EMI from a VFD
EMI from a VFD
(OP)
I am using a 1/2HP motor controlled by a VFD to rotate an electronics package ~2 ft away as part of a testing fixture. The motor is fixed to an aluminum plate as is the fixture for rotating the electronics package. For *some* of my packages I am getting garbled output when the drive is engaged (but fine when it is off). When the package is moved to ~4 ft away there is no problem. I am suspecting EMI from the drive as the cause of the problem, but I would like to not have to re-build the base of my fixture and drive to create the increased separation. Is there any simple way to shield my electronics from the EMI to avoid the signal problems?
I do not know the frequency of the EMI (if that is indeed the problem).
Thanks for any help.
I do not know the frequency of the EMI (if that is indeed the problem).
Thanks for any help.





RE: EMI from a VFD
VFD enclosure should well grounded and could be enclosed in a metal enclosure if possible.
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RE: EMI from a VFD
Also, keeping the VFD in an HF tight box which shall be bonded to the test rig with short and wide straps is good. It will reduce air-borne emission.
Gunnar Englund
www.gke.org
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RE: EMI from a VFD
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RE: EMI from a VFD
RE: EMI from a VFD
The problem is due to high frequency noise that is capacitively coupled from the motor windings to the frame of the motor. You need to provide a very low impedance return path for that noise from the frame of the motor to the frame of the VFD. This requires surface area on the return earth path rather than cross sectional area and this is best achieved by the use of a screened cable with the screen well bonded both at the motor end and the VFD end.
The screen termination should be in the form of a clamp or gland that connects all the way around the screen. Do not use pigtails as you have then reduced the surface area and created a constriction.
If the noise level is still too high, the next step is to fit an EMC filter on the input AC supply right at the VFD input. A ferrite ring on the output three phase (but not the screen) may help also.
Best regards,
Mark.
Mark Empson
L M Photonics Ltd