Load Flow Studies Practice Questions

The three-bus power system shown in the figure has one alternator connected to bus 2 which supplies $200 \mathrm{MW}$ and $40 MVAR$ power. Bus 3 is infinite bus having a voltage of magnitude $\left|\mathrm{V}_{3}\right|=1.0$ p.u. and angle of $-15^{\circ}$ . A variable current source, $|1| \angle \phi$ is connected at bus 1 and controlled such that the magnitude of the bus 1 voltage is maintained at 1.05 p.u. and the phase angle of the source current, $\phi=\theta_{1} \pm \frac{\pi}{2}$ , where $\theta_{1}$ is the phase angle of the bus 1 voltage. The three buses can be categorized for load flow analysis as

Suppose $I_{A},\:I_{B}$ and $I_{C}$ are a set of unbalanced current phasors in a three-phase system. The phase-B zero-sequence current $I_{B0}=0.1\angle 0^{\circ}$ p.u. If phase-A current $I_{A}=1.1\angle 0^{\circ}$ p.u and phase-C current $I_{C}=\left ( 1\angle 120^{\circ}+0.1 \right )$ p.u, then $I_{B}$ in p.u is

A 3-Bus network is shown. Consider generators as ideal voltage sources. If rows $1,\:2$ and $3$ of the $Y_{Bus}$ matrix correspond to Bus $1,\:2$ and $3$ , respectively, then $Y_{Bus}$ of the network is

Consider a power system consisting of N number of buses. Buses in this power system are categorized into slack bus, PV buses and PQ buses for load flow study. The number of PQ buses is $N_{L}$ . The balanced Newton-Raphson method is used to carry out load flow study in polar form. $\text{H, S, M, and R}$ are sub-matrices of the Jacobian matrix J as shown below:

The dimension of the sub-matrix M is

Bus 1 with voltage magnitude $V_1 = 1.1 p.u.$ is sending reactive power $Q_{12}$ towards bus 2 with voltage magnitude $V_2 = 1 p.u.$ through a lossless transmission line of reactance X. Keeping the voltage at bus 2 fixed at 1 p.u., magnitude of voltage at bus 1 is changed, so that the reactive power $Q_{12}$ sent from bus 1 is increased by 20%. Real power flow through the line under both the conditions is zero. The new value of the voltage magnitude, $V_1$ , in p.u. (rounded off to 2 decimal places) at bus 1 is _______ .

Out of the following options, the most relevant information needed to specify the real power (P) at the PV buses in a load flow analysis is

The $Y_{bus}$ matrix of a two-bus power system having two identical parallel lines connected between them in pu is given as

The magnitude of the series reactance of each line in pu (round off up to one decimal place) is ___________

The per-unit power output of a salient-pole generator which is connected to an infinite bus, is given by the expression, $P= 1.4 \sin\delta + 0.15 \sin 2 \delta$ , where $\delta$ is the load angle. Newton-Raphson method is used to calculate the value of $\delta$ for P = 0.8 pu. If the initial guess is 30 $^{\circ}$ , then its value (in degree) at the end of the first iteration is

A 1000 x 1000 bus admittance matrix for an electric power system has 8000 non-zero elements. The minimum number of branches (transmission lines and transformers) in this system are _____ (up to 2 decimal places).

A 3-bus power system is shown in the figure below, where the diagonal elements of Y-bus matrix are $Y_{11}=-j12pu$ , $\; Y_{22}=-j15pu$ and $Y_{33}=-j7pu$ The per unit values of the line reactances p, q and r shown in the figure are

In a load flow problem solved by Newton-Raphson method with polar coordinates, the size of the Jacobian is 100x100. If there are 20 PV buses in addition to PQ buses and a slack bus, the total number of buses in the system is ________.

A 10-bus power system consists of four generator buses indexed as G1, G2, G3, G4 and six load buses indexed as L1, L2, L3, L4, L5, L6. The generator bus G1 is considered as slack bus, and the load buses L3 and L4 are voltage controlled buses. The generator at bus G2 cannot supply the required reactive power demand, and hence it is operating at its maximum reactive power limit. The number of non-linear equations required for solving the load flow problem using Newton-Raphson method in polar form is _______.

The bus admittance matrix for a power system network is

pu There is a transmission line, connected between buses 1 and 3, which is represented by the circuit shown in figure. If this transmission line is removed from service, What is the modified bus admittance matrix?

The figure show the per-phase representation of a phase-shifting transformer connected between buses 1 and 2, where $\alpha$ is a complex number with non-zero real and imaginary parts. For the given circuit, $Y_{bus}\; and \; Z_{bus}$ are bus admittance matrix and bus impedance matrix, respectively, each of size 2x2. Which one of the following statements is true?

In a 100 bus power system, there are 10 generators. In a particular iteration of Newton Raphson load flow technique (in polar coordinates), two of the PV buses are converted to PQ type. In this iteration,

A power system has 100 buses including 10 generator buses. For the load flow analysis using Newton-Raphson method in polar coordinates, the size of the Jacobian is

A 3-bus power system network consists of 3 transmission lines. The bus admittance matrix of the uncompensated system is

If the shunt capacitance of all transmission lines is 50% compensated, the imaginary part of the $3_{rd}$ row $3_{rd}$ column element (in pu) of the bus admittance matrix after compensation is

Determine the correctness or otherwise of the following Assertion [a] and the Reason [r]. Assertion: Fast decoupled load flow method gives approximate load flow solution because it uses several assumptions. Reason: Accuracy depends on the power mismatch vector tolerance.

A two bus power system shown in the figure supplies load of 1.0+j0.5 p.u. The values of $V_1$ in p.u. and $\delta _2$ respectively are