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GATE 2020: Power Systems Rapid Revision Quiz 3

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Question 1

A negative sequence relay is commonly used to protect

Question 2

A 50 Hz balanced three-phase, Y-connected supply is connected to a balanced three phase Y-connected load. If the instantaneous phase-α of the supply voltage is Vcos(ωt) and the phase-α of the load current is Icos(ωt–

), the instantaneous three-phase power is

Question 3

A 100/5 A bar primary current transformer supplies an over current relay set at 25% pickup and it has a burden of 5 VA. The knee point voltage and cross section of the core if the CT has 50 turns on its secondary and the fault current is 15 times the relay setting.
Assume the flux density as 1.4 Wb/m².

Question 4

In a 3-phase synchronous generator, the induced emf in one of the phases is 4.5 pu. If a current of 14.2 pu flows through the 0.82 pu negative sequence impedance, determine the negative sequence voltage of the phase with respect to the reference bus.

Question 5

The incremental cost (in Rupees/MWh) of operating two generating units are functions of their respective power P1 and P2 in MW, and are given by

;

Where

, and

. For a certain load demand, P₁ and P₂ have been chosen such that

and

. IF the generations are rescheduled to minimize the total cost, then P₂ is _________.

Question 6

A 50 Hz generating unit has H-constant of 2 MJ/MVA. The machine is initially operating in steady state at synchronous speed, and producing 1 pu of real power. The initial value of the rotor angle δ is 5 °, when a bolted three phase to ground short circuit fault occurs at the terminal of the generator. Assuming the input mechanical power to remain at 1 pu, the value of δ in degrees, 0.02 second after the fault is _________.

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ESE & GATE EE Power Systems

Nov 19ESE & GATE EE