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COS PHI


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#1 gogo

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Posted 31 May 2003 - 01:39 PM

Hello All,

I have an ABB drive ACH 400 series, one of the parameters is:
MOTOR COS PHI
nominal motor cos phi from the motor name plate range 0.50-0.99

Is this power factor? Can someone please explain? What effect does this have on drive? Motor?
Thanks!

#2 marke

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Posted 31 May 2003 - 09:07 PM

Hello gogo

Yes the cos phi of the motor is the power factor of the motor. This does not however affect the power factor on the input of the drive.

By definition, power factor is the ratio between KW and KVA. If the voltage and current are sinusoidal, the power factor is equal the the cosine of the angle between them (Cos phi). If the voltage and/or current and not sinusoidal, then the cos phi does not indicate the true power factor. This is particularly true of inverter drives where the input current is a series of pulses ocuring at the crest of the voltage waveform. This current is the current required to charge the DC bus capacitors. The conduction angle of these pulses will vary from very narrow with some drives to as wide as 120 degrees maximum, depending on the design of the inverter input stage and the impedence of the supply. In this case, as the current is in phase with the voltage, the cos phi is often correctly stated as better than 0.95, but the true power factor is usually less than 0.75 As this power factor is low due to harmonic currents, it can not be corrected by capacitors, and needs expensive filtering systems to make an improvement.

Best regards,

#3 GGOSS

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Posted 04 June 2003 - 12:28 AM

Hello gogo,

Some drives have a 'motor mapping' facility whilst others require the user to enter details of the motor via parameter setting. Although I cannot comment as to which of these applies to the drive you mention, in response to your question "what affect does this have on the drive" my best guess is basically nothing other than it enables the drive to control and protect the motor to the best of its ability.

Hope this helps.

Regards,
GGOSS




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