For synchronous motors, inverted V-curves are the plots of power factor versus ____________.

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NHPC JE Electrical 5 April 2022 (Shift 1) Official Paper
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  1. output frequency
  2. armature current
  3. field current
  4. supply voltage

Answer (Detailed Solution Below)

Option 3 : field current
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Inverted V – curve:

The excitation and power factor of the synchronous motor can be summed up in the following graph. This is called an inverted V curve of the synchronous motor.

RRB JE EE 77 15Q Electrical Machines 5 Hindi - Final images Q5

From the inverted V – curve,

  • The synchronous motor operates at a lagging power factor when the excitation is under excited.
  • The motor operates at a unity power factor at normal excitation.
  • The motor operates at a leading power factor when the excitation is over-excited.

Important Points

  • Under excited alternator works at the leading power factor
  • The normal excited alternator works at the unity power factor
  • The overexcited alternator works at lagging power factor
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