SHORT Questions & Answers ABOUT STARTING AND SPEED CONTROL OF THREE PHASE INDUCTION MOTOR

1. State the effect of rotor resistance on starting torque.
  
Starting torque increases with in value of rotor resistance.

2. Explain why the power factor of an induction motor is very low at starting.
   
The no load power factor of an induction motor is less than 0.4 lagging. This is because the magnetizing component of no load current is higher than the loss component.

3. Define starting current.
   
Induction motors, when  direct switched take five to seven times their full load current and develop only 15. to 2.5 times their full load torque.

4 List the types of starters used in three phase induction motor.
   
Primary starters
   
Auto transformers
    Star delta starters

5. List the types of speed control schemes used in three phase induction motor.
  

Control from starter side
    Control from rotor side
    Changing applied voltage

6. What is slip power recovery scheme?
   
7. What are the advantages of star-delta starter?
  •        .cheap
  •   .starting torque is required not to be more than 1.5 times the full load torque.

8. Write the necessity of starter.
             
  Induction motors, when  direct switched take five to seven times their full load current and develop only 15. to 2.5 times their full load torque. The initial in rush of currents is controoled by applying a reduced voltage to the starter.

1.    Give the expression of synchronous speed.

    Synchronous speed : s= Ns-N/Ns

10.What is the relationship between number of poles and speed of an Induction motor?

        N = Ns(1-s)
         = 120f / p (1-s)


 Speedster/ variable Fan speed control


               
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