Dear Ghery I am well aware of the undersized neutral problem, but given that we have a legacy of buildings with undersized neutrals it is not a simple or low-cost solution to uprate all their neutrals.
Anyway, harmonics in the mains distribution cause many more problems than simply overheating neutrals – waveform distortion is a greater worry. Since your negative approach to the need for harmonics control was similar to views expressed in an article in Conformity Update 08-06-00, I originally quoted from Mr van den Bergh's reply to that article. 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. 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 would have assumed that since you are knowledgeable in the field of harmonics you would already know Mr Van den Bergh and would already have discussed your concerns with him and (hopefully) come to some kind of agreement. 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%!! 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%. It has been generally accepted therefore that distortion is increasing at 0.1 - 0.15% per year in industrialized nations. If no action is taken it is to be expected that distortion levels will start to exceed critical levels within a few years." 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, or by actions at the load level, but I have not investigated their relative economic cases. 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. It reminds me of the fuss the auto industry made about compulsory seat belts, catalytic converters, etc., or the fuss the VDU monitor industry made about meeting MPR2 – all those things that were stridently opposed by manufacturers as needless added expense, or even impossible – yet we now find them in all the products we buy even though they still cost less in real terms than they did before. 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. Would you agree with this? Regards, Keith Armstrong In a message dated 22/01/02 17:34:47 GMT Standard Time, ghery.pet...@intel.com writes: > Subj:RE: EN 61000-3-3 compliant heater controller > Date:22/01/02 17:34:47 GMT Standard Time > From: ghery.pet...@intel.com (Pettit, Ghery) > Sender: owner-emc-p...@majordomo.ieee.org > Reply-to: <A HREF="mailto:ghery.pet...@intel.com";>ghery.pet...@intel.com</A> > (Pettit, Ghery) > To: cherryclo...@aol.com ('cherryclo...@aol.com'), > ghery.pet...@intel.com (Pettit, Ghery) > CC: emc-p...@majordomo.ieee.org > > Keith, > > Many times the neutral cable problems result from using a smaller gauge > wire for the neutral in the mistaken assumption that the neutral doesn't > carry any significant current (true if the 3 phase load is balanced - when > did you last see that?). Harmonics may make that problem worse, but the > fundamental frequency current can be a problem, as well. The solution, > used by many building designers, is to use the same size wire for the > neutral as for the phase conductors. > > Do you expect me to believe that personal computers cause significant > harmonics problems? There is no evidence of this in the U.S. If there is > in Europe, then you are admitting that your power distribution system > design is deficient. Lousy design on the part of the power providers is > fixed by saddling the manufacturers of the load with the full expense of > the solution? Sorry. I don't buy that approach. A facilities solution is > usually more economical than fixing the 'problem' at each individual load. > > Quoting a few consultants is nice, but doesn't prove a case. I remain a > total skeptic on this matter. IEC 61000-3-2 needs (and is getting) a > complete overhaul. IEC 61000-3-3 should be withdrawn. Flicker is real, no > doubt, but this issue gets more attention than it deserves in the home > environment. > > Ghery Pettit > > -----Original Message----- > From: cherryclo...@aol.com [mailto:cherryclo...@aol.com] > Sent: Tuesday, January 22, 2002 2:23 AM > To: ghery.pet...@intel.com > Cc: emc-p...@majordomo.ieee.org > Subject: Re: EN 61000-3-3 compliant heater controller > > > Dear Ghery > There is plenty of evidence, for harmonic problems, especially in large > cities and large office buildings. > > For example, an electricity supply engineer told me that in the financial > district in London there are buildings where they cannot fit any power > factor correction capacitors to the fluorescent luminaires - because they > fail within days due to the waveform distortion caused by harmonic > currents. > So they have buildings drawing 100's of kA of lighting current at a low > power factor (< 0.6 I understand). I also understand they have overheating > problems with cables under the Thames connecting the two halves of London, > due to harmonic currents. > > In the early 90's I spoke with a USA-based consultant who told me about a > number of problems (e.g. completely burnt-out neutral cables) he had seen > in buildings in the US where they had installed lots of single-phase > equipment. > > 'Banana Skin' No. 102 in the EMC + Compliance journal, Oct 2000 (read it in > the archives at www.compliance-club.com) describes harmonic overheating > problems with low-voltage lighting installations in hotels and public > buildings that has Fane Murray, a lighting consultant in the UK, very > concerned indeed. > > I understand that the power distribution in the USA is generally less > susceptible to waveform distortion than in Europe, nevertheless I > understand that the US has its own harmonics problems – Mathieu van den > Bergh, of Computer and Networking Services Inc., California said in August > 2000: > > a) for many years the US has had IEEE-Std-519 which has recommendations > for harmonic limits which are not much different from IEC 61000-3-2; > > b) the US lighting industry has voluntarily implemented ANSI harmonics > standards for fluorescent lamp ballasts that are more stringent than IEC > 61000-3-2, as the direct result of serious harmonics problems in large > office buildings; > > c) the US Government has issued several large scale procurement > requisitions for Information Technology that included far more stringent > harmonics requirements than those in IEC 61000-3-2. > > Time does not permit me to go through my files to provide a longer list of > real-life problems with harmonics. > > Regards, Keith Armstrong > R>In a message dated 21/01/02 23:54:36 GMT Standard Time, > ghery.pet...@intel.com writes: > > >> Subj:RE: EN 61000-3-3 compliant heater controller >> Date:21/01/02 23:54:36 GMT Standard Time >> From: ghery.pet...@intel.com (Pettit, Ghery) >> Sender: owner-emc-p...@majordomo.ieee.org >> Reply-to: <A HREF="mailto:ghery.pet...@intel.com";>ghery.pet...@intel.com</A> >> (Pettit, Ghery) >> To: j...@jmwa.demon.co.uk ('John Woodgate'), emc-p...@majordomo.ieee.org >> >> So rather than educating the public on the cause of flicker, we get >> saddled >> with a useless design requirement. Typical bureaucracy - don't fix the >> problem, make it LOOK like you're doing something, at someone else's >> expense. Just like the harmonics standard - fix a problem that doesn't >> exist. >> >> >
