Question

A 230 V, 50 Hz, 4-pole single-phase split phase induction motor is tested to yield the following results (with auxiliary winding open):
No load test : 230 V, 6.4 A, 220 W
Block rotor test : 82.5 V, 9.3 A, 500 W
The main winding resistance is 2.5 $\Omega$, then the rotor resistance referred to stator is ________$\Omega$.

• A. 8.87 $\Omega$
• B. 3.28 $\Omega$
• C. 6.73 $\Omega$
• D. 5.78 $\Omega$

Answer 1

The correct option is B 3.28 $\Omega$

Impedance under block rotor condition,
$Z_b=\frac{V_b}{I{}_b}=\frac{82.5}{9.3}=8.87\Omega$
Resistance under block rotor condition,
$R_b=\frac{W_b}{I_b^2}=\frac{500}{(9.3{)}^2}=5.78\Omega$
Rotor resistance referred to stator,
$R_2^{\prime }=R_b-R_1$
$=5.78-2.5=3.28$ $\Omega$