In message <[email protected]>, dated Fri, 22 May 2009, Ralph McDiarmid <[email protected]> writes:
>Why did the members of the EU decide that harmonic currents needed to >be controlled for appliances? It's not quite like that. (Is anything in EMC ever 'quite like that'?) The standard was developed in IEC, and American experts were, and still are involved (US, Canada, Mexico). But no US utilities have been involved for many years. In contrast, European and Canadian utilities are strongly represented, even though very much in a minority compared with load equipment experts. > I can see doing so might reduce the need to oversize the low-voltage >distribution infrastructure to accommodate the increase in Apparent >Power demand. That applies in some countries, where system impedances are high. For other, demographic. economic and social reasons, Ireland chose to upgrade its network, but other countries have not. But even in UK, where system impedances are generally quote low, the harmonics produce excessive currents in shunt capacitors and excessive voltages across series inductors, whether these are network or load equipment components. This raises reliability and even safety issues. In the 1950s, I witnessed two sub-station explosions, probably due to DC on the mains from TVs with half-wave rectifiers. These substations typically feed 500 residential customers. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk Things can always get better. But that's not the only option. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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.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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
