Question

The stator and the rotor of a 3-phase, 4-pole wound rotor induction motor are excited respectively from a 50 Hz and a 30 Hz source of appropriate voltage. Neglecting all losses, what is/are the possible no-load speed/speeds at which the motor would run?

• A. 2400 rpm only
• B. 1500 rpm and 900 rpm
• C. 2400 rpm and 600 rpm
• D. 600 rpm only

Answer 1

The correct option is C 2400 rpm and 600 rpm

$N_s\left(\text{stator field}\right)=\frac{120\times 50}{4}=1500rpm$

$N_r\left(\text{rotor field}\right)=\frac{120\times 30}{4}=900rpm$

$N_r=1500\pm 900=2400rpm,600rpm$