Ø QUE-ANS:10-30 words

[1]        A synchronous motor starts as usual but fails to develop its full torque. What due to?
  1. Exciter voltage may be too low
  2. Field spool may be reversed
  3. There be either open circuit or short-circuit in the field.
[2]        Under which conditions a synchronous motor will fail to pull into step?
  1. No field excitation 2. Excessive load 3. Excessive load inertia
[3]        Does change in excitation affect the synchronous motor power factor? How?

Yes. When over-excited, synchronous motor has leading power factor. However, when under Excited, it has lagging power factor.

[4]        For what service are synchronous motors especially suited?

For high voltage service.

[5]        Which has more efficiency; synchronous or induction motor?

Synchronous motor.

[6]        Mention some specific applications of synchronous motor?
  1. Constant speed load service 2. Reciprocating compressor drives 3. Power factor correction. 4. Voltage regulation of transmission lines 5. Propulsion system 6. Bow thruster
[7]        What is a synchronous capacitor?

An overexcited synchronous motor is called synchronous capacitor, because like a capacitor, It takes a leading current.

Ø 30-60 words

[1]        What could be the reasons if a synchronous motor fails to start?

It is usually due to the following reasons;

  1. Voltage may be too low
  2. Some faulty connection in auxiliary apparatus
  3. Too much starting load
  4. Open-circuit in one phase or short-circuit
  5. Field excitation may be excessive.
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