<[email protected]>, Rich Nute <[email protected]> inimitably wrote:
>> >Of course, no one has shown that unacceptable >> >overheating will actually occur. >> >> Do you have any more such gems to contribute? What do you think happens >> to the total current through a capacitor when the applied voltage >> contains harmonics? What happens to the I^2R loss and the dielectric >> loss? What happens to hysteresis loss in motors and transformers? > >My assertion is based on the original reason for the >harmonic current emission standard, not the general >case for problems caused by harmonic currents. I >apologize for writing in such a way as to confuse the >general case of overheating due to harmonic currents >with the specific case of overheating in distribution >transformers. > >My recollection of the original reason for the >harmonic current standard was to prevent overheating >of distribution transformers on the public power >network. I have not heard that explanation put forward since 1991 by any electricity supply industry (ESI) expert on the IEC or the BSI committee. It is also not mentioned in the original rationale, Annex A to IEC 77A/164/CD (committee document, not in the public domain). But there must be increased hysteresis loss. > >Perhaps you can correct this recollection. If this >is not correct, then kindly disregard the following >remarks. > >Based on my probably incorrect recollection, my >assertion is that no distribution transformer in the >public power network has failed due to harmonic >current. I strongly suspect that that is not true in UK. There were many failures (some explosive) due to d.c. in the windings before we stopped using half-wave rectifiers in TV sets. I don't know about the situation from 1970 onwards: there have been failures but no specific cases undoubtedly due to harmonics have been cited by our ESI experts. > >I further recall that such failures were a prediction >based on the expected proliferation of products with >full-wave rectifiers, especially SMPS. The electric >power distribution representatives to the committee >predicted massive distribution transformer failures >due to harmonic currents by the year 2000 or >thereabouts. Therefore, the committee operated with >a high sense of urgency. > >Perhaps you can correct me on this recollection. You are correct, I think, about that, and I have said previously that the early predictions were pessimistic. Nevertheless, here I have about 3.5% voltage waveform distortion, in a residential area, which is more than I would like. The ESI has also been working under a threat from the Commission to impose 'quality of supply' requirements on it, since electricity is a commodity that should have quality requirements (see EN50160). This has made the industry VERY fearful of draconian fines being imposed for outages, and harmonics can be one cause that is avoidable, unlike severe weather. > >Can you tell us whether, at the time the work on the >standard was initiated, any such transformers had >indeed failed due to harmonic current overheating? >Or, have any such transformers failed due to harmonic >current since the work has been undertaken? > See above. But I don't think transformers are the big issue. In Europe, the MV network tends to be resonant at about 250 Hz - the fifth harmonic. The ESI has to be very careful that this does not result in over-voltage, because if an MV network fails, a large area is affected. The design of the European distribution networks makes them far less tolerant of harmonic currents that either the US or Japanese networks. This has only quite recently been demonstrated to the IEC committee: the evidence from outside Europe was not submitted previously. Capacitors and motors are the other things that are said to be particularly vulnerable. -- Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk Foxhunters suffer from tallyhosis. PLEASE do not mail copies of newsgroup posts to me. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
