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Do Harmonics Cause Dissonance?

Posted December 01, 2011 9:19 AM

A recent article in Design Engineer describes the impact of harmonic distortion (created when using AC drives) can have on power supplies. Have you experienced this problem, and if so, how did you handle it?

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Tornado
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#1

Re: Do Harmonics Cause Dissonance?

12/02/2011 3:55 AM

Either that or cacophony.

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Andy Germany
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#2

Re: Do Harmonics Cause Dissonance?

12/02/2011 11:44 AM

I'm not sure whether this truly deserves to be here, but I have friends who have made their own CNC machines, but with relatively simple linear or worse unregulated power supplies with no voltage control at all. They usually end up gaining or losing steps on the stepper motors.....

People who build HUGE linear supplies, with say more than 3 x the max current ever needed (but they can make toast on the cooling fins), tend to not have quite such problems.....except with the electricity bill!!

I personally promote the usage of switched Mode Power Supplies (against many who believe it to be a waste of resources!) and have been able to help a few out with my home built supplies (from an Elektor design in 2003) which run cool and at around 86% efficiency....it was originally designed for a very Hi Fi amp and reacts well to sudden load changes, its short circuit and over heating proof.

Its not to do with VFDs, but it is to do with strange resonances on the power when driving motors, but marking as off topic anyway before someone attempts to jump down my throat!!

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kvsubramanyam
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#3

Re: Do Harmonics Cause Dissonance?

12/02/2011 11:07 PM

The article addressed the problem correctly. I worked in a Lead Acid Battery manufacturing company for 7 years. There were many problems due harmonics generated by 6000+ battery chargers cum regenerative dis-chargers. ITHD 38% & VTHD 8% 5th & 7th harmonics predominant. First effect is that power factor capacitors will fail. Single phase preventors and phase sequence detectors do not work. Small motors may burn; mains transformer may heat up even at 50% load; Standby DG set may not take more than 50% load; so many. There are several techniques to handle this problem effectively but the solutions are industry/ situation dependent; hence can not be answered in just one sentence. I could handle harmonics very effectively. More than anything the top management MUST understand effects of un-wanted harmonics effect.

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Wal
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#4

Re: Do Harmonics Cause Dissonance?

12/03/2011 2:17 AM

One approach to harmonic suppression is mechanical filtering.

The noise (transients, harmonics, bog PF...) source is electrically isolated from intolerant loads through a flywheel on a motor alternator setup. AKA a series motor generator. Here is an example http://www.pscpower.com/pages/industrial%20motor%20generator.htm

I encountered this arrangement at an ESA tracking station where the variable speed slew motors exhibited particularly aggressive transient characteristics.

The noise stopped at the flywheel.

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