A $3-$phase induction motor having a synchronous

speed of $1200$ rpm draws $80$ kW from a $3-$phase

feeder. The copper losses in the stator amount to $5$

kW$.$ If the motor runs at $1152$ rpm$,$ calculate:

a$)$ The active power transmitted to the rotor $($Pr$)$

b$)$ The rotor I$2$R losses $($Pjr$)$

c$)$ The mechanical power developed $($Pm$)$

d$)$ The mechanical power to drive load $($PL$)$ if the

windage and friction losses are equal to $2$ kW

e$)$ The efficiency of the motor

$[$Ans: $75$ kW$,3$ kW$,72$ kW$,70$ kW$,87\mathrm{.}5\%]$

$3$EP$3$ Fall $2021$ Lec$7$ Dr$.$ C$.$ Tang $28$