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Harmonics


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#1 jamesdean

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Posted 25 January 2008 - 04:34 PM

Hello

can anyone shed some light on how to calculate harmonic voltage distortion

I have two 15kW VSD motors to be fed from a REC supply, 3 phase, 415V and require the harmonic voltage distortion this will cause.

cheers james

#2 marke

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Posted 25 January 2008 - 07:34 PM

Hello James

Welcome to the forum.

The harmonics produced are a function of the inverter design with particular improtance to the design around the rectifier stage. Some drives use a three phase rectifier straight into a capacitor bank and the conduction angle is very small resulting in a very broad band of harmonic currents. Others use a DC bus choke to lengthen the conduction angle and this reduces the harmonic currents and also eliminates the higher order harmonics.
Some use AC line reactors and this has a similar effect to the DC bus choke.

You need to talk to the VFD supplier to get some information on the harmonic currents for the particular drives that you are using.
Once you know what the harmonic currents are, you can calculate the harmonic voltages at each harmonic from the harmonic current times the supply impedance at that frequency.

Best regards,




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