Which type of motor is generally not self-starting?

The synchronous motor is not considered a self-starting motor due to the nature of its operation. In a synchronous motor, the rotor must achieve synchronous speed to lock in with the rotating magnetic field produced by the stator. However, at standstill, it cannot generate the necessary torque to start on its own because there is no relative motion between the rotor and the stator's magnetic field.

To initiate the operation of a synchronous motor, an external means, such as a companion starting motor or additional starting equipment, is typically required. Once it reaches synchronous speed, the motor will continue to run as long as it is supplied with the appropriate rotor excitation.

In contrast, asynchronous motors, which include induction motors, can start under normal running conditions where the rotor accelerates to a speed less than the synchronous speed, generating torque due to slip. Universal motors can also start on their own as they can run on both alternating and direct currents.