Introduction:
A synchronous motor is a type of AC motor that operates at a fixed speed determined by the frequency of the power supply. Unlike an induction motor, a synchronous motor is not self-starting and requires external means to bring it up to synchronous speed before it can operate. This is due to the construction and working principle of a synchronous motor.

Construction and Working Principle:
A synchronous motor consists of a stator and a rotor. The stator has three-phase windings that create a rotating magnetic field when connected to a three-phase power supply. The rotor, on the other hand, contains field windings that produce a magnetic field. The stator and rotor magnetic fields must be synchronized for the motor to operate efficiently.

Reasons for Non-Self Starting:
There are several reasons why a synchronous motor is not self-starting:

1. No Starting Torque: Unlike an induction motor, a synchronous motor does not have any starting torque. The rotor of a synchronous motor must rotate at the same speed as the rotating magnetic field in the stator to establish synchronism. Without external means to bring the rotor up to synchronous speed, the motor will not start.

2. No Slip: In an induction motor, slip is necessary for the production of torque. However, in a synchronous motor, slip is zero because the rotor speed is always synchronized with the stator field. Without slip, there is no torque production, which hinders the self-starting capability.

3. Back EMF: When the synchronous motor is not running at synchronous speed, it acts as a generator and produces a back electromotive force (EMF). This back EMF opposes the applied voltage and prevents the motor from starting on its own.

Methods for Starting:
To overcome the non-self-starting nature of a synchronous motor, the following methods are commonly used:

1. Starting by External Means: The synchronous motor is initially brought up to synchronous speed using an external prime mover, such as another motor or a diesel engine. Once the motor reaches synchronous speed, it can operate independently.

2. Using Damper Windings: Some synchronous motors are equipped with damper windings on the rotor. These windings provide starting torque and help the motor reach synchronous speed. Once the motor is running at synchronous speed, the damper windings are shorted out.

Conclusion:
In summary, a synchronous motor is not self-starting due to the absence of starting torque, zero slip, and the generation of back EMF. External means or additional features such as damper windings are required to bring the motor up to synchronous speed before it can operate independently.