Say i have a 400hp ac 3-phase motor.speed is given as 3575 rpm.Does this mean that if left to run on it's own (with 60hz and the related voltage etc) or unloaded it would produce 3575rpm? and the torque would just be power/speed?if this is the case, does this mean that if i loaded the motor with double this torque its speed would half?Basically i'm trying to figure out how to work out the performance characteristic of a motor for different loads given the basic manufacturers data.thanks...
No the speed would not be half, the power consumption would rise. You need to review the motor manufactures performance curves to find it's characteristics.
This is a 3 phase induction motor. The field rotates at 3600 RPM's and the squirrel cage rotor rotates at 3575 RPM at full load. The slip speed is the difference of field rotation and squirrel cage rotation speed. The slip speed causes a current to be introduced into the squirrel cage rotor which in turn generates the magnetic field in the cage that causes it to rotate in the first place. At no load the slip speed drops so the rotor spins at nearly 3600 RPM.
