151. A 6-pole, 50 Hz wound rotor induction motor when supplied at the rated voltage and frequency with slip-ring open-circuited, developed a voltage of 100 V between any two rings. If rotor is driven by an external means at 1000 rpm opposite to then direction of startor field, the frequency of voltage across an slip-rings will be

1. 1. zero

   
   
   

   2. 50 Hz

   
   
   

   3. 100 Hz

   
   
   

   4. 200 Hz

   
   
   

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   NA

   Correct Option: A

   NA

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152. In a 3-phase squirr el cage induction motor, skewing of rotor slots reduces

1. 1. parasitic torque and noise but increases pullout torque

   
   
   

   2. parasitic torque and noise but increases starting torque

   
   
   

   3. noise but increases pull out torque and parasitic torque

   
   
   

   4. parasitic torque, noise pullout torque and starting torque

   
   
   

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   NA

   Correct Option: D

   NA

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153. An induction motor and synchronous motor are connected to a common feeder line. To operate the feeder line at unity pf, synchronous motor should be

1. 1. under-excited

   
   
   

   2. over-excited

   
   
   

   3. normally excited

   
   
   

   4. disconnected from the common terminals

   
   
   

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   NA

   Correct Option: B

   NA

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154. Mmf produced by the current of a 3-phase induction motor

1. 1. rotates at the speed of rotor in the air gap

   
   
   

   2. is stand still with respect to startor mmf

   
   
   

   3. rotates at slip speed with respect to startor mmf

   
   
   

   4. rotates at synchronous speed with respect to rotor

   
   
   

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   NA

   Correct Option: B

   NA

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155. If rotor power factor of a 3-phase induction motor is 0.866, then spat ial displacement bet ween startor magnetic field and rotor magnetic field will be

1. 1. 30°

   
   
   

   2. 90°

   
   
   

   3. 120°

   
   
   

   4. 150°

   
   
   

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   NA

   Correct Option: C

   NA

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