$6\mathrm{.}51$ A $440$ V$,$ Hz$,4$ pole, $1420$ rpm$,$ delta$-$connected squirrel$-$cage induction motor has the following parameters: R$,=0\mathrm{.}3582,$ R $=0\mathrm{.}482,$ X$,=0\mathrm{.}79,$ X; $=0\mathrm{.}882$ RR The motor is fed from a voltage source inverter. The drive is operated with a constant $($VIF$)$ control up to $50$ Hz and at rated voltage above $50$ Hz$.1($i$)$ Calculate the breakdown torques for a frequency of $75.$ Hz both 'for motoring and braking operations. $($ii$)$ Frequency for motoring operation at $950$ rpm and full$-$load torque. $($iii$)$ Frequency for the regenerative braking operation at $1000$ rpm and full$-$load torque. Assume speed$-$Loruqe curves to be parallel straight lines in the region of interest.