Variable speed drive cable

[deere]

Is variable speed drive cable a must on the load side of a vfd?

 

[Skogsgurra]

Belden says so. But Belden has an agenda.

It depends a lot. There are at least four reasons why special cable may be good between VFD and motor. EMC is one, capacitve loading of inverter is another, ozone production and insulation deterioration a third and good, symmetrical PE a fourth.

You can run any motor/inverter on any cable. It will work, provided basic requirements are fulfilled. But you may get EMI problems and capacitive loading of the IGBT switches may be too high. Over the time, ozone production in the cable may, at least at higher voltages, lead to insulation being brittle and breaking down.

Motor reactors, du/dt filters and other filters reduce the problem. It is your decision. No definitive answer can be given without knowing the system and the environment.

If in doubt, use VFD cable in one installation and standard cable in another. In five years time, you will know what you need in your applications.



Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[MAGTiger]

I think you will find a properly sized dv/dt filter with armored cable (again properly sized) to be a more cost effective solution. The problem with the VFD cable is that it is basically jus protecting itself. You will still get ring-up at the motor terminals. One of the really big problems I see in long lead applications is gross oversizing of the cables. Yes, I understand the need to reduce voltage drop. But understand that when you increase cable size, you increase capacitance. So don;t oversize any more than absolutely necessary. I once saw a 50hp application where the contractor used 250mcm cable for a 600ft run because it's what he had on the truck. What a waste, and it caused huge problems in the cable, the thing had more than 3 amps of common mode current.

Neil

 

[jraef]

Ozone production, that's a new one on me. But I trust Gunnar to be up on these things.

Maybe I shouldn't, but I'm like that...

MAGtiger,
Using the specialty cable does help with the standing wave generation issue because that is partly dependent on cable capacitive coupling, which can be reduced by having the three cables individually shielded. I'm not saying this is a panacea either, just that your depiction of it being useless is a little harsh. I tend to lean towards filters myself, but different strokes for different folks and as Gunnar said, it really takes careful evaluation on a case by case basis.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[dpc]

For those in North America, Okonite's CLX armored cable is now provided with three interstitial ground wires as standard and can provide much of the benefit of a special shielded drive cable (at least according to Okonite .

(No financial interest in Okonite - just fyi for those using CLX for other applications).

 

[MAGTiger]

I'll qualify my statement by saying that the VFD cable we have test experience with was purchased around 10 years ago and frankly I don't know if it has individually shelded strands. But we did ground the shield and our results were that the overvoltage ringup was not as bad as the armored cable but the common mode current was worse. I decode that as meaning an improvement in impedance match with the motor but more capacitive coupling to ground.

Neil