Which of following methods are suitable for the speed control of squirrel cage induction motor? 1. Voltage control. 2. Frequency control. 3. Pole changing method. 4. Rotor resistance control select the correct answer using the codes given below:-

• A.  2, 3 and 4.
• B.  2 and 4.
• C.  1, 3 and 4.
• D.   1, 2 and 3.

Answer: (D)