Starting torque of matched AC motors

Question

Starting torque of matched AC motors

wsthomas (Industrial)

(OP)

31 Oct 01 21:26

Motors 3.24HP 600V. 3PH. c/w 220V. brakes. I have had a problem with a 92’ over rail bridge crane travel motors, they are causing the crane to skew. I was told that since once motor was rewound that there is a small difference in the winding and this will causing the starting torque to be different. I feel that the biggest problem is do to the fact that the brakes are not releasing at the same time, this is also showing up when the crane is stopping (one side appears to stop before the other) Should have both drive motors have been rewound at the same time and what precentage of amperage could make a difference?

ctolbert (Electrical) · Answer 1 · 2001-11-01 07:00:25

I had the same problem with a 1960's vintage P&H DC crane. It had dual bridge motors. I found the following problems contributed to the skewing.

-brake release (I had a weak coil on one)
-brake pad wear
-popped resistor-so point to point was off on the 3rd speed
-all were rewound at least one point (not the problem per say)
-worn boggey pins (the biggest problem on the rails)
-dip in rails
-dip in hot rails (did not attribute to skewing as far as I could tell)
-dragging hot rail shoes (I redesigned this to include graphite inserts into the conducting material to aid in lubrication...worked like a champ)
-transmission shafts and pillow-blocks were shot

Maybe some of these can help you out. I suspect the brakes more than anything.

Carl

Marke (Electrical) · Answer 2 · 2001-11-06 13:40:43

The starting torque developed by an induction motor is essentially determined by the rotor design rather than the stator. If there is a significant difference in the number of staor turns, then this will have an effect though. I would suggest the the brake area is much more variable.

Mark Empson
http://www.lmphotonics.com

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Starting torque of matched AC motors