Protecting other systems from VFD's

[robertjo24]

I was hoping someone could put me on to some good information regarding protecting other systems (communications, video, etc) from the EMI generated by VFD’s.

Here is the issue…
We have several locations where we will have small (12X14) building that houses motor switchgear and controls equipment (PLC’s, HMI computers, etc), as well as other equipment like CCTV camera encoders. We also will have some network devices in the same building. All the motor switch gear and VFD’s are on one side of the building and all the controls and network equipment is on the other. There are cable trays existing the building, but often times they are common trays with separators in the middle. We have some locations that cause network disruptions and distortion in the video when the drives fire up.
The electrical group swears the drives, cables, and panels are installed per manufacturer’s spec and that they have install shielding, filters, and the proper ground bonding to eliminate the EMI.

I would appreciate any info that would help me to better protect the comms systems from the noise the drives produce.

 

[itsmoked]

One normally prefers to shield the VFD stuff to prevent the noise from getting out to other systems. You don't normally try to shield the other systems.

There are a lot of things you can do. They tend to be site specific.

Often the problems come from grounding mistakes. For instance, it's best to ground the motor directly from the VFD not ground the motor thu the local ground system.

Most of the noise is radiated from the VFD-to-motor wires. Primary to your solution is keeping that noise bottled up. The best way is to have that distance be the absolute minimum. Have the VFD mounted as close to the motor as feasible. Then run the wires thru steel conduit between the motor and the VFD to provide Faraday shielding. Make sure you run the ground with those wires in the conduit. Don't make the major error of thinking the conduit is going to work as the ground.

The high frequency edges of the waveforms are the noise menace. You can add a filter immediately next to the VFD so those edges are peeled off before your leads head to the motor.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

There is a solution if your VFDs are 20 HP at most.

Gunnar Englund

http://www.gke.org

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