156. In Machine tool drive application, the speed of separately excited dc moter is required to be controlled both below and above the rated speed of the motor. Which one of the followinjg methods is best suited for this purpose? (V_a = armature voltage, I_f = field current and Ifrated = field current at rated speed)
     

1. 1. I_f = I_frated, V_a variable

   
   
   

   2. V_a fixed, I_f variable
      

   
   
   

   3. V_a and I_f variable, with I_{f ≤ Ifrated}
      

   
   
   

   4. V_a and I_f variable with I_{f ≥ Ifrated}

   
   
   

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   NA

   Correct Option: C

   NA

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157. For the switching waveform shown in fig. for a power transistor the peak instantaneous power loss in watts is—
     
     
     
     

1. 1. 250
      

   
   
   

   2. 500
      

   
   
   

   3. 166·67
      

   
   
   

   4. 333·33

   
   
   

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   NA

   Correct Option: A

   NA

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158. A single-phase voltage Source square-wave inverter feeds pure Inductive load. The wave form of the load current will be—
     

1. 1. Sinusoidal
      

   
   
   

   2. Rectangular
      

   
   
   

   3. Trapezoidal
      

   
   
   

   4. Triangular

   
   
   

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   NA

   Correct Option: D

   NA

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159. An MCT has three terminals called—
     

1. 1. Collector, emitter and gate
      

   
   
   

   2. Anode, cathode and gate
      

   
   
   

   3. Drain, source and base
      

   
   
   

   4. Drain, source and gate

   
   
   

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   NA

   Correct Option: B

   NA

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160. An IGBT has three terminals called—
     

1. 1. Collector, emitter and base
      

   
   
   

   2. Drain, source and base
      

   
   
   

   3. Drain, source and gate
      

   
   
   

   4. Drain, source and gate

   
   
   

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   NA

   Correct Option: D

   NA

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