usually means the insulation has become embrittled.
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#67973 - 07/26/06 09:19 AM Re: Insulation Capatence
Helectric Offline
Member
Registered: 01/07/05
Posts: 90
Loc: Brandon, SD
How often do you hi-pot your cables and what other equipment do you perform hi-pot testing on?

I'm just curious as this is "destructive" testing and many peaple don't use this method except when commissioning new equipment.
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#67974 - 07/26/06 09:54 AM Re: Insulation Capatence
Zog Offline
Member
Registered: 09/13/05
Posts: 120
Loc: Charlotte, NC
While I agree that DC hipot testing should be considered destructive, newer hipot methods are not and are acceptable for routine testing, VLF seems to be the leading canadite, but there is also PD ans Tan delta tests that are as effective and non destructive.
_________________________
MV/HV Testing Specialist, "BKRMAN"
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#67975 - 07/26/06 06:54 PM Re: Insulation Capatence
hypress Offline
Member
Registered: 07/20/04
Posts: 129
Loc: Charleston WV
Back again. We hipot our cables including the 600V cables as part of our comissioning process. If we have a in servic failur we will hipot those cables.
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