Possibly because standards provide an RMS level for AC dielectric and that 
never seems to be as high as 
the 'equivalent' DC dielectric test.  Since dielectric strength test 
checks for sufficient clearances, the DC test would be tougher on solid 
insulation.   Many standards say to us 1.41xAC for a DC test, presumably 
since any arc would occur at the peak of the AC test voltage. 

There is also some confusion about whether a leakage current limit should 
be imposed during dielectric tests.  It depends on what you think you're 
checking during routine hi-pot.   If creepage distances are compliant and 
you control what solid insulation is used as a critical component,  I 
think you need only look for breakdown, not leakage.

_____________________________________________________________________________________
 


Ralph McDiarmid  |   Schneider Electric   |  Renewable Energies Business | 
  CANADA  |   Regulatory Compliance Engineering 




From:
Brian Oconnell <oconne...@tamuracorp.com>
To:
EMC-PSTC@LISTSERV.IEEE.ORG
Date:
11/30/2011 09:47 AM
Subject:
[PSES] UL assessment of plastics - DC vs AC



Received a newsletter from UL. Said that they are looking into updating
standards to account for DC di-electric withstand vs AC. I can understand
that the physics of dc arcing and tracking could be different from ac, but
why would the dc di-electric withstand be more onerous than ac?

Perhaps they are mixing IR and di-electric withstand, which cannot be
considered a similar test.

Brian

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