Replacement of Slip Ring Motor With 'Squirrel Cage Motor & VFD'

TonyS is correct and he is giving you good advise. GA to him. My limited experiences with crane motors brought me in touch with DEMAG http://www.demagcranes.us/ They are very helpful, and have some great products.

Klearzen

I agree with you Demag do make some of the best cranes all be it somewhat over engineered. Have you ever tried to release one of their taper brake motors? They are weird and the only way to release them was mindless violence with a large mallet!

why is it tapered

Hi Atul,

Now a days many of the customers opt for Sq.Cage motors with VFD as they have lesser problems with maintenance. Such motors are Cranes Duty motors which are designed for Crane applications such as high starting torque, frequent reversing, and higher switching per hour.These motors are successfully working on many cranes.

OK I stand corrected, but in my defence of the 50+ cranes I've worked on only one had VFD drives and it was a pain in the ****

BTW it was made by Demag

My Dear Sir,

As you had already said Demag offers Conical Rotor Motors which are difficult to maintain as air gap between stator and rotor is very critical. Some times due to wear of brake liner it changes or in dusty atmosphere rotor gets jammed.

My previous company from where I retired had German Collaborators hence we had above motors for cranes and hoists. Conical Rotor Motors were more known in European countries and in India it was new phenomena.

I had to train many customers regarding maintenance of the above motors. These motors have advantage of being compact and elimination of additional E.M Brakes but one should know servicing aspect of such motors.

Regards,

Suresh Sharma.

I had used VFD on Demag conical brake motors and also on the fast motor only in microspeed units again with no problems. I used these extensively at Ford Motor with no real issues.

I once had to replace an ABB ACS550 series as this could not cope with this motor so I suppose some makes of VFD are not so happy but both FUJI and CT worked well, the FUJI right down to <1Hz both starting and stopping with accurate control.

Another interesting point is that since the brake now works normally as a holding brake only, wear and maintenance becomes less of an issue as the VFD does all the work!

A point to beware is going overspeed too much the underfluxing will cause the brake to start applying so it's better to stick to the region of the motor's rated maximum speed.

I've used VFD on slip ring and IM for both travel and hoist applications.

I have heard of reports of various VFD that are not specialised or well suited to these applications (particularly hoist) because of setup and functions (e.g brake control at starting and stopping) and also because of their limited overlaod capability (selection??).

Especially hoist though, many VFDs offer limited overload capability and also control is not so good at low speeds (critical). So some are not so suitable and others may need oversizing to cope with the accelerating and decelerating torques involved.

I've used FUJI Electric very successfully but I would suggest you speak to suppliers with experience of these applications who can refer you to customers confirming this suitability and experience.

It's no application for a general purpose piece of equipment supported by people with no experience of your applications.

I haven't really seen any particular problems with IM motors to replace SR and so can't add to comments of others' experiences - I've had no problems with IM but I have used good performance VFD and adequate sizing and also have application experience. Personally, I might change the ramp times to keep torque to 200% maximum, well inside the motor's capability that I have used.

I have worked on both DC and AC driven cranes. They both have their own set of issues when you begin maintaining them. As far as operations go, if you didn't know what you were driving you couldn't tell. Lots of good manufactures of equipment out there, just choose "Crane duty Motors" and you won't go wrong.

The only other thing I could add to this is training for maintenance staff. You will need to make sure that the what ever you do, have the employees who are to maintain units. Trained in the proper trouble shooting and repair of the controllers and motors.

How will you control the speed? Or are you planning to add VFDs?

you have had some really great answers.. I suggest you got to a crane designer/manufacturer and get a crane company to do it for you.

Convert the existing slip ring motor to induction motor by shorting the sliprings. Connect the VFD and RUN your application.