I'd like to second Pete's comments. In the rush to get power factor correction (PFC) circuits we replaced out of phase power with even lossyer in-phase power with EMI problems as well. PFC makes the situation worse when it is combined with other non PFC SMPS because it tries to correct for the non PFC SMPS.
Also sometimes forgotten is the fact the PFCs can cause neutral currents greater than line current in 3 phase SMPS. No good deed goes unpunished. Fred Townsend DC to Light Pete Perkins wrote: >PSNetters, > > To repeat an old quotation: Those that don't know their history are >bound to repeat it. > > The introduction of SMPS into electronic equipment in large numbers >led to unexpected problems in electrical installations. > > The key technical problem initially identified was the development >of harmonics which were not properly accounted for in the installations. > > One issue was triplen harmonics (especially 3rd, but includes 9th, >15th etc) which were fed back into the delta primary of distribution >transformers where they circulated and produced heat. This caused large >transformers to overheat and burn up unexpectedly, to the chagrin of >utilities and industrial & commercial customers who had not understood what >they were getting into when they purchased large numbers of computer >terminals and, later, computers and other electronic equipment. > > In the early '90s I participated in an ongoing UofWisc/CBEMA >sponsored seminar on 'Effects of Non-linear Loads on the Power Distribution >System' presented a number of times in the US. We presented some clipped AC >voltage waveforms commonly found in our industrial buildings as part of this >discussion. The purpose of the day-long 2 dozen paper presentation was to >get facilities engineers apprised as to this developing problem and provide >some guidance in sizing their system to properly handle this non-linear >load. A common experience was that only about 1/3 of the expected load >could be connected in the facility before these problems developed. > > From my recollection, the Euro drive for a standards based fix was >driven by the British experience. From what we heard, at the beginning of >the Falkland's war, when it was announced that Queen Elizabeth would speak >during the dinner hour that the troops were going to protect the peace >everyone had hurried home and turned on their Sony TVs to get the >announcement. The large transformers that serve 600 or more residences each >in the apartments in London developed the primary triplen harmonics >overheating mentioned above and a number of them burned out leaving large >groups of folks without power until the transformer could be replaced. > > Americans, as John Woodgate continues to remind us, are smarter than >that and have left the solution to the private market. > > From my point of view another unexpected consequence from this >technology has been the development of non-sinusoidal Touch Current from the >use of these SMPS. The addition of Power Factor Correction has only served >to make the problem worse and now the further addition of another switcher >to get to the high efficiency and low power sleep modes will only make this >worse. > > To see some TC waveforms go to Art Michaels site: www.safetylink.com >and search on my name Perkins and you will find a couple of dozen TC >waveforms along with their respective input current waveforms. These have >been taken from many different products as a part of my safety & regulatory >consulting business over the last 12 -15 years. From this I have given a >number of papers at the IEEE PSES on TC issues showing the need to move to >peak TC measurements of these waveforms because of this unexpected >complexity that has developed from all of this. > > The increasing use of switching electronics in consumer products >(both electronic and motor driven) will further acerbate this problem. > > Another American quote (attributed to Patrick Henry, a founding >father): Eternal vigilance is the price of freedom. > > So, be alert, the world needs more lerts. > >br, Pete > > Peter E Perkins, PE > Principal Product Safety & Regulatory Consultant > Tigard, ORe 97281-3427 > > 503/452-1201 fone/fax > [email protected] > >- >---------------------------------------------------------------- >This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> > >All emc-pstc postings are archived and searchable on the web at: >http://www.ieeecommunities.org/emc-pstc >Graphics (in well-used formats), large files, etc. can be posted to that URL. > >Website: http://www.ieee-pses.org/ >Instructions: http://listserv.ieee.org/request/user-guide.html >List rules: http://www.ieee-pses.org/listrules.html > >For help, send mail to the list administrators: >Scott Douglas <[email protected]> >Mike Cantwell <[email protected]> > >For policy questions, send mail to: >Jim Bacher: <[email protected]> >David Heald: <[email protected]> > > > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
