The synchronous motor is made self-starting by providing a special winding on the rotor poles, known as damper winding or squirrel cage winding. AC supply given to the stator produces a rotating magnetic field which causes the rotor to rotate.
How can a synchronous motor be self starting?
Answer: The synchronous motor itself does not have the ability to self-start. However, the addition of an additional winding known as damper winding (similar to squirrel cage motor) enables it to self-start. This damper winding is linked with the rotor, and works on the principle of induction motor.
Why synchronous motors are self starting?
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator.
How does a synchronous start?
The motor is first started as a slip ring induction motor. The resistance is gradually cut-off as the motor gains speed. When it achieves near synchronous speed, DC excitation is given to the rotor, and it is pulled into synchronism. Then it starts rotating as a synchronous motor.
How does a 3 φ synchronous motor start?
A three-phase synchronous motor has no starting torque. … Once up to speed, the rotor field can be excited with direct current and the rotor is, in effect, then dragged around at the same speed as the three-phase stator field.
Which motors are self-starting?
Three-phase induction motor is self-starting, because winding displacement is 120 degrees for each phase and supply also has 120 phase shift for 3-phase. It results in a unidirectional rotating magnetic field is developed in air gap which causes 3-phase induction motor to self-start.
How do you test a synchronous motor?
TESTING THE SYNCHRONOUS MOTOR
The rotor can be tested with an ohmmeter for an open winding or a grounded winding. To test the rotor for an open winding, connect one of the ohmmeter leads to each of the slip rings on the rotor shaft, Figure 17–5.
Why DC motors are not self starting?
A DC Motor is a self start motor. As soon as supply is given to the motor it starts rotating. A motor which does not self start is single phase induction motor. This motor fails to start because it is unable to develop a rotating magnetic field therefore fails to generate initial torque.
Why induction motors are not self starting?
As discussed above, single phase induction motors are not self-starting because a single phase supply cannot produce a rotating magnetic field. We require a two phase or three phase supply for the production of rotating magnetic field. But we can create a rotating magnetic field by a two-phase construction.