List-Post: [email protected] Date: 11 Jul 96 20:21:26 EDT From: "Egon H. Varju" <[email protected]> To: "INTERNET:[email protected]" <[email protected]> Cc: IEEE <[email protected]> Subject: Re: Transformer requirements in IEC950
Hi Jim, 1. To the best of my knowledge, you would have great difficulties convincing ALL the agencies that any form of varnish impregnation reliably complies with Clause 2.9.7. This is not to say that the concept is invalid; it's just that many agencies are not convinced ... 2. On the other hand, if you have a reliable and consistent varnish coating, there is a better chance that you can convince the agencies to accept Pollution Degree 1 spacings. Of course, this means that you have to prove that the coating is even, and won't shrink or crack after aging. So you're still in for a bit of a battle. In conclusion, all 3 answers you got are technically correct. But for practical purposes, you can save yourself a lot of grief by taking Rich Nute's advice and ignoring the varnish impregnation. BTW, I think Rich's finger slipped on the keyboard. If you need SELV secondary, then the insulation system options he gave you are correct, except for the one that says Basic-core-Basic. This should have read Basic-core-Supplementary. :-) Egon Varju ============================================================================ I wouldn't mess with varnish either if there wasn't any need to, but sometimes the 10 pounds doesn't go into the five pound can any other way. Major battles have been fought around here over thousandths of a millimeter. UL's yellow book lists varnishes under OBJS2 and OBOR2. FWIW, John C. Dolph Co. HI-THERM BC-359 has been used here with good results. Regarding dipping versus vacuum .... it's a little hard to ensure that the varnish will get into the places where it should unless all the trapped air is sucked out using a vacuum. If everything that needs the varnish is exposed and not buried behind something else, dipping would probably work. - Mike Rains
