Induction Motor MCQ Part 7

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The starting torque of 3 phase induction motor is maximum at which value of rotor power factor:

  1. 0.3 lag
  2. 0.685 lag
  3. 0.707 lag
  4. None of above

Correct answer: 3. 0.707 lag

Explanation:

Rotor power factor is mathematically expressed as:

R.PF = R2/√(R22 + X22)

Rotor power factor is maximum when R2 = X2

R.PF = R2/√(R22 + R22)

= R2/{R2√2}

= 1/√2 = 0.707 lag

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