Question

A three-phase, 50 Hz, 6-pole induction motor runs at 960 rpm. The stator copper loss, core loss, and the rotational loss of the motor can be neglected. The percentage efficiency of the motor is:

• A. \( 92 \)
• B. \( 94 \)
• C. \( 96 \)
• D. \( 98 \)

Hint:

Efficiency of induction motors can be approximated using \( \eta = 1 - \text{slip} \) when losses are negligible.

Answer 1

The Correct Option is C

Step 1: Calculating synchronous speed. The synchronous speed is: \[ N_s = \frac{120 f}{P} = \frac{120 \times 50}{6} = 1000 \, \text{rpm}. \] Step 2: Calculating slip. \[ \text{Slip} (s) = \frac{N_s - N_r}{N_s} = \frac{1000 - 960}{1000} = 0.04. \] Step 3: Calculating efficiency. Efficiency (\( \eta \)) is given by: \[ \eta = 1 - s = 1 - 0.04 = 0.96 \, \text{or } 96\%. \] Hence, the correct option is (3) \( 96 \).