GATE 2020 || Electrical Machines || Quiz 7

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Question 1

A single phase, 2000 V alternator has armauture resistance and reactance of 0.8 and 4.94 respectively. The voltage regulation of the alternator at 100 A load at 0.8 leading power factor is –x% then x is________.

• A8.5
• B8.9
• C8.10
• DNone of these

Question 2

A hydraulic turbine having rated speed of 250 rpm is connected to a synchronous generator. In order to produce power at 50 Hz, the number of poles required in the generator are

• A6
• B12
• C16
• D24

Question 3

A 400 V, 3-φ, 50 Hz star connected synchronous motor has a rated armature current of 25 A. The armature resistance is negligible X_d = 5 Ω/ph; X_q = 3.2 Ω/ph. If the input is 10 kW, determine the power angle δ for excitation voltage of 420 V.

• A38.52 °
• B40.52 °
• C42.52 °
• D44.52 °

Question 4

A 1000 KVA, 66 kV, star connected alternator has a resistance of 1 Ω and a synchronous reactance of 10 Ω/ph. The machine delivers a load of 600 kW at 0.6 pf lagging. What is the emf generated in the armature?

• A38180 V
• B37170 V
• C36160 V
• D35150 V

Question 5

A three-phase, 50Hz salient-pole synchronous motor has a per-phase direct-axis reactance (X_d ) of 0.8pu and a per-phase quadrature-axis reactance (X_q) of 0.6pu. Resistance of the machine is negligible. It is drawing full-load current at 0.8pf (leading). When the terminal voltage is 1pu, per-phase induced voltage, in pu, is

• A1.608
• B2.213
• C5.232
• D6.453

Question 6

A 1000 kW, 3, Y connected, 3.3 kV, 24-pole, 50 Hz synchronous motor has asynchronous reactance of 3.24/ph; the resistance being negligible. The motor is fed frpom infinite bus-bars at 3.3 kV. Its field excitation is adjusted to result in unity p.f. operation at rated load. Compute the maximum power that the motor can deliver with its Excitation remaining constant at this value.

• A3405 kW
• B3505 kW
• C3605 kW
• D3705 kW

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