Synchronous motors are not self-starting. Since the rotating magnetic field can be represented by two stator pole revolving at synchronous speed. In the previous article, we have discussed the Working Principle of Synchronous Motor and Features of It and today we are a plan to discuss different types of synchronous motors starting methods.
The operation of the synchronous motor starting as following.
At the beginning, the rotor will experience an anticlockwise torque. When the stator pole above half of the revolutions the motor experience a clockwise torque.
That is which before the rotor move it which experience and the opposite direction torque.So the net torque in one direction and the motor will not start to rotate and it will vibrate heavily with each electoral cycle and finally overheated. The methods to start up a synchronous motor as follows.
1. At start motor runs at low frequencies :
To reduce the speed of the stator magnetic field to low enough value that the factor can accelerate and lock with it during one-half cycle of the magnetic field of rotation.
This can be done by reducing the frequency of applied electrical supply. This motor can also use to start using the help of another direct current supply.
2. Use a pony motor :
Use an external prime mover ( Pony motor) to accelerate the synchronous motor up to the synchronous speed which goes through. This is one of the commonly used synchronous motors starting methods.
The paralleling procedure and to bring the machine on the line as a generator. Then it turns off or disconnected by using a prime mover.
When the rotor of the synchronous motor gets the synchronous speed the dc excitation to the rotor is switched on. Once the synchronism is getting obtain in the established the pony motor who is decoupled.
3. Use damper winding :
The damper winding or armature winding is to install copper bars in the slots of the pole face of the rotor. These bars are shorted at the both ends.
The rotating stator field will cut these conductors and produce current as a result torque is produced on that damper winding. So the machine is starting as an induction motor.
When the motor runs at synchronous speed there is no relative motion between the damp conductor and the rotating field. So no current will produce an effect to the rotor.
4. Use as Slip Ring Induction Motor :
The slip ring induction motor starting method can also us as a squirrel cage induction motor not provide any type of starting torque.
Normally the three ends of the windings are taken through the slip rings. So and external rheostat part can installed in the series of the rotor circuit.
Hope that you have get some basic understanding regarding the starting methods which use for starting the synchronous motors.
