I read in !emc-pstc that [email protected] wrote (in <3d.180a271a.297 [email protected]>) about 'EN 61000-3-3 compliant heater controller', on Wed, 23 Jan 2002:
> Mathieu van den Bergh is not just any ordinary old consultant, he is a > member of the TC77/SC77A Working Group that is responsible for IEC > 61000-3-2 > and appears to have a great deal of experience and knowledge in the area > of > harmonics. That is true, but his views are not necessarily shared by other members of the WG, some of whom are equally expert. > > He is also based in the US, where most of the 'denial' of harmonics > problems > seems to arise, despite well-known problems with harmonics in the USA. I think we are getting close to an invasion of privacy here; the country of residence of Mathieu or anyone else is not relevant to any technical argument. > [snip] > > Since he appears to be an expert in these matters, I hope you will not > mind > me quoting a little more from his August 19 2000 reply to Conformity > Update: > > "A number of studies in countries including Switzerland, the UK, France, > Scandinavian countries, Japan, and the USA, have shown that harmonic > distortion has increased from about 2 - 2.5% in the late 70's - early 80's > to about 4 - 4.5% in the mid-late 90's with distortion in heavily > industrialised areas reaching 6 - 7%!! Those last figures are probably true, but are not the whole truth. Electricity suppliers can, if they wish, and very often do, accept by special contract the connection of large non-linear loads which, *on their dedicated supply* result in high levels of voltage distortion. > It has also been proven through many studies and observations that > harmonics > related problems increase significantly when distortion levels exceed 5% > and > that they become very serious and costly when distortion approaches 10%. Indeed. Below 10%, in fact. Problems start to show up if 8% is closely approached. > It > has been generally accepted therefore that distortion is increasing at 0.1 > - > 0.15% per year in industrialized nations. While that is again, possibly true, the word 'therefore' seems unjustified. The point here is that voltage distortion on the **public low-voltage supply** (which is what IEC/EN61000-3-2 is about) varies from place to place and time to time, over a range of perhaps 2% to near 6%. So any 'rate of rise' depends rather a lot on when and where the raw data were collected. Furthermore, the uncertainty associated with a rise of 0.1% per annum almost certainly embraces zero and may even extend into negative values. The reason is that while the *number* of non- linear loads connected is, beyond reasonable doubt, increasing, the *power* per load is decreasing. For example, there is concern in some quarters that even certain very large TV sets now have a power consumption of less than 75 W and thus are not subject to limits in IEC/EN61000-3-2. > If no action is taken it is to be expected that distortion levels will > start > to exceed critical levels within a few years." We heard that in 1991, and I believe it had been stated several times before that. We hear it again at almost every meeting of the WG. The 'day of reckoning' seems always 5 years or so away, probably because of the compensating effect of reducing power consumption. > > Notice Mr van den Bergh is referring here to waveform distortion, not > neutral currents or zero-phase flux in transformers, both of which are > problems only for individual sites not the distribution network as a > whole. > He goes on... > > "The proliferation of electronic equipment with switch mode supplies falls > in the same category as the lighting related problems about 20 years ago." > > I agree with you that the harmonics problem can be ameliorated by actions > taken at the power distribution network level, This can be done to some extent. It's not very practicable when the harmonic content varies rather rapidly. >or by actions at the load > level, but I have not investigated their relative economic cases. Evidence has been presented that the *annual* cost of harmonic mitigation ONLY at product level is of the same order as the capital cost of mitigation ONLY at supply system level, which would clearly involve equipment having a lifetime much longer than one year. But passive mitigation only at system level has the disadvantage of not reacting (!) to rapid changes, while active mitigation at system level is still experimental. Furthermore, governmental approval for investment in system level mitigation is unlikely in many European countries. Unfortunately, elements in the European supply industry are opposed to mitigation at *site* level, which for light industry is an attractive proposition. The reasons for the opposition are unconvincing, to say the least. It is almost axiomatic that the best overall economic solution (least total cost to the end-user) is the informed use of ALL technical solutions - mitigation at equipment, site and system level. > > But whichever method is adopted, the customer pays the bill eventually and > I > have more confidence in the highly competitive world of electronic > products > to come up with a cost-effective solution in a timely manner. > > I have some knowledge of power-factor correction techniques in switch-mode > supplies, and some of them can cost very little indeed. So I really don't > know why the US computer industry is making such a fuss about controlling > harmonic emissions. Because it thinks it can get more relaxed limits in the second edition of IEC/EN61000-3-2 by continuing to insist that the present limits were imposed with insufficient, if any, technical justification. > > [snip] > > > I suspect the real reason for the computer industry's denial of harmonics > problems, or else blaming them on a poor distribution system, is that US > computer manufacturers simply want to make one model they can sell > world-wide so they want whatever is permitted in their main market (the > US) > to be permitted everywhere else. They don't SELL the same models everywhere because if they did it would be obvious how much more gross margin they make in Europe than in USA. Comparing like-with-nearly-like, the exchange rate for ITE and much other stuff is USD1 = GBP1. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. 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