I’m not completely clear about your questions but can only guess the manufacturer believes the higher than normal impedance looking back into the ac mains is a problem allowing the residual surge voltage at the generator input to be too high.
But according to standards, surge generator back filters are required to reduce the surge voltage that appears at the AC mains input to 15% of the surge voltage when the ac mains is disconnected. >From 61000-4-5 ed 2: The residual surge voltage on the power supply inputs of the decoupling network when the EUT is disconnected shall not exceed 15 % of the applied test voltage or twice the rated peak voltage of the coupling/decoupling network, whichever is higher. For the back-filter, this is the worst case and the generator must be able to withstand a voltage on the input of 15% of the peak surge – for most generators this is 6kV; therefore a peak surge voltage of 900 at the input of the back filter should NOT damage the generator. If the damage is being caused by a transient greater than 900 volts, I suppose it’s possible to set up some kind of ringing and overvoltage involving the back filter in the generator and the AC mains filter, but it seems pretty unlikely. The only thing that makes sense is that the generator input itself is not adequately protected or some protection component has failed allowing the 900V remnant voltage to get into the generator somehow. As for an overvoltage from the outside damaging the back-filter, I can’t see how this would happen. One would need a substantial transient (greater that the rated voltage of the generator) that could somehow get through the de-coupling caps or clamping devices at the input of the back – filter, then the chokes to cause some failure…. Bottom Line: AC mains filter shouldn’t matter; likely a generator problem. BTW – I have seen problems using some AC sources (other than the raw mains) to cause problems but typically not to the generator --- usually the voltage remnant of the surge causes a problem with the AC source – oscillations or shut-down. Anyway – I doubt the mains filter has anything to do with your problem. Best Regards, Michael Hopkins EM TEST USA 203 Wheeler Rd. Hollis, NH 03049 m.hopk...@emtest.com Office: +1 603 595 6420 Mobile: +1 603 765 3736 fax: +1 603 577 9192 - 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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com>
