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GATE 2022 : Electrical Machine Quiz 10

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Question 1

A cascade induction motor set consists of two machines; the main motor has 4 poles and  the auxiliary motor has 6 poles. Find the possible synchronous speed obtained at 50Hz  supply.

Question 2

In 3-phase squirrel cage induction motor, for low value of slip: (symbols have their usual meaning).

Question 3

A 4 pole, 8 kW, 50 Hz, 3-phase Induction motor develops rated torque at 1440 rpm. In case load torque is reduced to one-fourth (of rated). The power output will be ________kW. (Assume linear torque slip characteristic near the operation range).

Question 4

A , 6-pole 50 Hz, 400 V, connected induction motor develops a maximum torque at a speed of 800 rpm, stator impedance and rotational losses are assumed to be negligible, the rotor resistance is 0.15 Ω/phase. Calculate the additional resistance in the rotor circuit to be connected to attained 60% of maximum torque at starting when supply voltage is reduced to 350 V.

Question 5

A three-phase, squirrel-case induction motor is developing torque of 1500 sync. Watts at 50 Hz and 1400 rpm (synchronous speed is 1500 rpm). If the motor frequency is now increased to 75 Hz using constant power mode, what is the new value of torque developed by the motor at constant slip?

Question 6

Consider a 4-pole, 50 Hz, 3-phase Induction motor that is running at 1440 rpm. Its developing output is 15 kW. The efficiency is _______. (Take mechanical loss = 1.25 kW and stator loss = 0.75 kW).
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