Hi Pot, Hi Amp

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fifty60

Senior Member
Location
USA
I am familiar with doing ac/dc withstand (hi-pot) tests on standard equipment at ambient conditions. I am curious about doing the same type of tests on equipment that carries a lot of current, for example a connector that carries 400A, the hi-pot test for this type of equipment would be very different than a connector that carries 5A, right?

I've never really had to think about the current the equipment is carrying, but at hi amps the heat generated would have to be taken into consideration, right? The test at normal ambient conditions (75 F) would not be valid if the equipment sees extreme temperatures due to the current across it, right? Would the hi pot test have to be done with the equipment at the worst case temperature to be valid?
 

zog

Senior Member
Location
Charlotte, NC
Hi-pot is testing the insulation strength and has nothing to do with current rating, that's what overcurrent tests are for.
 

fifty60

Senior Member
Location
USA
Understood, but wouldn't running under full load for an hour potentially change the temperature of the insulation?
 

fifty60

Senior Member
Location
USA
How do you determine the design temperature for the insulation? Is there a table that has insulation type, voltage rating, and temperature rating?
 

fifty60

Senior Member
Location
USA
The withstand tests I am familiar with require operating the machinery for 4 hours with the worst case source of ventilation blocked. This will allow the machinery's insulation to reach the worst case single fault operating temperature. Once it has reached the worst case single fault operating temperature, it is then OK to do the dialectric withstand testing.

This makes sense to me. I am trying to determine if it is reasonable to conclude that performing the Hi-pot test at ambient non-running conditions is really not a good way to do the type tests, and that the heat is a factor in the effectiveness of the insulation.....does this sound like a reasonable conclusion?
 

topgone

Senior Member
The withstand tests I am familiar with require operating the machinery for 4 hours with the worst case source of ventilation blocked. This will allow the machinery's insulation to reach the worst case single fault operating temperature. Once it has reached the worst case single fault operating temperature, it is then OK to do the dialectric withstand testing.

This makes sense to me. I am trying to determine if it is reasonable to conclude that performing the Hi-pot test at ambient non-running conditions is really not a good way to do the type tests, and that the heat is a factor in the effectiveness of the insulation.....does this sound like a reasonable conclusion?

You said you do hipot test, may we know how much leakage current is set on your test equipment for it to indicate failed equipment?
 

fifty60

Senior Member
Location
USA
It has been a while since I've done one, but if I remember correctly I was using the "breakdown" setting on the hi pot tester. Not sure if that is the correct wording for the setting, but you could put but in a numeric setting, and there was a general "breakdown detected" setting...or some wording like that....it was the exact wording in the standard I was using, and was also the same setting UL used to test the equipment...this is different equipment however..
 

fifty60

Senior Member
Location
USA
Why does insulation resistance decrease with temperature? I thought the electrons would move quicker with the rise in temperature, increasing the resistance to the travel of electrons through the material. Copper, for example, increases in resistance at temperature goes up. Insulation though, decreases in resistance as temperature goes up...I'm having a hard time understanding why...
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Why does insulation resistance decrease with temperature? I thought the electrons would move quicker with the rise in temperature, increasing the resistance to the travel of electrons through the material. Copper, for example, increases in resistance at temperature goes up. Insulation though, decreases in resistance as temperature goes up...I'm having a hard time understanding why...
High temperature makes the "stationary" electrons in the metal move around more and increase the chances of interactions​ with the "mobile" electrons, slowing them down and dissipating energy.
In an insulator there are no mobile (free) electrons, so increasing the temperature just makes it easier for a few of the bound electrons to break lose and conduct current.

Sent from my XT1585 using Tapatalk
 
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