Two motors in the same electrical shaft.

Hello SMCTR

1. What voltage supply into the motor?
2. What rotational speed?
3. Is it the stator, or the rotor which needs rewinding?

There may well be a mechanical reason for the using of rectangular winding, because it is more robust, and resists vibration cracking better than small fine wires.

Advise further with

Kind Regards....

Hello Sparkstation,

The motors have the following main data: 11 kW, PF 0,80, Stator 380 V - 25 A, Rotor 255 V - 28 A, 50 Hz, 1440 rpm

Just one of them have the rotor burned and have to be rewounded.

In such application the both stators are fed from the same power supply as well as the rotors, which are fed also from the same power supply (but not the same of the stator). The two rotors are synchronized, assuring the same speed at both shafts.

A typical application can be found on the dams, to close and open the "canal lock" (up and down motion). Or, on the coupled cranes, where the two motors have to assure the same motion speeds.

Best regards

Well, I never rewind motors. I just burn 'em out and send 'em to the rewind shop in Irwin. But, I have wound transformers with round and rectangular/square wire. Because of the packing factor, you just can't get as much copper in a given space when you use round and the result is heat. Sounds like you might be running these boys a little hot already. I'd vote for the rectangular.

Sorry to be that imprecise. But, If those motors share the load, and the setup does not mind, that the motor with the round instead square wire does not pick up more than 80 - 90% of its load, no problem. But, why do you bother with it, instead sending it to a professional rewinder?!? If you are too cheap, I can guarantee, it will cost you.

"Can I rewind one motor"

CAN - Yes

SHOULD - No

Were they standard Squirrel cage Induction Motors, you might have a problem. Even a slight difference in slip from one to the other will make one of them drag the other as an additional load instead of sharing the load. Rewinding, even using the exact same method and materials, will not likely end up with them being identical any longer, and using different materials / methods almost assures that.

But you apparently have Wound Rotor Induction Motors (otherwise you could not have burned out the rotor windings and would not have rotor nameplate data). WRIMs have the inherent ability to have their output torque tweaked by adjusting the rotor resistance. So all you will need to do is monitor the stator currents of both motors and adjust the rotor resistance of one of them to make them share the load. Do it under full working load however, it may be different than unloaded.

Thanks to all of you for your comments.

For such applications – electrical shafts to guarantee the same speed at the two motors – the both motors have to be electrically exactly identical.

So, the copper profile can not be changed, have to be exactly equal to the original. Moreover, during the winding the same mean length have to be maintained to assure the same resistance as the original.

If the copper profile changed from rectangular wire to 6 round wires, the resistance will not be the same, which will cause the motor-set malfunction and the rotor synchronism loss with the corresponding overheating.

The rotor resistance will be different, mainly due to "skin effect" which is proportional to the current and frequency values. Moreover, the torque characteristic will be different, which will cause bigger problems during the motors star-up and stop-down.

An alternative solution for such motors, in case of difficulty to reproduce the original winding design, will be to rewind the both rotors which will assure the same electrical data at both rotors.

You could put a limited slip differential in to account for different torques. Otherwise you may have problems with overcurrent when one motor starts acting like a generator.