Thank you, Mr. Woodgate, I am sure many of the American contingent are grateful for your explanation.
taniagr...@msn.com ----- Original Message ----- From: John Woodgate Sent: Saturday, August 18, 2001 3:25 PM To: emc-p...@majordomo.ieee.org Subject: Re: CE test suite for computers I read in !emc-pstc that Tania Grant <taniagr...@msn.com> wrote (in <oe127msph2q6dqajy4k00004...@hotmail.com>) about 'CE test suite for computers', on Sat, 18 Aug 2001: > Most people will never understand anything unless it is explained > to them. Merely stating > that the power distribution in Europe and America is not the same, > is not an explanation but could even be construed as a lofty > put-down. I think one would have to be touchy to regard it as a put-down. I admit to some exasperation, in that members of IEC SC77A/WG1 and WG2, especially the US and Canadian experts, have been working hard to convince their professional colleagues that the European requirements on harmonic current and voltage-change emissions are *fairly* soundly- based, not inventions of the Devil. Had the European electricity supply industry been a little less secretive, and offered more comprehensive explanations for the need for emission control, much of the controversy of the last 10 years might have been avoided. > > If anyone out there can explain the difference between American and > European power distribution, and why harmonics are not such a big > problem in the U.S., I am sure that many of us will be extremely > grateful. Well, it isn't a big secret but it isn't common knowledge in the Americas. I feel sure that much more exhaustive explanations than that offered below can be found by a web search. Several US and Canada-based academics have written on the subject. Briefly, in the Americas, power is distributed at Medium Voltage to points very close to where it is used, and transformers of no more than a few tens of kVA rating deliver Low Voltage, 220 V centre-grounded, to residential and light industrial users. The transformer impedances are lower than is usual in Europe, even allowing for the voltage differences. The MV network impedances are also lower than in Europe. Because the supply impedances are lower, a given amount of harmonic current produces less voltage distortion, and that is what tends to cause adverse effects, except 'hot neutrals' due to triplen harmonic addition in the neutral conductors of 3-phase 4-wire systems. Because the supply impedances are lower, and fewer users are fed from each transformer, voltage-changes due to rapidly-varying load currents are smaller and affect fewer users. 120 V lamps have thicker filaments and flicker less for a given transient voltage change. All this is being studied and documented by the above-mentioned IEC WGs, and improved standards, and other types of publication, will result in due course. In Europe, up to typically 500 residential and light industrial users are supplied from one 500 kVA or larger transformer, so the LV cable runs are much longer than in the American system, and deliver nominally 230 V single- or 3-phase (230 V phase voltage), with wired neutral. The way that the neutral is grounded differs between European countries: France, UK and Norway use systems that are not like the US system, whereas other countries' systems are more similar. The MV network impedance is quite high (maybe over 15%), necessitated, AIUI, by fault- level requirements which I personally have not studied in detail. > > And can someone explain to me why the European Community is > adopting the American Energy Star Program? -- Albeit rendered in > their own language! > No-one knows why the EC does anything. (;-) -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co..uk Eat mink and be dreary! ------------------------------------------- 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
