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GATE 2019: Electrical Machines Quiz 7

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Question 1

Curves X and Y in Figure denote open circuit and full–load zero power factor (zpf) characteristics of asynchronous generator. Q is a point on the zpf characteristics at 1.0 p.u. voltage. The vertical distance PQ in Figure gives the voltage drop across

Question 2

A 500 MW 3-phase Y-connected synchronous generator has a rated voltage of 21.5 kV at 0.85 pf. The line current when operating at full load rated conditions will be

Question 3

A star connected synchronous motor at 100 kVA, 3-φ, 1400V, 23A, 60Hz, 126.5 rpm has an effective resistance of 0.5 ohm and a synchronous reactance of 10 ohm per phase. Determine internal power developed by the motor when it is operating at rated current and 0.5 power factor leading.

Question 4

A synchronous generator is running over excited with Ef = 1.2 pu is delivering power of 0.9 pu to the bus. Generator has synchronous reactance of 0.6 pu. Calculate the change in reactive power if prime mover torque is reduced by 1% -

Question 5

A 6 – pole, 400 V, 50 Hz, 3 – phase, synchronous motor taking a line current of 100 A at 0.8 pf leading. Assume losses are negligible Calculate the torque developed by motor –

Question 6

A lossless power system has to serve a load of 250 MW. There are two generators (G1 and G2) in the system with cost curves C1 and C2 respectively defined as follows:
C1(PG1) = PG1 + 0.055 × PG12
C2(PG2) = 3PG2 + 0.03 × PG22
Where PG1 and PG2 are the MW injections from generator G1 and G2 respectively. Then, the minimum cost dispatch will be
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Jun 19ESE & GATE EE