Dear Readers, Welcome to SYNCHRONOUS MOTOR Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of SYNCHRONOUS MOTOR. These SYNCHRONOUS MOTOR Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT & Non IT Industries.
Ans: a. the motor is not inherently self starting
b. The speed of operation is always in synchronous with the supply frequency irrespective of load conditions
c. The motor is capable of operating at any power factor.
All dc and ac motors work on the same principle. Synchronous motor operates due to magnetic locking taking place between stator and rotor magnetic fields.
• By an extra 3 phase cage induction motor
• By providing damper winding in pole phases
• By operating the pilot excitor as a dc motor
The speed of operation remains constant from no load to maximum load in the motor operating at constant frequency bus bars.
Synchronous motor work on the principle of force developed due to the magnetic attraction established between the rotating magnetic field and the main pole feed. Since the speed of rotating magnetic field is directly proportional to frequency the motor operates at constant speed.
The rotating magnetic field is initially established by the prime source of supply V. The main field then causes an emf e to get induced in the 3 phase winding. Hence when the machine operates as a synchronous motor the emf phasor always lags the terminal voltage phasor by the load1torque angle .
When its load angle is equal to the impedance angle .
The variation of magnitude of line current with respect to the field current is called V curve . The variation of power factor with respect to the field current is called inverted V curve.
Increase in emf causes the motor to have reactive current in the leading direction. The additional leading reactive current causes the magnitude of line current, accompanied by the decrease in power factor.
A synchronous motor used to change the power factor or power factor in the supply lines is called synchronous phase modifier.
A synchronous motor operated at no load with over excitation condition to draw large leading reactive current and power is called a synchronous condenser.