81. A salient pole synchronous machine can stay synchronized to the man when excitation is reduced to zero provided the load is

1. 1. less than Vt2		Xd - Xq
      		2Xd Xq

   
   
   

   2. less than Vt2		Xd + Xq
      		2Xd Xq

   
   
   

   3. more than Vt2		Xd - Xq
      		2Xd Xq

   
   
   

   4. more than Vt2		Xd + Xq
      		2Xd Xq

   
   
   

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   NA

   Correct Option: A

   NA

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82. Pole shoes of a salient pole synchronous machine are so shaped at that air-gap is least in the middle and increases somewhat towards the edges. This type of construction
    

1. 1. increases flux/pole for a given excitation.

   
   
   

   2. facilitates machining of pole shoes.

   
   
   

   3. eliminates a particular harmonic.

   
   
   

   4. reduces the harmonic content of the induced voltage wave.

   
   
   

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   NA

   Correct Option: D

   NA

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83. A synchronous motor is operated from a bus voltage of 1.0 pu and is drawing 1.0 pu zero power factor leading current. Its synchronous reactance is 0.5 pu. The excitation emf of the motor will be
    

1. 1. 2.0

   
   
   

   2. 1.5

   
   
   

   3. 1.0

   
   
   

   4. 0.5

   
   
   

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   NA

   Correct Option: B

   NA

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84. A synchronous generator is loaded and the armature current lags behind the excitation emf by angle Ψ . The electrical angle between the field axis and the axis of the armature reaction field will be
    

1. 1. 90° + Ψ

   
   
   

   2. 90° – Ψ

   
   
   

   3. 90°

   
   
   

   4. Ψ

   
   
   

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   NA

   Correct Option: B

   NA

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85. A synchronous motor is running from busbars and has a torque angle of δ = 15°. The bus voltage and frequency are reduced by 10% while field current and load torque are held constant (all losses are negligible).The new torque angle will
    

1. 1. remain the same

   
   
   

   2. increase slightly

   
   
   

   3. decrease slightly

   
   
   

   4. the motor will lose synchronism

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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