In message <0ed66cd2c9bd0a459d54fb9119a605670168d...@mailserver.lecotc.com>, "Kunde, Brian" <brian_ku...@lecotc.com> writes
>It would help me understand the intent of the harmonic standards if I >knew what the goal of these standards were. Are they to limit the >actual harmonic current or only the harmonic current in reference to >the overall load? No: the goal is to limit *voltage distortion*. But there are BIG problems with measuring voltage distortion for individual products, so current is measured. >Does a higher fundamental load make the affects of harmonic emissions >less of a problem on a public low-voltage ac distribution system? > Yes, because voltage distortion is reduced. >Several replies have suggested we test the instrument in different >current load modes. Here is the problem with that. > The main problem is that the standard does not allow you to do that! > > >Let's say we have an instrument that under full load draws 2 amps at >the 3rd harmonic and 25 amps at the fundamental. 2 amps is only 8% of >the fundamental, which is passing the 61000-3-12 test (table 2 limit is >21.6% at the 3rd harmonic). In a different mode of operation, the >instrument again draws 2 amps at the 3rd harmonic but the fundamental >is only 5 amps, which is 40% and would Fail the 61000-3-12 test, yet >the harmonic current is exactly the same in both modes. Another >strange thing is that in this mode of operation it would pass the Class >A limits of the 61000-3-2 test which is 2.3 amps at the 3rd harmonic. The committee is well aware that anomalies, real and apparent, can arise. It continues to try to deal with them as they are reported. Instant solutions are rare. > >In the above example, we can claim compliance with the 61000-3-12 test >IF we declare a Short Circuit Ratio of 350. This translates into >requiring a very low system impedance which seems strange to me that it >would be required only in a mode where the instrument is drawing little >overall current. > Yes, an anomaly. > >Another question is how common are the terms Short Circuit Ratio and >Short Circuit Power to the people in Europe? If we put such a >statement in our documentation is anyone going to know what this means >and know what to do about it? A short Circuit Ratio of 350 on a 230VAC >system would have a Short Circuit Power of something like 7 megawatts. >I asked an electrician here in the US if our mains system can handle >this and he started to hyperventilate. Obviously his wasn't familiar >with the terms. The terms are well-known to supply-system people and designers of large equipment. It is true that others need to learn about them, but that applies to very many terms used in EMC. -- This is my travelling signature, adding no superfluous mass. John M Woodgate - 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 <emc-p...@ieee.org> 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 <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
