Motor Drives and Power Factor Correction.

Just curious if anyone has heard if pfc has been applied to small motor drives (or even computers). I would imagine the european regulators will be pushing pfc as they love to impose rules. So down the road USA manufacturers will be forced to provide pfc.

A possible benifit would be a manufacturer could potentially produce one particular hp drive and use different pfc front end units.

example: produce a 1hp 230v 3 phase drive which would be the standard. If customer wants single phase operation sell him a pfc. If a customer wants to run 230v motor off of 120vac sell him a pfc. Maybe same pfc could be used for both applications - If not we're back to producing three units, a drive and two pfc.

regards, Bob

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There's no reason to do pfc to small installations.(I.e.normal households).Large installations need them, because they pay fines if their power factor (cos phi)is too bad, usually below 0.85 inductive.They have kVArh energy meters.(kilo Volt Ampere reactive*hour).Reactive power (I don't know if that's the right term in english-Blindleistung in german)is V*I*sin phi, where phi is the angle between voltage and current.The utility wants large cosumers to improve their pf, because generators, transmission lines, transformers and distribution lines need be constructed larger, in order to carry the larger currents needed to oscillate energy between alternator and load, the alternator playing the role of a capacitor and the load of an inductor.So, the factory (usually)has to install its own capacitors, which are energized automatically as more iductive loads come on line.

-- Dimitris Tzortzakakis,Greece Visit our website-now with aircondition!

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Tzortzakakis Dimitrios

Yes I agree with what you say concerning phase angles and penalties charged for poor power factor.

Capacitor input drives as well as computers pull large harmonic currents. In fact I have run simulations where the harmonic current distortion is greater than 100% on stiff power lines with large inverters. More transmission losses in this case sending harmonic currents down the line than actual usable power. I would imagine small systems like residential power not affected as much as these are generally soft lines with mushy transformers etc.

From a manufacturers point of view it may actually be cheeper to produce a drive with pfc than without. As an example I work for a drive manufacturer which makes 115v doubler units. Very nasty harmonics and large filter banks to reduce the ripple voltage. I could take a 230v unit and add pfc and pull nice sinewaves off of power line for similar money that I spend for large filter caps. Similar relationship between single phase and three phase. Maybe sizes like 5-10 kw at 220v single phase 50Hz would be a good place to begin looking at pfc.

From the point of view of regulating agencies I have not a clue. Based on history i would say before too long they will be doing what they do best and drive manufacturers will be putting pfc in smaller sized units.

In any case I have small pfc set up on drive front end that I will play with. Just wondering if it's time yet to begin looking at marketing applications.

Thanks for response.

Regards, Bob

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There is already IEEE 519-1992 which sets maximum permissible current distortion limits of about 5% to 20% THD(5% for small drives & getting progressively lenient where largest drives are allowed upto 20% THD).

Reply to
Nam Paik

IEEE 519-1992 sets limits at the point of common coupling (service entrance). It does NOT apply to individual pieces of equipment.

Charles Perry P.E.

Reply to
Charles Perry



IEEE 519 also specifies TDD not THD. That's Total DEMAND Distortion. At 1/2 load the THD can be twice as high, 1/3 load three times as high etc.. The limits (5% TDD, 10% TDD or 20% TDD) are also based upon the source impedance (measured on a per unit basis) not the size of the load.

Individual pieces of equipment often specify 5% THD as "519 compliant" because if all of the loads have 5% THD, then the installation will meet IEEE519. It is extremely rare on the other hand, to actually need even the large loads to have 5% THD to meet 5% TDD at the service.


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Matthew Beasley

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