National Champion Test -GATE 2018 EE: Power System for ESE & GATE EE Exams

Question 1

A 230 V (Phase). 50 Hz, three-phase 4-wire system has a phase sequence ABC. A unity power-factor load of 4 kW is connected between phase A and neutral N. It is desired to achieve zero neutral current through the use of a pure inductor and a pure capacitor in the other two phases. The value of inductor and capacitor is

Question 2

A power system consists of 300 buses out of which 20 buses are generator buses, 25 buses are the ones with reactive power support and 15 buses are the ones with fixed shunt capacitors. All the other buses are load buses. It is proposed to perform a load flow analysis for the system using Newton–Raphson method. The size of the Newton–Raphson Jacobian matrix is

Question 3

Consider a power system shown below:

Given that:
V_s1 = V_s2 = 1.0 + j0.0 pu;
The positive sequence impedances are Z_s1 = Z_s2 = 0.001 + j0.01 pu and Z_L = 0.006 + j0.06 pu.
3-phase Base MVA = 100
Voltage base = 400 kV (Line to Line)
Nominal system frequency = 50 Hz
The reference voltage for phase ‘a’ is defined as v (t) = V_m cos (ωt).
A symmetrical three phase fault occurs at centre of the line, i.e. point ‘F’ at time t₀. The positive sequence impedance from source S₁ to point ‘F’ equals 0.004 + j0.04 pu. The waveform corresponding to phase ‘a’ fault current from bus X reveals that decaying dc offset current is negative and in magnitude at its maximum initial value. Assume that the negative sequence impedances are equal to positive sequence impedances, and the zero sequence impedances are three times positive sequence impedances.
The instant (t₀) in mili second of the fault will be

Question 4

The figure shows a two-generator system supplying a load of P_D = 40 MW, connected at bus 2.

The fuel cost of generators G₁ and G₂ are:
C ₁ = 10,000 Rs / MWh and C₂ = 12,500 Rs/MWh and the loss in the line is P_Loss_(pu) = 0.5

, where the loss coefficient is specified in pu on a 100 MVA base. The most economic power generation schedule in MW is

Question 5

A cylindrical rotor generator delivers 0.5 pu power in the steady-state to an infinite bus through a transmission line of reactance 0.5 pu. The generator no-load voltage is 1.5 pu and the infinite bus voltage is 1 pu. The inertia constant of the generator is 5 MW-s/MVA and the generator reactance is 1 pu. The critical clearing angle, in degrees, for a three-phase dead short circuit fault at the generator terminal is

Question 6

Consider a synchronous generator connected to an infinite bus by two identical parallel transmission lines. The transient reactance x of the generator is 0.1 pu and the mechanical power input to it is constant at 1.0 pu. Due to some previous disturbance, the rotor angel (δ) is undergoing an undammed oscillation, with the maximum value of δ(t) equal to 130^o. One of the parallel lines trips due to relay maloperation at an instant when δ(t) = 130^O as shown in the figure. The maximum value of the per unit line reactance, x, such that the system does not lose synchronism subsequent to this tripping is

Question 7

The generalized circuit constants of a 3-phase, 220 kV rated voltage, Moderatelength transmission line are
A = D = 0.936 + j0.016 = 0.936

B = 33.5 + j138 = 142.0

C = (–5.18 + j914)

If the load at the receiving end is 50 MW at 220 kV with a power factor of 0.9 lagging, the magnitude of line to lien sending and voltage should be

Question 8

A 400 V , 50 Hz, three phase balanced source supplies power to a star connected load whose rating is

, 0.8 pf(lag), The rating (in KVAR) of the delta connected (capacitive) reactive power bank necessary to bring the pf to unity is

Question 9

The sequence components of the fault current are as follows: I_positive = j 1.5 pu, I_negative = –j 0.5 pu, I_zero = –j 1 pu. The type of fault in the system is

Question 10

Equation e^x – 1 = 0 is required to be solved using Newton’s method with an initial guess x₀ = –1. Then, after one step of Newton’s method, estimate x₁ of the solution will be given by

Question 11

High Rupturing Capacity fuses protect the circuit when it is:

Question 12

A three phase semi-converter feeds the armature of a separately excited dc motor, supplying a non-zero torque. For steady state operation, the motor armature current is found to drop to zero at certain instances of time. At such instances, the voltage assumes a value that is

Question 13

A transmission line having its transmission line parameters as A = 1, B = 2, C = 0.02, D = 1. What is the Characteristic Impedance (Zc)

Question 14

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 15

If X is the inductive reactance/phase and R is the resistance/phase of a short transmission line, what is the power factor angle of the load for maximum voltage regulation?