Thanks to all who replied to my earlier email.
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? Does a higher fundamental load make the affects of harmonic emissions less of a problem on a public low-voltage ac distribution system? Several replies have suggested we test the instrument in different current load modes. Here is the problem with 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. 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. 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. This is another topic I’m finding very interesting. Again, I’m a newbie and though I have read through the standards several times lacking the background and experience on this topic I’m sure there are huge gaps in my understanding. Thanks to all, The Other Brian ________________________________ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of ralph.mcdiar...@ca.schneider-electric.com Sent: Thursday, April 22, 2010 7:39 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Harmonic Emissions Testing Would it be sensible to test it in both transient (warm up) and in steady state operation? If the transient operating condition was brief (say < 5 minutes) then I would argue that it could be waived as a mode of operation needing 61000-3-2 evaluation. A minimum period of 'disturbance' likely needs to be defined. _______________________________________ _____________________________________________ Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | Compliance Engineer From: John Woodgate <j...@jmwa.demon.co.uk> To: EMC-PSTC@LISTSERV.IEEE.ORG List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: 04/22/2010 12:40 AM Subject: Re: [PSES] Harmonic Emissions Testing ________________________________ In message <0ed66cd2c9bd0a459d54fb9119a605670168d...@mailserver.lecotc.com>, dated Wed, 21 Apr 2010, "Kunde, Brian" <brian_ku...@lecotc.com> writes: >If an instrument could operate in different modes at different current >levels, what do you use as the Reference Fundamental Current in the >61000-3-12 test? The maximum Fundamental Current of the instrument in >any mode? > > > >In section 4.1a of the 61000-3-12 test, it says, ?During the >measurement of the reference fundamental current, the r.m.s. line >current shall be equal to the rated line current Iequ stated by the >manufacturer?. I?m not really sure what this means unless they are >saying it is measured when the device is drawing maximum current. This issue has already been raised and will be discussed at a meeting of the IEC committee next week. I cannot predict the outcome, but there is wide agreement that 'something must be done'. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK I should be disillusioned, but it's not worth the effort. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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