Rick: Sounds like the harmonics are adding or canceling as the case may be. Check to see if the offending harmonics are triplen or other harmonics. The high harmonics are sometimes tricky in the way they behave. Harmonics are always a function of the AC supply impedance. I would suspect investigate the supply impedances and compare them with the type of harmonic behavior. Would be happy to discuss.
Dave George Ergonomics, Inc. 215 357 5124 From: <rbus...@es.com> To: <emc-p...@ieee.org> Sent: Thursday, February 20, 2003 3:58 PM Subject: Harmonics Testing for PCs > > > Recently I had the opportunity to test one of our latest products, which > has essentially 6 rack mounted PCs and a custom designed graphics > processor. The graphics processor has two internal (identical) power > supplies on separate power cords but with a shared output current. The > purpose of the dual cord is to balance the input current across the > three phases. All power supplies are PFC. The system is three phase with > all cords connected phase to natural (120V or 230V) by way of a power > distribution system. > > During the Harmonics test (EN 61000-3-2) the system failed harmonics. > Testing all of the peripherals individually, they all passed. As a > system, the only way it would pass is to have both power cords from the > graphics processor plugged into a single phase. Obviously this > compromises our ability to balance the input current as well as we would > have liked. > > So my question to the group is: > > 1. Why would the arrangement of the power cords affect the harmonic > noise. My guess might be a defective power controller but beyond that I > am perplexed. > > On a similar note, another similar system was tested to EFT and Surge > per EN 61000-4-4 and EN 61000-4-5. During the testing one of the six > power supplies popped at 500V. It sounded a lot like an MOV exploding. > Contacting the manufacturer he provided me extensive test data and an > assurance that the supplies are designed to pass the test. I am now in > the process of re-testing. My question is: > > 2. What is the effect of EFT or Surge on a system as opposed to a > individual chassis or p/s. It seems to me that the more power supplies > on a given input, the greater the chance that the energy would be > absorbed and the system passing. > > Thanks > > Rick Busche > Evans & Sutherland > rbus...@es.com > > > ------------------------------------------- > 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: > Ron Pickard: emc-p...@hypercom.com > Dave Heald: davehe...@attbi.com > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > > 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
