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vsd power factor instable


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#1 faycal

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Posted 06 April 2005 - 10:01 PM

we have 3 vsd , installed on 3 sea water lift pumps, 3.3kv
generators trip due to instable power frequency of 1 ,
which go to zero when we get two pumps onn line, the value is not stable at all
the vendor of vsd has recommended we get he capactitors closed when the pump strated and rump up, in order to limit the influence of the capacitors.
what are the capacitors affect on the power quality? and can the switching of the capacitors cause a transient and overvoltage that can cause the vsd inverter input damage?
do the trip could be the result of a phenomene of resonnance developped in the motor drive?

#2 marke

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Posted 07 April 2005 - 04:55 AM

Hello faycal
Welcome to the forum.

The power factor of vsds is typically well below 1 and is harmonic or distortion power factor as opposed to displacement power factor.
Many drive manufactures rate the cos phi as better than 0.95 implying that the power factor is better than 0.95, but the input rectifiers cause high harmonic currents to flow and this results in power factors typically between 0.5 and 0.9

Adding capacitors will not help improve the power factor when you have a distortion power factor. I would recommend that you try adding 3% or 5% reactors on the input of the vsds.

Harmonic currents can cause problems with the AVR on generator sets and I expect that this is the problem.

Best regards,




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