Question

A 220 V, single-phase induction motor gave the following test results:
Blocked rotor test : 120 V, 9.6 A, 460 W
No load test : 220 V, 4.6 A, 125 W
The stator winding resistance is $1.5\Omega$ and during the blocked rotor test, the starting winding is open. The core friction and windage losses will be ______W.

• A. 125.50 W
• B. 25.02 W
• C. 74.80 W
• D. 50.70 W

Answer 1

The correct option is C 74.80 W

$V_{sc}=120V,I_{sc}=9.6A,P_{sc}=460W$

$Z_e=\frac{V_{sc}}{I_{sc}}=\frac{120}{9.6}=12.5\Omega$

$R_e=\frac{P_{sc}}{I_{sc}^2}=\frac{460}{(9.6{)}^2}=4.99\Omega$

$R_s=1.5\Omega$

$R_2^{\prime }=R_e-R_s=4.99-1.5=3.49\Omega$

$\text{Given,}$ $V_0=220V,I_0=4.6A,P_0=125W$

$\text{Core, friction and windage losses}$
$=125-(4.6{)}^2(1.5+\frac{3.49}{4})=74.8W$