I think it depends on the construction of the transformer and also if the air gap is on a surface as opposed to being only in the air. This is not the case for many transformers I have seen. On the first supply I started testing, its breakdown characteristics have changed quite a bit over my testing. It acts quite differently now than originally. I don’t have a Hi-Pot tester to check the supply.
Many transformers I have looked at over the years have no air gap, just wire enamel and a paper like material between windings which is adequate at the start. Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email: [email protected] Website: http://dsmith.org ________________________________ From: Richard Nute <[email protected]> Sent: Thursday, February 27, 2025 11:27:30 AM To: doug emcesd.com <[email protected]> Cc: 'Pete Perkins' <[email protected]>; [email protected] <[email protected]> Subject: RE: major safety issue possibly affecting 20% of the electronic devices in use Hi Doug: Thanks for your response and especially your paper. Thanks to Figure 1, I am no longer alarmed by a possible breakdown of insulation between primary and secondary. In Figure 1, I see the set-up: NkdkJdXPPEBannerStart Be Careful With This Message >From ("Richard Nute" ><[email protected]>)<https://godaddy.cloud-protect.net/email-details/?k=k1&payload=53616c7465645f5f7a8501fdebf05b82472467f6ee236ff2525271ff2883c89137283345899be5ac2fe4423e728d1032fd43b4004cee5a96bd6cc9707032d1eae62815c69888def3dbbfe2fe1e10e2e4a1fc3a13d810094fbcea80f43d27d54edb4ba3937f754bfca38100240473576de1d8f603e9943c360560529733582bd222c873cf34f3991ee3707f260f4f1bd0258d6b26aa12a17b3771a12f6f59cee2c9c98cc2481e035072b11fb52448543b2e093036c1499e271f7812b96a3e6267fc7988551fe77562ff9fff2fb94550a26d905987762d28975d073431802603a1> Learn More<https://godaddy.cloud-protect.net/email-details/?k=k1&payload=53616c7465645f5f7a8501fdebf05b82472467f6ee236ff2525271ff2883c89137283345899be5ac2fe4423e728d1032fd43b4004cee5a96bd6cc9707032d1eae62815c69888def3dbbfe2fe1e10e2e4a1fc3a13d810094fbcea80f43d27d54edb4ba3937f754bfca38100240473576de1d8f603e9943c360560529733582bd222c873cf34f3991ee3707f260f4f1bd0258d6b26aa12a17b3771a12f6f59cee2c9c98cc2481e035072b11fb52448543b2e093036c1499e271f7812b96a3e6267fc7988551fe77562ff9fff2fb94550a26d905987762d28975d073431802603a1> Potential Impersonation The sender's identity could not be verified and someone may be impersonating the sender. Take caution when interacting with this message. NkdkJdXPPEBannerEnd Hi Doug: Thanks for your response and especially your paper. Thanks to Figure 1, I am no longer alarmed by a possible breakdown of insulation between primary and secondary. In Figure 1, I see the set-up: Pulse generator -> cable -> probe -> cable -> power supply -> ground Within the power supply: Secondary circuits -> solid insulation, air insulation, EMI capacitance, transformer winding inductance -> primary circuit >From a safety point of view, I see a complex capacitance coupling current (and >possible inductive effects of the transformer windings) to the primary >circuit. But, I don’t perceive any dielectric damage. Thanks again, Rich Ps: I would expect a difference in the current waveforms between Figures 1 and 2 configurations. From: doug emcesd.com <[email protected]> Sent: Wednesday, February 26, 2025 8:27 PM To: [email protected] Cc: 'Pete Perkins' <[email protected]>; [email protected] Subject: Re: major safety issue possibly affecting 20% of the electronic devices in use Hi Rich and the group, Accidentally hit send on the last one. Here is a link to the paper: https://emcesd.com/pdf/An_Unusual_Source_of_Multiple_ESD_Events_in_Electronic_Equipment_final.pdf<https://urldefense.proofpoint.com/v2/url?u=https-3A__emcesd.com_pdf_An-5FUnusual-5FSource-5Fof-5FMultiple-5FESD-5FEvents-5Fin-5FElectronic-5FEquipment-5Ffinal.pdf&d=DwMFAg&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=tP4ynwqzldJBFpq8iMilqEevrzZeqxneKUW-xaGcWoqbmd9pw8D2X6uhVIqHLn3Y&s=RaBr8PHRC7w6R7th2YG58KCbStWnsaXTOYaftCWCVLo&e=> I think resonance in the EMI filter with a Q of 5 could do it. I was in the lab today and determined the effect is due to the long tail on ESD and EFT events, not the fast rise time. I got some very good scope shots of the phenomenon today. In the past I have observed the effect in both small two wire supplies and even in a 1.5 kW supple in a semiconductor fab. I did not realize the safety implications when I wrote that paper. Later on and I started to think how that phenomenon could happen is when the light bulb went off in my brain. I plan to build a suitable pulser with no moving parts to wear out to see if I can induce damage. I can build such a pulser in about an hour with parts I have laying around. It will produce pulses with a few ns rise time and a 300-500 ns fall time with an amplitude of 1200 Volts or so, a very easy thing for me to assemble. An ESD gun will work but with a lot wear on the HV relay to make 100,000 pulses. Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email: [email protected]<mailto:[email protected]> Website: http://dsmith.org<https://urldefense.proofpoint.com/v2/url?u=http-3A__dsmith.org&d=DwMFAg&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=tP4ynwqzldJBFpq8iMilqEevrzZeqxneKUW-xaGcWoqbmd9pw8D2X6uhVIqHLn3Y&s=1i3LVauSapb-sFcpt0k7VIs85Bqx1xUSa1qeYh-4fXE&e=> ________________________________ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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