Constant torque or power? 1

[EngRepair]

If the three phase, 4/2 pole (one winding) motor drives the crane, what could be motor connection: constant torque or constant power?

 

[rhatcher]

The hoist will be constant torque. The 2 pole winding will have twice the horsepower of the 4 pole winding.

 

[EngRepair]

The hoist will be constant torque

This is something I was expected, but as you can see, the nameplate shows the same power in both poles.
(by the way, first winding is 4/2 pole and second is separate winding of 24 poles)

 

[rhatcher]

I'm not sure why you asked the question of constant torque or constant power if you have a nameplate that shows constant power.

 

[EngRepair]

Because I've already had several cases when the nameplate shows approx. the same power but the motor has a constant torque internal connection.
Unfortunately, the internal connection of this motor was not recorded.

 

[rhatcher]

Now I understand your question. Normally a hoist motor is constant torque. However, this nameplate does appear to show a constant power rating.

You should be able to determine which type of motor this is by examining the motor starter since the constant torque starter is different from the constant power starter.

 

[Compositepro]

The question really doesn't make sense. The motor has a capability of supplying up to a certain HP and up to a certain torque. The actual load on the motor is determined by how much weight you are lifting.

The speed and power numbers on the nameplate indicate this is a three speed motor, and that the power ratings are the same at full and half-speed. Therefore the torque capability of the motor is doubled at half speed. In the change from half to 1/12 speed, the power rating drops to 1/6 full speed. Therefore the torque capability of the motor at low speed is the same as at mid-speed but the heat dissipation capability of the motor has dropped to 1/6.

 

[rhatcher]

Compositepro,

EngRepair's question is based on finding a motor that appears to be rated for constant power used in a constant torque application. I also find this to be very unusual.

As you pointed out, when using this motor the hoist lift capability at high speed would be 1/2 of the capability of the lower speeds. This could lead to the unfortunate instance of being able to lift a load with the first two speeds only to have it drop when you went to the high speed.

The alternative, if you assume that the high speed rating is matched to the structural load capability of the crane, is that the lower speeds will be able to lift a load that is twice the weight of the structure rating, leading to a structural collapse.

In either case, I can understand his question and his concern.

 

[EngRepair]

You should be able to determine which type of motor this is by examining the motor starter

Yes, I'll try to check whether the external star connection is realized in 2 pole or 4 pole.
These concerns are occurring with european motors mostly but I have not managed to find some IEC regulations or recommendations for constant power two speed motors.
Does anyone know something about them?

 

[petronila]

Hello Eng Repair

Usually in Europe for dahlander motors(two speed one winding)the OEM uses two possible connections: Constant horse power and Variable Torque, in NEMA motors also you can find constant torque.

In constant horse power the power is the same and in variable torque the Low-speed horsepower is one-fourth or in some cases one-sixth
of high-speed horsepower.


Taking account your motor is european and the name plate provided my oppinion is the motor is variable torque then the winding connections are two wyes (High)/ one wye (Low).


Regards

Carlos