Chapter 6, Problem 6.20P

A three-phase, 480-V, 60-Hz, 6-pole, Y-connected induction motor has its speed controlled by slip power. The circuit parameters are given: Rs=0.06 ohms, Rr=0.05 ohms, Xs=0.2 ohms, Xr=0.3 ohms and Xm=6 ohms. The turn ratio of the rotor to stator winding is n=0.8. The no-load losses of the motor are equal to 150 W. The rotor and stator cupper losses are equal to 249.21 W. The slip power losses are estimated to 8000W. The load torque is 173.61 N.m. at 700 rpm. The efficiency is equal to: Select one: a. 71.5% b. None of these c. 81.5% d. 91.5%

Question 1: A 3 phase, 10 kW, 1700 rpm, Y- connected 460 V, 60 Hz, 4 poles, Y-connected induction motor has the following parameters: Rr = 0.2 ohms, Xs = 0.8 ohms, Xr = 0.8 ohms, Xm = 20 ohms. The no load losses are neglected. The rotor speed is assumed to be constant equal to 1700 rpm. The V/F control method is applied. The stator resistance is negligible. If the base synchronous speed is 188.5 rad/s and the voltage frequency ratio is 1.405, then the maximum torque Tm and the corresponding speed w at 30 Hz are equal to: Select one: a. 350 N.m and 70.69 rad/s b. None of these c. 350 N.m and 164.94 rad/s d. 700 N.m and 164.94 rad/s Question 2: A 3 phase, 10 kW, 1750 rpm, Y- connected 460 V, 60 Hz, 4 poles, Y-connected induction motor has the following parameters: Rs = 0.5 Ohms, Rr = 0.3 Ohms, Xs = 0.9 Ohms, Xr = 0.9 Ohms, Xm = 25 Ohms. The no load losses are neglected. In this type of control the developed torque is proportional to the square of the statoric voltage. In this part, the…

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