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GATE 2019: Electrical Machines Rapid Mini Mock (App update required to attempt this test)

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Question 1

A 50MVA, 10kV, 50Hz, star-connected, unloaded three-phase alternator has a synchronous reactance of 1 p.u. and a sub-transient reactance of 0.2 p.u. If a 3-phase short circuit occurs close to the generator terminals, the ratio of initial and final values of the sinusoidal component of the short circuit current is _________.

Question 2

The starting line current of a 415 V, 3-phase, delta connected induction motor is 120 A, when the rated voltage is applied to its stator winding. The starting line current at a reduced voltage of 110 V, in ampere, is ______.

Question 3

A single-phase, 2kVA, 100/200V transformer is reconnected as an auto-transformer such that its kVA rating is maximum. The new rating in kVA, is _______.

Question 4

A single-phase 400V, 50Hz transformer has an iron loss of 5000W at the rated condition. When operated at 200V, 25Hz, the iron loss is 2000W. When operated at 416V, 52Hz, the value of the hysteresis loss divided by the eddy current loss is

Question 5

A DC shunt generator delivers 45 A at a terminal voltage of 220 V. The armature and the shunt field resistance are 0.01 and 44 respectively. The stray losses are 375 W. The percentage efficiency of the DC generator is

Question 6

The following test result are obtained from a 3 phase, 5000KVA, 5500 V star connected, 2 pole 50HZ cycle turbo alternator.

With a field current of 150A, the open circuit voltage is 9000V at the rated speed, with the same field current and rated speed, the short circuit current is 900A. At the rated full load the resistance drop is 3%. ….. is the regulation of alternator on full load and at a power factor of 0.8 leading.

Question 7

A 2000KVA, star connected, 3300V, 3-phase, salient pole synchronous generator has reactance Xd= 1.5Ω and Xq= 1.2Ω per phase. The excitation for operation at rated KVA and pf of 0.8 lagging is…

Question 8

A dc series motor is running at rated speed and rated voltage. If the supply voltage has reduced to 0.5 pu then the speed should be reduced to ...... (pu)

Question 9

What is the torque developed when a of 30A passes through the armature of a motor with following parameters; 300 conductors, wave winding, 4 pole, pole shoe 17.45cm long subtending an angle of 60˚ at the centre, bore radius 17.45cm, flux density in air gap 0.6wb/m2.

Question 10

A three-phase, three winding / / Y (1.1kV/6.6kV/400 V) transformer is energized from AC mains at the 1.1 kV side. It supplies 900 kVA load at 0.8 power factor lag from the 6.6 kV winding and 300 kVA load at 0.6 power factor lag from the 400 V winding. The RMS line current in ampere drawn by the 1.1 kV winding from the mains is

Question 11

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):
Zm=(12.50+j15.75)Ω (main winding), Za=(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 ____.(round off up to one decimal places)

Question 12

A 220 V DC series motor runs drawing a current of 30 A from the supply. Armature and field circuit resistances are 0.4Ω and 0.1Ω respectively. The load torque varies as the square of the speed. The flux in the motor may be taken as being proportional to the armature current. To reduce the speed of the motor by 50% the resistance in ohms that should be added in series with the armature is _________.
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Nov 29ESE & GATE EE