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GATE 2020 || Power Systems || National Champion Test (App update required to attempt this test)

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Question 1

A three phase Y-connected alternator rated as 10 MVA , 13.8 kV has following sequence reactance
Negative sequence reactance= 40%
Positive sequence reactance= 30%
Zero sequence reactance= 5%
A reactance X_n is to be added in the generator neutral such that the fault current for a line-to-ground fault of zero fault impedance will not exceed the rated line current. The per unit value of X_n is

Question 2

A synchronous generator neutral is grounded through a reactance

the generator has balanced emfs and sequence reactance

and

the value of neutral grounding reactance for which the L-G fault current is less than the three phase fault current is :

Question 3

If the size of bus admittance matrix is 90 × 90 and number of transmission lines required for system are 1575. Find the % sparsity of bus admittance matrix.

Question 4

In the single machine infinite bus system shown below, the generator is delivering the real power of 0.8 p.u. at 0.8 power factor lagging to the infinite bus. The power angle of the generator in degrees (round off to one decimal place) is ____________.

Question 5

Assume that system is operating at no load rated voltage condition prior to L-G fault at the terminal F of the generators. Find the I_F (Fault Current) and also calculate the current through the grounding resistor of 2 Ω (I_N).

Ratings for G₁ and G₂ are-

20 MVA,11Kv

X₁ = 18% X₂ = 15 % X₀ = 10 %

Question 6

A synchronous generator rated 100 kVA, 400 V, 0.1 pu. Sub transient reactance is supplying a passive load of 350 kW at 0.8 lagging power factor. If a 3-

phase fault occurs at the generator terminal, then the magnitude of initial symmetrical fault current is _____________.

Question 7

A system consisting of a generator of equivalent reactance 1.0 pu connected to an infinite bus through a series reactance of 0.6 pu. The terminal voltage of the generator (E_g) is held at 1.0 pu and the voltage of the infinite bus at 1.0 pu. The steady state limit of the system is -------- pu.

Question 8

An alternator of E = 1.2 p.u. Xg= 0.5 p.u. is connected to an infinite bus (V=1p.u.) power delivered by alternator to infinite bus is 1 p.u. if the steam input (mechanical input power) to suddenly raised to 1.5 p.u. such that system remains in stable mode. What is rotor angle change?

Question 9

In a two bus ac system, the sending end voltage |V_S| and the receiving end voltage |V_r| for the line is 1 pu. The line reactance is j0.05 pu and resistance is neglected. If the real power flow through the line is 10 pu then the reactive power flow through the line is -------p.u.

Question 10

The zero sequence reactance of each generator is 5% and that of other components are shown, the equivalent zero sequence reactance between fault point F and Ground is (upto three decimals)

Question 11

A 60 Hz generator, connected directly to an infinite bus operating at a voltage of 1 pu has a synchronous reactance of 1.35 pu. The generator no load voltage is 1.1 pu and the inertia constant H is 4MJ/MVA. The generator is suddenly loaded to 60 percent of its maximum power limit, determine the frequency of the resulting natural oscillations of the generator rotor.

Question 12

Calculate the time of operation of an IDMT type over-current relay is used to protect a feeder through 400/1 ACT, relay has plug setting of 125٪ and TMS=0 .6 and fault current is 4000A . Use the following characteristic.

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ESE & GATE EE Power Systems

Apr 20ESE & GATE EE