VFD for Conical Rotor Motor

[Drivesrock]

Hi all.

We have a customer with an overhead travelling crane with a conical rotor motor on the main hoist. This was a recente upgrade. The motor is DOL and when energised, the rotor aligns and opens the integral brake but the inrush current is causing voltage dips in his factory. Especially annoying during the jog movements!

Has anyone successfully installed a VFD on a motor like this? 30kW, 440V, 4 pole, 60Hz motor.

The hoist supplier said no, one VFD supplier told customer it's not possible, another said "don't know". I think it should be possible - with a vector control VFD (possibly overrated for extra torque at start) + encoder - but hunting around and I don't seem to get a definitive answer.

 

[itsmoked]

Jraef will know. He'll be along. 20 years solving VFD issues and many cranes.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dArsonval]

Conical rotor motors are also brakes. The tapered design of the rotor mating with the tapered stator bore serves as a brake.
It's been a long time since I've dismantled a motor of this type, but I'm recalling a fairly heavy spring is incorporated into its functioning design as well.

In essence, this kind of motor is a rotating solenoid for lack of a better description.

It has to be fully on or off to properly function.

John

 

[waross]

The torque depends on the slip frequency. A VFD driven motor may deliver full torque at standstill. That equates to full centering force on the conical rotor.
I'll wait for Jeff for specific details.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Bill West]

I Googled this type of device, the Demag brand shows a separate brake drum & shoe. It is nonetheless operated by the rotor's solenoid action aside from its load hoisting torque action. It looks like a very sound, simple approach to nearly fail safe automatic braking. Would that safety feature be put a risk by a VFD drive? If a malfunction in the VFD could cause the rotor to pull-in without giving it enough rotational torque to prevent the load from self lowering then we would have a problem.

On a new piece of equipment I don't think I would pass up the maker's guarantee and especially his design responsibility for the product's safety.

Could the flicker be reduced by a stiffer supply? Is there a way to separate the lighting? We'd have to know the plant's basic system out through the utility transformer.

Bill