RFI Filters on VFD's on an IT Earthing System


Thread Starter

James Thomas

When using VFD's on an IT Earthing System (floating network) should RFI filters be used or not ?

If a 45 ohm resistor was connected between the transformer star point and ground to restrict fault currents would the above answer still apply ?

Hakan Ozevin

You cannot use RFI filters in a floating network, because the high-frequency disturbances should be transferred to the ground. Otherwise RFI filer will not work. Answer to your second question: no, because in such a case you are doing nothing but amplifying the disturbances. An RFI filter is a low pass filter which is sending (=shorting) the high frequency signals to the ground.

If you are using VSD in an very sensible location, then you must have a "grounded room".
You can contact to www.tesch.de who are experts on this subject. You can contact to me if you need further assistance.

Good luck

Hakan Ozevin