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6 comments
Member

Join Date: Jun 2006
Posts: 6

Test Voltage For Insulation Resistance Test

09/24/2006 6:26 AM

Can somebody please explain to me? I want to know the appropriate test voltage to be used in carrying out insulation resistance test for a cable carrying voltage less than 50 volts. My reference standard (Shell DEP) only specify test voltage for cables with voltage carrying capacity as from 50 volts to 1000 volts as 500v (d.c).

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Pathfinder Tags: Insulation Resistance Test Voltage
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Anonymous Poster
#1

Re: Test Voltage For Insulation Resistance Test

09/24/2006 11:51 PM

i believe that the norm is twice the operating voltage - in your case 100v?

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Guru
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#2
In reply to #1

Re: Test Voltage For Insulation Resistance Test

09/25/2006 12:16 AM

I agree, that you test with twice the AD and DC voltages. If you have an idea of the freuency then switch the voltage with that frequency as cable impedance is frequency dependent. Cables have series inductance and shunt capacitance. Watch out for the peak current and have proper cable cunductor for the load. What you test without load is not same that you test with load. Engineering means all details that makes sense for the purpose, hence make a complete list, refer the test procedure of the standard and just follow them step by step.

Also look for relative humidity and air pressure and temperature norms. What you test in atomspheric pressure will fail in vacuum or low pressure. take care.

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Guru
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#3

Re: Test Voltage For Insulation Resistance Test

09/25/2006 6:21 AM

I would have said that as its extra safe low voltage a test for safety by insulation testing is hardly necessary.....

It all depends on why you want to test for insulation resistance?

Is it because its a signal cable and the signal requires high resistance? or maybe its a 1000 Amp supply cable that you want to check for premature failure of the insulation.....

Either way I usually specify a test voltage that will not damage the insulation or cause erroneous readings and that make the testing suitable and safe.....

When I say safe I mean if I'm testing a low voltage capacitor for leakage and its say 10,000 uFarad I would use as small a test voltage as practical, maybe 50 Volts and take precautions to allow full discharge and chargeing levels....

So overall, I would say if the insulation is rated as good up to and above 500 Volts there are plenty of standard instruments that can cope with that measurements i.e. even a hand cranked Meggar......

Just my thoughts...... John

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Join Date: Nov 2007
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#4
In reply to #3

Re: Test Voltage For Insulation Resistance Test

01/26/2009 8:40 AM

Is there a maximum amount of times you can perform this test? Meaning, and correct me if I am wrong, this is a destructive test. So if the first test is done at 500VDC you would perform the second test at say 25% less voltage i.e. 375VDC. After so many tests it is not recommend to perform any more?

Somewhere I believe I have learned this or heard it, I can't remember which. Is there some sort of guidance that suggests this?

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#5
In reply to #4

Re: Test Voltage For Insulation Resistance Test

01/26/2009 8:59 AM

Okay doing a little bit more research, I am almost certain that Insulation Resistance (IR) test is non-destructive and that the Dielectric Test is the actualy destructive test and needs to be reduced by 1/3rd for each sucessive test.

I am still looking for a standard or guidance for reference though.


Bill

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Guru
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#6
In reply to #5

Re: Test Voltage For Insulation Resistance Test

01/26/2009 9:28 AM

Leakage resistance in capacitor is voltage and temperature dependent. Hence, it is also dependent on the internal dissipated energy that heats up the capacitor. This complex parameter is obtained for a capacitor of known geometry and it is easy to reach to these parameters to other geometries.

Testing for operating voltages, may become destructive and hence, if you are looking for leakage resistance at high voltages, then that may be destructive also.

Capacitors also have memory effect and hence, those operated at low voltages for long time and never given a high voltage shock for months then they may resist such sudden change.

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