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PF Correction and VSD,s


Les L

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Hello Les L

 

If you are converting existing installations form direct connected motors to VSD connected motors, then the required power factor correction will certainly reduce. This does not mean the the power factor will improve, just that you can not power factor correct a motor on a VSD, and you can not power factor correct a VSD.

A VSD has a poor power factor due to high levels of harmonic currents on the input of the VSD. These can not be easily eliminated. Certainly, the addition of capacitors will not correct them. Additionally, the high harmonics produced by the VSDs will increase the current and heating on existing power factor corection capacitors used for other motors. You may need to use detuning capacitors with these capacitors to reduce the damaging harmonic current flow.

 

Bottom line, the used of VSDs will reduce the number of capacitors required for corection, but will not improve the power factor. The use of VSDs will also reduce the life of existing capacitors unless detuning inductors are used with the capacitors.

Best regards,

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