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# GATE 2022: Electrical Machines-48 (App update required to attempt this test)

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Question 1

Consider a 4-pole series motor which has two cases:

Cases (I) when its two filed coils connected in parallel speed = 1000 rpm

Case (II) Field coils connected in series, keeping the supply voltage ∝ load torque same

For case (II) speed is___ rpm

Question 2

A 375 W, 230 V, 50 Hz capacitor start single-phase induction motor has the following constants for the main and auxiliary windings (at starting):

Z

Neglecting the magnetizing branch, the value of the capacitance (in μF ) to be added in series with the auxiliary winding to obtain maximum torque at starting is ____.

Z

_{m}=(12.50+j15.75)Ω (main winding), Z_{a}=(24.50+j12.75)Ω (auxiliary winding)Neglecting the magnetizing branch, the value of the capacitance (in μF ) to be added in series with the auxiliary winding to obtain maximum torque at starting is ____.

Question 3

A single-phase, 4-pole induction motor takes a line current of 60∠–70° A at stand still with its main winding excited from 230V, 50 Hz source. Neglect stator impedance, magnetizing current and rotational loss. Calculate stator current. (slip = 5%)

Question 4

Consider a 1 MVA, 11 kV, three-phase, synchronous motor. Motor armature resistance and reactance per phase are 3.5 Ω & 40 Ω, respectively. When motor is fully loaded at 0.8 power factor (leading), then the per phase induced emf is ________V.

Question 5

For a 3-phase 50 Hz 4-pole 50 KW 400 V, wound rotor induction motor has a maximum internal torque 4 times of full load torque. This condition occurs at 25% slip, when operated at rated voltage and frequency with its rotor short circuited directly at slip rings. If rotational losses are zero at full load, rotor copper losses will be _______ Watts.

Question 6

An auto transformer having 70% tapping, connected to 3-phase, cage induction motor. This restricts the maximum line current that is drawn from 415 V, 3-phase supply at 130 A . Then the Full load kVA of motor is ________. Take: If starting current is 5 times the Full load current.

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Jun 17ESE & GATE EE

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