Glenn, One answer is that one PC on its own can't be a problem, 200 PC's in different locations can in total have an effect on the supply system (and thus on other equipment connected to it - so with items in widespread use some individual product limit is needed) but with 200 PC's in a single location the total harmonic current drawn may be sufficient to cause serious site problems. Other examples we've been involved with include banks, trading floors, etc.
A good analogy would be with leakage current. Even if a single device meets the product spec, supplying a number of devices in parallel (e.g. thru a socket strip) might be sufficient to exceed safe limits and trip protective devices. So site-level harmonic mitigation is a neccessary intermediate step between control of individual items of equipment at one end and protection of the supply system at the other. I expect John Woodgate can explain this much better than me! Regards, Bill Lyons Claude Lyons Limited Claude Lyons Limited, Brook Road, Waltham Cross, Herts EN8 7LR, UK Tel: +44 (0)1992 768 888 email: b...@lyons.demon.co.uk Fax: +44 (0)1992 769 849 URL: http://www.claudelyons.co.uk -----Original Message----- From: "Lesmeister, Glenn" <glenn.lesmeis...@compaq.com> To: emc-p...@ieee.org Subject: RE: Harmonics List-Post: emc-pstc@listserv.ieee.org Date: Wed, 28 Feb 2001 14:06:15 -0600 There may be a lot more to the story, but it sounds like the HRT is doing a good job. It also sounds like the frequency converter was the culprit and not the 200 PC's (or whatever) that was also connected to the power system. Why should all equipment need harmonic control when only some equipment cause problems? Regards, Glenn Lesmeister Product Regulatory Compliance Compaq Computer Corp. Tel: 281-514-5163 20555 SH 249, MS60607 Fax: 281-514-8029 Houston, TX 77070-2698 Pgr: 713-786-4930 glenn.lesmeis...@compaq.com "I am empowered to do what makes sense!" -----Original Message----- From: m...@cjbdev.demon.co.uk [mailto:m...@cjbdev.demon.co.uk] Sent: Wednesday, February 28, 2001 11:48 AM To: emc-p...@ieee.org Subject: RE: Harmonics This month's Electrical Review (a free trade magazine in the UK) has just fallen on my desk, with this text and its associated picture taking up about a fifth of the area of the front page - I'm quoting it just for interest with regard to this thread! "Perfect Harmony? Power conditioning equipment specialist Claude Lyons has installed a 200A harmonic rejection transformer at RAF Lakenheath to reduce the problems caused by harmonic currents. The recent installation of a frequency converter had caused harmonic distortion on the low-voltage network. Cables were overheating and equipment was failing. The HRT was specified to redirect the harmful currents. After installation, Claude Lyon monitored the unit and found a reduction in the production of harmonic currents - from 72 to 19A in the main neutral cable." Regards, Mark PS Disclaimer: any copyright breaches are my fault (in my ignorance) and not those of my employer. -- Mark Hone Wellman CJB Limited Email: m...@cjbdev.demon.co.uk Airport Service Road Tel: +44 (0)2392 629239 (Direct) Portsmouth, Hampshire Tel: +44 (0)2392 664911 PO3 5PG, ENGLAND Fax: +44 (0)2392 697864 ------------------------------------------- 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: http://www.rcic.com/ click on "Virtual Conference Hall,"
