EE$330-$ Electromechanical Energy Conversion $($I$)$

Test no$\mathrm{.}3/$ Time: $1\mathrm{.}2$ hr

$1^{st}$ Semester $1445H$

$11$

$9$

$8$

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Ouestion $1$

$($a$)$ Can a $3$ induction motor run at synchronous speed? Explain?

$($b$)$ A $50Hz,3$ induction motor is running at a speed of $720$ rpm $.$ The input power and rotor copper loss are $9$ kW and $400$ W $,$ respectively. Find:

$($i$)$ stator copper loss $($ii$)$ speed of a stator MF $($iii$)$ rotor frequency $($iv$)$ developed torque $($v$)$ speed in rad$/$sec$.$

$($c$)$ Sketch the torque$-$speed curve of a three phase induction motor. Show the starting, maximum and load torques

Ouestion $2$

A $460V,60Hz,6-$pole, Y$-$connected $3$ induction motor has the following parameters:

$R_s=0\mathrm{.}25,R_r=0\mathrm{.}20,x_s=0\mathrm{.}5,x_r=0\mathrm{.}5,x_m=30\mathrm{.}0,P_{\text{r}\text{o}\text{t}}=1\mathrm{.}70kW.$ Determine the:

$($i$)$ developed power, supply current and power factor at starting

$($ii$)$ efficiency, developed power and output torque at a speed of $1164$ rpm