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# GATE 2022: Electrical Machine-44 (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

An 8- pole, 3 - ϕ, 50 Hz induction motor runs at a speed of 710 rpm with an input power of 35 kW. The stator copper loss at this operating condition is 1200 W while the rotational losses are 600 W. Find the value of gross torque in N-m.

Question 3

A 20 kVA, single phase transformer of 1100/220 V has an iron loss of 175 W. The resistances of primary and secondary windings are respectively 0.25 ohm and 0.012 ohm. The efficiency will be maximum at what percentage of full load?

Question 4

A single phase transformer working on unity power factor has an efficiency of 0.9 p.u. both at half load and the full load. Determine the efficiency at 75% of full load.

Question 5

A 28.6 HP, 230 V d.c shunt motor with a full load speed of 434 rpm is to be braked by plugging. Estimate the value of resistance which should be placed in series with it to limit the initial current to 150 A.

Question 6

A 220 V, DC shunt motor is operating at a speed of 1440 rpm. The armature resistance is 1.0 Ω and armature current is 10 A. If the excitation of the machine is reduced by 10%, the extra resistance to be put in the armature circuit to maintain the same speed and torque will be
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