66. The startor of a 415 V, 50 Hz, 6-pole, 970 rpm, 3-phase slip-ring induction motor is fed with normal voltage. The rotor with slip rings opencircuited is rotated at 500 rpm along the normal direction of it s rotation. The frequency of the voltage across slip rings will be _______ HZ.

1. 1. 5 Hz

   
   
   

   2. 25 Hz

   
   
   

   3. 21 Hz

   
   
   

   4. 45 Hz

   
   
   

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   NA

   Correct Option: B

   NA

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67. A 200/100 V, 50 Hz transformer is to be excited at 40 Hz from the 100 V side. For the exciting current to remain the same, the applied voltage should be _______ V.

1. 1. 10 V

   
   
   

   2. 30 V

   
   
   

   3. 40 V

   
   
   

   4. 80 V

   
   
   

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   NA

   Correct Option: D

   NA

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68. A single-phase transformer when supplied from 220V, 50 Hz has eddy current loss of 50 W. If the transformer is connected to a voltage of 330 V, 50 Hz, the eddy current loss will be_______ W.

1. 1. 112.5 W

   
   
   

   2. 12 W

   
   
   

   3. 515 W

   
   
   

   4. None of the above

   
   
   

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   NA

   Correct Option: A

   NA

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69. If 1.8° step, 4-phase stepper motor has a total of 40 teeth on 8 poles of startor, then number of rotor teeth for this motor will be
    

1. 1. 40

   
   
   

   2. 50

   
   
   

   3. 100

   
   
   

   4. 80

   
   
   

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   NA

   Correct Option: C

   NA

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70. In an ac servometer, the control winding is supplied with input voltage of
    

1. 1. same frequency as the reference winding voltage but with 90° phase difference.

   
   
   

   2. same frequency as the reference windings voltage and also having same phase.

   
   
   

   3. any frequency compared to t he reference winding but with 90° phase difference.

   
   
   

   4. any frequency compared to the reference winding but of the same phase.

   
   
   

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   NA

   Correct Option: A

   NA

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