Constant Torque Operation in Motors

Constant Torque Operation refers to the operation of the motors at a fixed torque value.  The torque supplied by a motor is dependent on the load.  However, a motor which has a constant flux is considered to be running at constant torque.

For a motor to run at constant torque it has to be driven by an AC drive.  AC drives are able to vary the frequency and the voltage such that a constant V/Hz value is obtained.  The V/Hz is the ratio of voltage to the frequency in an electric machine.

When the frequency of the motor is adjusted, the stator reactance changes.  This reduces or increases the stator current.  To correct this, the voltage has to be adjusted. 

The conveyor is an example of an application which requires a constant load.