The four various types of torque associated with a synchronous motor are described below. Four types of torque are,
- It indicates the ability of the motor to accelerate the load. It is also sometimes called “break away torque”.
- It may be as low as 10% in case of centrifugal pumps, and as high as “200 or 250% of full load torque”, as in case of loaded reciprocating two-cylinder compressors.
- The synchronous motor possesses no self starting torque; yet in modern synchronous motors, by making proper changes in the design of damper windings, almost any reasonable torque can be developed.
- Running torque is the torque developed by the motor under running condition.
- It is determined by the output power and speed of the driven machine.
- Peak output power determines the maximum torque that would be required by the driven machine.
- The breakdown or maximum running torque of a motor must be greater than this value in order to avoid stalling of the machine.
Pull in torque
- It pertains to the ability of the machine to pull in to synchronism when changing from induction to synchronous motor operation.
Pull out torque
- It is the maximum torque that the synchronous motor will develop without pulling out of synchronism. Its value ranges from 1.25 to 3.5 times the full load torque.