Question

A 10-hp, 230 V, 60 Hz, three-phase, Y-connected synchronous motor drives full load at a power factor of 0.707 leading. The synchronous impedance of the motor is $j5\Omega /phase$. The rotational loss is 230 W and field winding loss is 70 W. The efficiency of the motor is______ %. (Assume 1 hp = 746 W)

• A. 96.1

Answer 1

The correct option is A 96.1
$\text{The power output,}{P}_0=10\times 746=7460W$

$\text{The power developed,}{P}_d=P_0+P_r=7460+230=7690W$

$\text{Total power input}:P_{in}=7690+70=7760W$

$\text{Efficiency},\eta =\frac{P_{output}}{P_{input}}=\frac{7460}{7760}=0.961\left(or\right)=96.1\%$