Hello Experts, In a previous life I spent quite a bit of time testing power-limited small transformers to North American requirements. One of the design strategies I encountered was the use of a special nylon coated wire(NEW), which would open safely and repeat-ably under fault conditions at a very specific temperature. The winding did not fail as result of current, but of elevated temperature. This process only took a few minutes under fault conditions, and samples invariably passed dielectric strength tests afterwards. Memory fails me as to the actual temperature measured in real-time, but I’d guess that the overall winding temperature would be 120 degrees or so when the winding became a fuse. This may be an option for your application, as the transformer fails safe, but has a high enough impedance that inrush is not an issue. I hope this helps. Brian IV
Best Regards, Brian Ceresney Regulatory Lead, Delta-Q Technologies Corp. Phone 1.604.566.8827 Confidentiality Notice: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. From: Richard Nute [mailto:[email protected]] Sent: October-31-16 11:22 AM To: [email protected] Subject: Re: [PSES] Low current Transformer OC Protection Hi Brian: It sounds to me as though you have an “impedance-protected” transformer. A common example in the USA is a doorbell transformer. The output can be shorted all day, and the transformer will not overheat (exceed the insulation temperature ratings). The transformer cannot draw or supply enough current to operate a fuse. And, it cannot get hot enough (above normal temperatures) to operate thermal protector. You can explain to the inspector that it is an impedance-protected transformer. He may not understand, so you will have to insist that he take your explanation back to his office for further consideration. Or, put a fuse in, knowing that its only purpose is to satisfy the inspector. Or, as Brian has suggested, use a certified transformer. 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 <[email protected]<mailto:[email protected]>> 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://www.ieee-pses.org/list.html (including how to unsubscribe)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]<mailto:[email protected]>> Mike Cantwell <[email protected]<mailto:[email protected]>> For policy questions, send mail to: Jim Bacher <[email protected]<mailto:[email protected]>> David Heald <[email protected]<mailto:[email protected]>> - ---------------------------------------------------------------- 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 <[email protected]> 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://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
