Hi Brian:
> Related note - have been running long-term (day 22) test, inspired by > another PSTC thread, where a unit is continually subject to > 1500Vac D/E > withstand. At irregular intervals, or until the boss tells me to stop > wasting time, I remove the unit from hi-pot and perform IR > measurement. Some years ago, I did this same test. (I turned off the test overnight as I did not want a failure when no one was present.) The test ran about 2 weeks before I got any results. I describe the results as a "stutter" in the test -- sometimes a pass, sometimes a fail. Solid insulation failure usually starts with partial discharge that gradually builds a small carbon path in an insulation void, or between two sheets of insulation. The carbon path can't handle much current, so the hi-pot voltage will often burn the carbon path open, only to grow again. So, you get a fail (trip) and then test again and get a pass -- for a while. In some cases, the current in the carbon path may not be high enough to trip the hi-pot tester, in which case a before and after IR test may give an idea of whether the insulation will fail. Maybe the IR tester will have much less current, and allow the resistance measurement. > Are there reasons why IR is not considered a 'standard' Type Test? Depends on what your motives are. When is an insulator a resistor, and when is a resistor an insulator? In a past career, we worked with very high impedance, high- voltage circuits. The insulation resistance measurement was very useful; the high-pot test was not so useful. In safety, insulation is the principal safeguard against electric shock. The electric strength of the insulation is the key parameter for preserving the insulation against catastrophic failure (which would lead to electric shock). The IR test is not so useful for predicting whether or not the insulation is likely to fail. Some safety proponents have pushed for partial discharge testing as the measure of whether or not the insulation will withstand the applied voltages without failure. PD testing is not easy, and requires sophisticated test equipment. Best regards, Rich - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
