86. Synchronous generator voltage obtained by the synchronous impedance method is
    

1. 1. higher than actual as it does not account for magnetic saturation

   
   
   

   2. lower than actual as it does not account for magnetic saturation

   
   
   

   3. nearly accurate as it accounts for magnetic saturation

   
   
   

   4. nearly accurate as the generator is normally operated in the unsaturated regi on of magnetization

   
   
   

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   NA

   Correct Option: A

   NA

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87. The subtransient reactance of a synchronous generator is much less than its synchronous reactance in the initial phase of short circuit from no load as
    

1. 1. magnetizing ampere-turns appear because of induced field and damper winding current as the air-gap flux cannot change instantaneously from its no load value.

   
   
   

   2. demagnetizing ampere-turns appear because of induced filed and damper winding currents as the air -gap flux cannot change instantaneously from its no-load value.

   
   
   

   3. magnetizing ampere-turns, appear because of induced field and damper winding currents as the air-gap flux must reduce instantaneously from its no-load value.

   
   
   

   4. demagnetizing ampere-turns appear because of induced field and damper winding currents as the air-gap flux must reduce instantaneously from its no-load value.

   
   
   

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   NA

   Correct Option: A

   NA

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88. A synchronous motor with 5 Ω synchronous reactance (negligible resistance) draws a leading current of 10 A at 400 V. The induced emf is
    

1. 1. 400 + j √3 × 50

   
   
   

   2. 400 – j √3 × 50

   
   
   

   3. 400 – √3 × 50

   
   
   

   4. 400 + √3 × 50

   
   
   

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   NA

   Correct Option: D

   NA

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89. The startor of a salient pole synchronous generator is excited from a low voltage 50 Hz supply while the rotor is made to run at a slip of 0.05. The reluctance presented to the rotating startor mmf is
    

1. 1. constant

   
   
   

   2. varies sinusoidally at 525 Hz

   
   
   

   3. varies sinusoidally at 0.25 Hz

   
   
   

   4. varies sinusoidally at 2.5 Hz

   
   
   

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   NA

   Correct Option: D

   NA

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90. x_d = d-axis synchronous reactance, x_q = q-axis synchronous reactance In a salient pole synchronous machine
    

1. 1. x_q > x_d

   
   
   

   2. x_q = x_d

   
   
   

   3. x_q < x_d

   
   
   

   4. x_q = 0

   
   
   

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   NA

   Correct Option: C

   NA

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