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Which of the following statements are true? a. As load increases armature current decreases, regardless of excitation. b. For under and over excited motors, power factor tends to approach zero with increase in load c. With normal excitation when load is increased, change in armature current is greater than in power factor which tends to become increasingly leading. d. Both with under and over excitation, change in power factor is greater than in armature current with increase in load.

Which of the following statements are true? a. As load increases armature current decreases, regardless of excitation. b. For under and over excited motors, power factor tends to approach zero with increase in load c. With normal excitation when load is increased, change in armature current is greater than in power factor which tends to become increasingly leading. d. Both with under and over excitation, change in power factor is greater than in armature current with increase in load. Correct Answer Only d is true

V curve of synchronous motor:

When the load on an over-excited or under excited synchronous motor is increased, the rate of change of its armature current as compared with that of the power factor is less and the same can be observed by using v curves as shown below.

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Observations:

  • As the load increases armature current increases, regardless of excitation.
  • For under and overexcited motors, power factor tends to approach unity with an increase in load
  • With normal excitation when the load is increased, change in armature current is lesser than in power factor which tends to become increasingly leading.
  • Both with under and overexcitation, change in power factor is greater than in armature current with an increase in load.

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