156. Speed of 3-phase induction motor is controlled from 1 pu to 2 pu using a variable frequency inverter. The equivalent circuit parameter most likely to vary is

1. 1. startor leakage inductance

   
   
   

   2. rotor leakage inductance

   
   
   

   3. magnetising inductance

   
   
   

   4. core loss resistance

   
   
   

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   NA

   Correct Option: B

   NA

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157. A 3 phase squirrel case induction motor has a full load efficiency of 0.8 and a maximum efficiency of 0.9. If it is operated at a slip of 0.6 by applying a reduced voltage, then efficiency of the motor at this operating point

1. 1. less than 0.4

   
   
   

   2. greater than 0.6

   
   
   

   3. in the range of 0.8 to 0.1

   
   
   

   4. none of these

   
   
   

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   NA

   Correct Option: A

   NA

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158. A 3-phase induction machine draws active power ‘P’ and reactive power ‘Q’ form the grid. If it is operated as a generator, P and Q will respectively be

1. 1. positive and negative

   
   
   

   2. negative and negative

   
   
   

   3. positive and positive

   
   
   

   4. negative and positive

   
   
   

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   NA

   Correct Option: D

   NA

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159. Phase splitting can be accomplished in a singlephase induction motor by

1. 1. adding a capacitor in series with auxiliary winding.

   
   
   

   2. causing auxiliary winding to have high resistance

   
   
   

   3. both (a) and (b)

   
   
   

   4. none of these

   
   
   

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   NA

   Correct Option: C

   NA

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160. In an induction motor the rotor field runs with respect to the startor at

1. 1. synchronous speed in the same direction as the startor field

   
   
   

   2. synchronous speed in opposite direction as the startor field

   
   
   

   3. slip speed in the same direction as the startor field

   
   
   

   4. slip speed in opposite direction as the startor field.

   
   
   

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   NA

   Correct Option: A

   NA

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