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Poor Power Factor due to harmonic current


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#1 Guest_song123_*

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Posted 04 March 2006 - 12:09 PM

Dear Friend,

My name is Anson and I am a new member for this forum.
I have read the latest Mark's reply regarding the previous discussion on The relationship between power factor and harmonics and I think it is really useful for me =)

It is said that poor power factor could be the result of harmonics current.
However (if I am not mistaken) I have read from a website that a poor power factor will make the supplier suffer loss. Therefore, an electricity customer can be charged higher by the supplier for the usage of low power factor electricity. Is it true ?

If yes, I would like to ask why there is still a lot of AC voltage phase control device, for example a lamp dimmer sell in the market nowadays ?

Of course this kind of dimmer is working as energy saving as the load will consume lower power.
However, in return this controller will make distortion at the current waveform and as a result the power factor will be degraded a lot. Especially if the lamp is dimming more than 50%. The power factor will be only 0.5.

Anyone of you can give some comment on this ?
Mark maybe ?

Thank you very much =)

#2 marke

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Posted 07 March 2006 - 09:59 PM

Hello Anson
Welcome to the forum.

A poor power factor can be the result of high harmonics and/or high reactive currents. The reactive currents can be reduced by the use of capacitors or inductors, but the harmonic currents require special active or passive filters and are very expensive.

A poor power factor increases the loading on the distribution system, transformers lines switchgear etc, but does not affect the KWHR usage. If the user pays on KWHr only, the poor power factor will not cost them unless they have significant distribution equipment between the driven load and the metering equipment.
Industrial users are often encouraged to have an improved power factor by adding penalties to their power bill. These penalties may be for KVA Max demand, poor power factor, KVAR demand etc. If there are penalties paid, then the customer is penalised, otherwise he/she is not.

Computors and flourescent lamps have high harmonic currents and would contribute far more to the supplier losses than light dimmers, but it all does add up.

There are some harmonic limitation regulations in some countries and I expect that these will gain more importance in the future.

Best regards,




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