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# GATE 2022: Electrical Machines - 55

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Question 1

When a short-circuit test is conducted on a single-phase transformer, 30% of the rated voltage is required to allow full load current. The short circuit power factor is found to be 0.2. The percentage regulation at UPF is

Question 2

A 6-pole, 50 Hz, 3-phase induction motor running on full load develops a useful torque of 200 Nm at a rotor frequency of 2 Hz, the shaft power will be ______ kW.

Question 3

A 4 pole lap wound DC generator has 180 coils. The armature is 50 cm long and 30 cm diameter. Each pole subtends an angle of 75° mechanical. The air gap density is 0.5 T. Find out the flux carried by each pole.

Question 4

Two exactly similar 1000 KVA synchronous generator work is parallel. The governor of first machine is such that frequency drops uniformly from 50 Hz at no load to 48 Hz on full load. The corresponding uniform speed drop of second machine is from 50 Hz on no-load to 47 Hz at full load. The maximum load at unity power factor that can be delivered without overloading either of the two machines is _______ kW.

Question 5

A 3-phase squired cage induction motor, with an applied voltage of 50% gives a blocked rotor current of 200% and starting torque of 40% of their corresponding values. If an auto transformer limits the supply current to 180% of motor full load current, the percentage starting torque of full load torque will be:

Question 6

A 3-phase, synchronous generator has synchronous reactance of 0.5 pu and negligible resistance. It is supplying an active power of 0.9 pu at rated voltage. Its excitation emf is 1.3 pu. The reactive power output will be:

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Jun 24ESE & GATE EE

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