VFD with Dahlander winding motors

[fab1961]

Dear all,
I have been reading threads 237-345587 and 237-268932, still I feel I need some advice.
We have small (4.4/3.3 kW) 2-4 poles motors that originally were meant to run at two fixed speeds.
The winding is Dahlander YY/delta.

Now we have to add a VFD to get ramps and unlimited number of speeds (of course taking care of
heating at low speeds and loss of torque over 50 Hz). The load is a rollerway carrying material,
so more or less constant torque application.

I wonder if I can simply connect the VFD wiring the motor at low speed without any rewiring etc.
After all, the VFD will see a winding - it does not know that it can be arranged in a different way ...

Thank you

 

[Skogsgurra]

Yes, of course you can. As long as the VFD outputs the correct V/f ratio.

That's the quick and easy answer. And it will probably work quite well. At least for some time.

If the motor is an older one, and Dahlander motors usually are, then the windings will have a problem with the steep PWM edges and the ringing. After some time, most "Non-VFD" motors break down because of ozone produced by partial discharge and you will have to rewind or change the motor.

You can avoid the insulation problems by adding motor reactors, but they may cause other problems. The most common is that the reactors can get quite hot if the motor cables are long (ringing between reactor leakage inductance and cable capacitance). The ringing can be reduced by adding parallel resistors to the reactors

But I think that it will be better in the long run to buy a standard VFD "hardened" motor. You will get a working installation and don't have to worry about problems popping up when you least want it. Keep the Dahlander motor as a spare.


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.

 

[fab1961]

Thank you, it is always very helpful exchanging ideas with people in the know.

 

[LionelHutz]

Your motor is a constant torque 2-speed motor. I would not expect you can run over 50Hz under load so using the high speed connection may be more suitable for your application.