Correct Answer - Option 4 : Breakdown torque
Starting torque: It is the torque developed by the motor when full voltage is applied to its stator winding.
Synchronous torque or Running Torque: It is the torque that acts on the shaft of a synchronous machine when the rotational speed of the rotor deviates from the synchronous speed and that keeps the machine in synchronism.
Pull-in torque:
- A synchronous motor is started as an induction motor during starting condition and its speed below 2 to 5% of the synchronous speed
- When the excitation (DC supply) to the field winding is applied, the motor pull into synchronism resulting stator and rotor magnetic field rotates at the same speed
- The amount of torque requires for the synchronous motor to pull into synchronism is called as pull in torque
Pull-out torque:
- It is maximum torque that the synchronous motor can develop without pulling out of step
- When the synchronous motor is loaded, the rotor falls back by some angle a is called a load angle
- The stator and rotor magnetic rotate at synchronous speed in spite of some load is applied on the rotor
- The synchronous motor developed maximum torque when the rotor falls back by angle 90°
- When the load increases beyond its maximum rating, the rotor steps out of synchronism and synchronous motor stop.
