I read in !emc-pstc that Ken Javor <ken.ja...@emccompliance.com> wrote (in <0h9j008afer...@mtaout03.icomcast.net>) about 'Unity Power Factor' on Thu, 30 Jan 2003: >Yes I am in the US so clearly I must have been mistaken. Seriously, when >that business started in 1989 there were relatively few PCs in use there. >"PC cubes" were scattered throughout the building that people could use on >an as-needed basis. By 1995, every engineer's cube had a PC running all day >long.
Yes, a similar thing happened in Europe. It was this *rapid* expansion of PC deployment that frightened the European electricity suppliers. They coped earlier with the far more gradual development of the TV park, first persuading the TV manufacturers to give up half-wave rectifiers and subsequently to control the harmonic emissions of very large sets. They extrapolated the effects of the rapid expansion of PCs (and simultaneous use of more than one TV per household) and deduced that widespread system failures would occur in a few (5?) years (counting >from about 1989) if the emissions remained controlled only by the Class A limits of IEC/EN60555-2. Hence the invention of 'Class D' and all the ensuing grief. It has now been shown pretty convincingly that the extrapolations were very pessimistic. The latest European supply industry predictions, based on voltage distortion growth levels of the past decade of 0.1% absolute per year (by 'absolute', I mean a growth from, say, 4% to 4.1% at a a particular site, not from 4% to 100.1% of 4%!), is that unacceptable levels of supply disturbance will occur in 10 years time. However, there are several reasons why that 0.1% growth rate will not be maintained over that time period, not least the effect of IEC/EN 61000-3-2 itself, which will not be reliably measurable, in Europe, until 2005 at the earliest. > It would have been interesting, in retrospect, to have taken line >voltage oscillographs at representative locations as the PC density >increased. Yes, it would have. I have about a 20 year gap in observations of the mains waveform here in UK, from about 1971 to 1991, when I heard about Class D and started to study the subject closely. During that time, the flat tops developed. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
