VFD to Motor 1

[Humble2000]

I am working on a job that consultants ask for a VFD cable from VFD to motor.This cable has a seperate ground for each phase.First time that I have heard of this practice.any idea the concept behind this practice??

Thank you

 

[Skogsgurra]

There are some benefits in using a completely symmetric motor cable. Belden has something to say in

http://www.engineeringtalk.com/news/bez/bez100.html

and there are many others that have special cables for VFD/motor connection.

The alternative is to use a sine filter or an inverter with a sine-wave output. In both cases, you can use standard motor cables.

Using a separate shield on each phase is a bit extreme, but it will surely reduce the ozone build-up in the cable and make it live longer. Ground all shields (low-impedance connections!) at both inverter and motor ends. Keeps motor frame voltage down and also reduces EMI.

There is one thing that you should check; the capacitance to ground will probably be quite high with this cable and it may cause additional losses in the IGBTs if the cable is long. If that is the case, you may also need to add motor reactors.



Gunnar Englund

http://www.gke.org

 

[dpc]

It helps reduce RFI from the cable. Okonite C-L-X or similar metalclad cable is a good choice for VFD to motor wiring. It now comes standard with three interstitial ground wires.

 

[ozmosis]

Humble2000
What is the cable length between VFD and motor? Most drive manufacturers will stipulate screened motor cable (to meet levels of radiated RFI emissions ) but they will also stipulate a motor cable length to back these claims up. Too long a screened cable and, as Gunnar says, the increased capacitance will potentially create more problems than this sort of cable will solve.

 

[inverterdude]

this special cable is also very good to minimize parasitic motor bearing currents by creating a low impedance path to ground for the high frequency common mode voltage.