301. A three-phase synchronous motor connected to ac mains is running at full load and unity power factor. If its shaft load is reduced by half, with field current held constant, its new power factor will be
     

1. 1. unity

   
   
   

   2. leading

   
   
   

   3. lagging

   
   
   

   4. dependent on machine parameters

   
   
   

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   NA

   Correct Option: B

   NA

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302. The electromagnetic torque T_e of a drive, and its connected load torque T_L are as shown below. Out of the operating points A, B, C and D, the stable ones are
     
     

1. 1. A, C, D

   
   
   

   2. B, C

   
   
   

   3. A, D

   
   
   

   4. B, C, D

   
   
   

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   Electromagnetic torque T_e decrease with increament in speed in stable operating zone.
   

   Correct Option: C

   Electromagnetic torque T_e decrease with increament in speed in stable operating zone.
   

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303. The dc motor, which can provide zero speed regulation at full load without any controller, is
     

1. 1. series

   
   
   

   2. shunt

   
   
   

   3. cumulative compound

   
   
   

   4. differential compound

   
   
   

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   Shunt motor has a constant speed characteristic.
   
   

   Correct Option: B

   Shunt motor has a constant speed characteristic.
   
   

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304. In a transformer. zero voltage regulation at full load is
     

1. 1. not possible

   
   
   

   2. possible at unity power factor load

   
   
   

   3. possible at leading power factor load

   
   
   

   4. possible at lagging power factor load

   
   
   

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   Zero voltage regulation at full load is possible at leading power factor load as
   

   % Reg =	IR cos φ - I × sin φ	× 100
   	V2

   
   = V₂ is the secondary voltage
   

   Correct Option: C

   Zero voltage regulation at full load is possible at leading power factor load as
   

   % Reg =	IR cos φ - I × sin φ	× 100
   	V2

   
   = V₂ is the secondary voltage
   

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305. Consider the transformer connections in a part of a power system shown in the figure given below. The nature of transformer connections and phase shifts are indicated for all but one transformer.
     
     Which of the following connections, and the corresponding phase shift θ , should be used for the transformer between A and B?
     

1. 1. Star – Star (θ = 0°)

   
   
   

   2. Star – Delta (θ = – 30°)

   
   
   

   3. Delta – Star (θ = 30°)

   
   
   

   4. Star – Zigzag (θ = 30°)

   
   
   

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   Equal phase shift of points A and B with respect to source from both bus paths.

   Correct Option: A

   
   Equal phase shift of points A and B with respect to source from both bus paths.

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