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# GATE EE 2021: Electrical Machine Rapid Mini Mock (App update required to attempt this test)

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Question 1

A 3-phase synchronous generator is supplying maximum power to infinite bus at rated voltage and 0.8 pu of armature current. If its excitation emf is 1.5 pu. Then the value of synchronous reactance of generator will be (Negligible armature resistance).

Question 2

A synchronous generator is connected to an infinite bus at rated voltage and the synchronous impedance is (0 + j1.8) p.u. when supplying rated current at 0.8 p.f. lagging. Keeping the emf constant, Calculate the value of load current (in p.u.) at unity power factor. (Round off the answer up to 2 decimal places)

Question 3

A 50 kW, 415 V, 3 phase, synchronous motor is operating at full load with efficiency of 90% and 0.8 lagging p.f. Determine the rating of capacitor bank to be installed at the motor terminal to raise the combined power factor 0.6 leading ______.

Question 4

A 20 kW, 6-pole, 50 Hz, 3-phase slip ring induction motor runs at 900 revolutions per minute on full load with per phase rotor current of 45 A . Allowing 400 W for the copper loss in the short circuiting gear, a 1000 W for mechanical loss. What will the resistance per phase of the three-phase rotor winding?

Question 5

A 3-phase, 10 kW, 400V, star connected alternator is supplying full load current to infinite bus at rated voltage. It has reactance of 8 Ω with negligible armature resistance. The alternator is normally excited. Then voltage regulation of alternator will be:

Question 6

A squirrel cage induction motor has a full load slip of 0.05.The motor starting torque with the help of star-delta starter is 1.5 times of full load torque. What will be the starting torque in Nm by using auto transformer starter with 60% of tapping? (Assume full load torque = 100 Nm)

Question 7

A 5KV, 25 Hz single phase transformer has copper, hysteresis, and eddy current losses of 1.4 = 0.6 and 0.5% of full load output. If the transformer is operated on 10 kV, 50 Hz supply system What Will be these losses if the current in the Winding remains same.

Question 8

The power consumption of an industry is 500 KVA, at 0.8 p.f lagging. A synchronous motor is added to raise the power factor of industry to unity. If the power intake of the motor is 150 kW, the p.f of motor will be ______.

Question 9

A 10 kW, 400V, 3-phase delta connected synchronous motor has an impedance of (0.2 + j4) Ω. The induced emf in V in motor if it takes rated current at 0.8 leading power factor. (Efficiency of motor is 90 %)

Question 10

A 220V, 8 pole, 11 kW motor has lap connected armature winding with 500 conductors. The mean flux density in the air gap under the inter poles is 0.1 wb/m2 on full load. If the radial gap length is 0.6 cm, the number of turns required on inter poles will be _________.

Question 11

A DC series motor running and have constant load torque. It is taking 30A from 200V supply at 800 rpm. Now a diverter of 0.06π is placed across the field resistance to increases the speed. Let filed flux is unsaturated, New speed in rpm.

Take field resistance = 0.05 ohm and Armature resistance = 0.01 ohm

Question 12

A 3-ϕ, salient pole synchronous generator has its reactance, Xd = 1.0 pu and Xq = 0.6 pu and Ra = 0. It is supply rated current to rated voltage at 0.8 pf lagging. Find the excitation emf in pu
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