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GATE 2022 : Electrical Machine Quiz 9

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Question 1

A 3- , 400 V, 50 Hz, 4 pole, Y connected induction motor has rotor resistance of 0.3 Ω per phase and rotor reactance 0.5 Ω per phase. The value of external resistance required that should be connected in rotor circuit such that maximum torque occurs at starting?

Question 2

Consider 3-ϕ, 400V, 50Hz, 4 pole squired cage induction motor working at racked voltage and freq for same air gap flux if motor if fed from 30Hz, voltage of induction motor.

Question 3

The transformation ratio of an auto transformer for a 30 kW, 400, 3-ϕ induction motor is______. If the starting torque is to be 75% of full load torque.

Assume the full load slip to the 5% and the short circuit current to be 6 times the full load current.

Question 4

A 3-ϕ, star connected 400 V, 50 Hz, 4-pole induction motor has the following phase constants in ohms referred to stator:

R1 = 0.3 Ω, X1 = X2’ = 0.35 Ω , R2’ = 0.15 Ω, Xm = 35 Ω

Compute full load torque when motor is operated at rated voltage and frequency for a rated speed of 1440 rpm.

Question 5

A 4-pole, 50 Hz, 6 kW, 3-phase induction motor develops rated torque at 1450 rpm. In case, the load torque is reduced to one-third of original load torque by keeping voltage, frequency and other parameter constant and assuming linear torque slip characteristics, the power output will be ________.

Question 6

During the cascading connection of two induction motors, the input of second motor is  supplied through rotor output of first motor.

Motor 1 : 8 poles, Input frequency = 50 Hz

Motor 2 : 6 poles

The possible speeds are:

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Oct 20ESE & GATE EE