Why synchronous motor is self starting

You must be aware of rotating magnetic fiel if not please refer my answer for this ques: How synchronous motor is independent of voltage change explain briefly? Now you know what is rotating magnetic fiel you think how fast it is rotating? This stator may be single or three phase.

Now, if we supply ac to stator,a magnetic field will produce in rotor,and rotor will rotate in synchronous speed with stator field. It does not require nay external mean to rotate.

However, in this case, the rotor has its own field produced by .

Synchronous motors are inherently not self starting.

They require some external means to bring their speed close to synchronous speed to before they are synchronized. The speed of operation of is in synchronism with the supply frequency and hence for constant supply frequency they behave as constant speed motor . This video is about the reason that synchronous motor is not self - starting ? Working of synchronous motor is elaborately explained in this video animation. This video explains how constant speed characteristics of synchronous motor is achieve and why they are not self starting and use of damper winding to make them self start.

All the advantages of synchronous motors are equally balanced by the drawbacks of being non- self starting. As the synchronous motors are non self - starting in nature, they have to be started by some external means and has to brought to synchronous speed. The reason behind this is very interesting. DC motors are self starting because the angle between the magnetic field of the rotor and the stator is fixed by the design of the motor.

However, the synchronous motor is not self starting and must still be brought up to the approximate alternator electrical speed before it will lock . Methods of starting synchronous motor. It can run either at synchronous speed or not at all i. Some auxiliary means has to be used to start the motor. The working principle of an ac machine is primarily one field following another field. The damper winding consists of short circuited copper bars embedded in the face of.

Induction motor (squirrel cage) are much cheaper to manufacture. The synchronous machine , however, is not self - starting. A single phase synchronous motor is not self - starting.

An induction motor can therefore be made without electrical connections to the rotor. The figures show an elementary alternator and an elementary synchronous motor , the construction of each being identical as shown. But if the rotor has got no initial rotation, situation is quite different.

North Pole of the Rotor will obviously get attracted by South Pole of RMF, and will start to move in the same direction. But since the rotor has got some inertia, this starting speed will be very low.