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BARC 2018 EE: Electrical Machines Nuclear Quiz 3

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Question 1

A three-phase, 11 kV, 50 Hz, 2 poles, star connected, cylindrical rotor synchronous motor is connected to an 11 kV, 50 Hz source. Its synchronous reactance is 50Ω per phase, and its stator resistance is negligible. The motor has a constant field excitation. At a particular load torque, its stator current is 100 A at unity power factor. If the load torque is increased so that the stator current is 120 A, then the load angle (in degrees) at this load is ________.

Question 2

Which of the following type of self-excited dc motor behaves more like the separately excited dc motor?

Question 3

A 250 V shunt motor has an armature resistance of 0.5 Ω and a field resistance of 250 Ω. When driving at 600 rev/min a load, the torque of which is constant, the armature takes 20 A. If speed changes from 600 rpm to 800 rpm, what resistance must be inserted in the shunt field circuit, assuming the magnetization curve to be a straight line?

Question 4

For a 1.15 kVA 230/460V transformer connected to a standard 1 - phase 230V supply, the no load current (approx 4% of full load current) likely to be?

Question 5

A 100 kVA, 2 winding transformer has an iron loss of 1 kW and a copper loss of 1.5 kW at normal output current. Calculate maximum efficiency at 0.8 lagging power factor.
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Jun 15ESE & GATE EE