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BigMax

Member Since 28 Jun 2002
Offline Last Active Jan 29 2009 06:19 AM
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Posts I've Made

In Topic: Sine Wave Filters Have Limitations.

29 January 2009 - 06:18 AM

Hello Marke,

I've had some experience with a similar problem blink.gif

I agree that a sinewave filter can do a good job on differential mode energy... keeps the motor happy and reduces the effect of Voltage magnification with long cables.

BUT, I also noted that common mode energy (coupled to earth via motor cable capacitance) can still be considerable when sinewave filters are used.

The approach I took was to consider where this common mode energy was going to... there must be a 'circuit' of course... and as you have experienced Voltage distortion at the distribution level (causing load failures) it seems clear that a lot of the common mode energy is returning at the 'point of common coupling'.. i.e at the MEN point ohmy.gif ... then completing the circuit back to the VSD via its' mains supply.

What can be done?

I considered the common mode action of a typical EMC filter. To my way of thinking ™, the VSD input EMC filter (should) provide a low impedance return path for the common mode energy... with the bulk of this energy returning via the VSD local EMC filter rather than at the PCC / MEN point.

What I did simply was to take aditional (otherwise suitably rated) EMC filter(s) and added them to the input(s) of the of the VSDs (which had otherwise integral EMC Filters). Result? Much reduced THVD at the PCC laugh.gif

I hope this is helpful.

Cheers!

BigMax