126. The pole shoes of a synchronous machine are so shaped that the air-gap is least in the middle and increases towards the pole edges. This type of construction

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

   
   
   

   2. eliminates a particular harmonic

   
   
   

   3. gives a nearly sinusoidal waveform of output voltage

   
   
   

   4. facilitates machining of pole shoes.

   
   
   

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   NA

   Correct Option: C

   NA

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127. In a generating synchronous machine, the rotor field

1. 1. lags the startor field and electromagnetic torque is developed in a direction opposite to the direction of rotation of rotor.

   
   
   

   2. lags the startor field and electromagnetic torque is developed in the direction of rotation of the rotor.

   
   
   

   3. leads the startor field and electromagnetic torque is developed in the direction opposite to that of rotation of the rotor.

   
   
   

   4. leads the startor field and electromagnetic torque is developed in the direction of rotation of the rotor.

   
   
   

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   NA

   Correct Option: C

   NA

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128. For a given number of turns/pole/phase, the effect of winding distribution in a synchronous generator is to

1. 1. increase induced emf but to reduce the harmonic content of the wave form

   
   
   

   2. increase induced emf and also the harmonic content of the wave form

   
   
   

   3. reduce induced emf but to increase the harmonic content of the wave form

   
   
   

   4. reduce induced emf and also the harmonic content of the wave form

   
   
   

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   NA

   Correct Option: A

   NA

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129. A synchronous motor is operating on no-load at unity power factor. If field current is increased, the power factor will become

1. 1. leading and the current will decrease

   
   
   

   2. lagging and the current will increase

   
   
   

   3. lagging and the current will decrease

   
   
   

   4. leading and the current will increase.

   
   
   

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   NA

   Correct Option: D

   NA

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130. Synchronous generators used in thermal power stations have

1. 1. cylindrical rotors

   
   
   

   2. slip-rings and brushes

   
   
   

   3. startor slots in multiples of 6

   
   
   

   4. all of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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