Which of the following is not considered in the case of synchrono

SOLUTION

Synchronous motor:

• A synchronous motor is one in which the rotor normally rotates at the same speed as the revolving field in the machine.
• The stator is similar to that of an induction machine consisting of a cylindrical iron frame with windings, usually three-phase, located in slots around the inner periphery.
• The difference is in the rotor, which normally contains an insulated winding connected through slip rings or other means to a source of direct current.

Principle of Synchronous motor:

• The principle of operation of a synchronous motor can be understood by considering the stator windings to be connected to a three-phase alternating-current supply.
• The effect of the stator current is to establish a magnetic field rotating at synchronous speed. A direct current in a p-pole field winding on the rotor will also produce a magnetic field rotating at rotor speed. At a particular instant rotor and stator poles might be of the same polarity (N-N or S-S) causing a repulsive force on the rotor and the very next instant it will be N-S causing attractive force. But due to the inertia of the rotor, it is unable to rotate in any direction due to that attractive or repulsive forces, and the rotor remains in standstill condition. Hence a synchronous motor is not self-starting.
• So Motor starting with an external prime Mover or damper winding by placing on the rotor poles.

Synchronous motor behavior on no-load:

The power factor of the stator electrical input can be directly controlled by the adjustment of the field current.

• At overexcitation motor works on leading power factor
• At normal excitation motor works on unity power factor
• At under excitation, motor works on lagging power factor

The main feature of synchronous motor:

• The speed of the synchronous motor is independent of the load, i.e., the variation of the load does not affect the speed of the motor.
• The synchronous motor is not self-starting. The prime mover is used for rotating the motor at their synchronous speed. 
• The synchronous motor operates both for leading and lagging power factor. The synchronous motor can also be started with the help of the damper windings.