VFD Application in slip ring induction motor...

Hello kmshanavaz

You have not advised your Location or Country (Easily done by you in your Member Profile) - so this reply is a general one.

You do not advise the number/size of the strands.

The machinery is perhaps quite old, as these days a VFD with each squirrel cage motor would normally be used, instead of wound rotor motors, the units variable speed and synchronised for the production rate at the cable drawing plant.

So, from the figures you quote, it would be more efficient to change to squirrel-cage motors with VFD's.

If you do the changeover, and the Cable Makers can afford the extra, it would be efficient to also install an Automatic Power Factor Correction Unit to the Works.

You would need to carefully cost out the above, as the energy savings may take a couple of years or more to recover the capital cost of changing over.

Advise your progress here please.

Kind Regards....

thank you Mr.Sparkstattion for your quick response....again i would like to know whether the VFD can withstand these high starting torque? whether the motor will run?.....

Yes it will run. Just make sure you get a VFD that will take the amount of current you are putting through it. Also, don't skimp on the VFD that you get. You can get rather inexpensive drives, but I would go with a heavier duty for something this critical. I would also highly recommend doing as Sparkstation suggested and going to an inverter duty squirrel cage motor.

I have put VFD's into wound rotor motor applications before by just shorting the sliprings on the motor, but it's usually for something that isn't critical to production if it breaks.

Yes. a VFD can stand high starting torques assuming the rating of the VFD matches the motor. I've been using VFD for quite sometime in our extruders.

However, i think it would be an issue if you will be using it in a high rpm plastic granulator as the starting is very slow. If the granulator "ate" too much of plastic, the VFD is slow in regaining speed.

Be aware to select a VFD with a high starting torque.

Slipmotors usually have high starting torques, and not all VFD can control the motor to deliver the high starting torque.

Do not use VFD that are normally used for pumps or ventilation.

good luck

For the fundamental frequency (50 or 60 Hz according where you live ), you do not need a Power factor capacitor. The Power factor will always be 1. This is not correct for the higher harmonics...