I read in !emc-pstc that Rich Nute <ri...@sdd.hp.com> wrote (in <200201232003.maa21...@epgc264.sdd.hp.com>) about 'Harmonic current emissions', on Wed, 23 Jan 2002: > > > > >Hi Keith and Ghery: > > >There are a number of effects of harmonic current >emission from non-linear loads. > >1) When a large number of loads rich in triplen > harmonics are supplied from a 3-phase source, > the neutral current can be as high as root 3 > of the phase current. (This effect does not > exist on a single-phase distribution system, > or on a 3-phase system where each phase has > its own neutral.)
Consider that the 3rd harmonic current of a high-efficiency single-phase rectifier is near 90% of the fundamental. Then consider that the third harmonic currents *add arithmetically* in the neutral. That give a neutral current of 2.7 times the fundamental current. If you take all the triplen harmonics into account you get a neutral current of 2.85.. times the fundamental current in one phase. > [snip] > >The USA computer industry has been quite forward in >addressing effects 1 and 2. The computer industry >was the force behind a series of academia-based >seminars on the causes and solutions to effects 1 >and 2 that resulted in changes to the USA National >Electrical Code and to distribution transformer >testing and ratings. (I presented in some of those >seminars.) > >This is NOT denial. > >> 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. > >One of the USA's major objections to EN61003-2 is >that remedying the load repeats with each new product >that is introduced, while remedying the source is a >one-time remedy. EN61000-3-2 requires continous >cost to the consumer with each product. (The cost >is NOT trivial -- nearly double the cost of the power >supply.) No, that's certainly an exaggeration. We have been told various sums from USD1 to USD5, and I suspect that the lower value is nearer the truth. > Indeed, this has forced manufacturers to >develop one supply for the EU, and one supply for the >remainder of the world. And, forced two products for >the world instead of one. > >(One of the benefits of EN61000-3-2 has been a real >effort at power reduction so that more and more >products are below the 50-watt exemption limit.) 75 W. A change to 50 W would need a new vote by national standards committees, as is clarified in the Millennium Amendment. > [snip] -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. 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: 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: No longer online until our new server is brought online and the old messages are imported into the new server.
