JNTU
JNTU B.Tech III POWER SYSTEMS ANALYSIS Previous Question Paper (March - 2024 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
PART A
Answer all questions. (25 Marks)
What are the elements of Ybus represent?
Answer
The elements of the Ybus (bus admittance matrix) represent the electrical characteristics of the power system network as follows:
1. Diagonal elements (Yii): Represent the self-admittance of bus i, calculated as the sum of all admittances connected directly to bus i, including shunt elements.
2. Off-diagonal elements (Yij): Represent the negative of the mutual admittance between bus i and bus j, which is the negative of the sum of all admittances connected in parallel between these two buses.
How the Zbus is modified when a branch of impedance Zb is added from a new bus-p to the reference bus?
Answer
When a new bus p is added to the reference bus (bus 0) through an impedance Zb, the existing bus impedance matrix Zbus is modified by adding a new row and a new column. Since the new bus is connected directly to the reference bus, the new impedance Zb becomes the diagonal element Zpp of the new row and column.
The updated matrix Zbusnew is constructed as follows:
[ 0 Zb ]
In this configuration, all off-diagonal elements in the new row and column are zero because the new bus is not connected to any of the existing buses, only to the reference bus.
Name the 3 categories of buses.
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What is meant by acceleration factor in load flow solution? What is its best value?
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What is Jacobean matrix? How the elements of Jacobean matrix are determined?
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What are the assumptions are considered for decoupled load flow method?
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What is the reactance diagram and give its applications?
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What is the order of severity and occurrence of different types of faults?
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What is the concept of equal area criterion for SMIB system?
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List three factors which affect steady state stability limit.
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PART B
(50 Marks)
What is meant by a primitive network? Give the representation of a network component in admittance form.
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By singular transformation of primitive admittance matrix y, prove that bus admittance matrix, Ybus = AT[y]A.
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Using the method of building algorithm, find the bus impedance matrix for the network shown in figure 1.
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Explain the importance of load flow studies.
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Derive the basic equations for the load flow study using Gauss-Seidal method. With respect to this method, explain the following: (i) acceleration factor, (ii) convergence criteria and (iii) Handling of PV buses.
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Three bus power system given in figure 2. Bus (1) slack bus, Vspec = 1.05∠0°. Bus (2) PV bus Vspec = 1.0 p.u, PG = 3 p.u. Bus (3) PQ bus PL = 4 p.u, QL = 2p.u. Carry out one iteration of load flow solution by Newton- Raphson method.
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Compare the Newton-Raphson method, decoupled load flow method and fast decoupled load flow method.
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Give an algorithm for decoupled load flow studies.
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Derive the expressions for DC load flow method. Also write its solution algorithm.
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Write the advantages and disadvantages of per unit system.
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The short circuit MVA at the bus bars for plant A is 1200 MVA and another plant B is 1000 MVA at 33 kV. If these two are to be interconnected by a tie-line with reactance 1.2 ohms. Determine the possible short circuit MVA at both the plants.
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What are symmetrical components? Explain.
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An earth fault occurs on one conductor of a 3-conductor cable supplied by a 10 MVA, 3-phase alternator with neutral earthed. The alternator has positive, negative and zero sequence impedances of (0.5 + j4.7), (0.2 + j0.6) and j0.43 Ω per phase. The corresponding line to neutral values for the cable upto the fault position are (0.36+j0.25), (0.36+j0.25) and (2.9 + j0.95) Ω. Find i) Fault current, ii) The sequence components in each line and iii) The voltage of the other lines to each at the fault. The generator is excited to give 6.6 kV between lines on open circuit.
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Derive swing equation for a single machine connected to infinite bus system. State the assumptions if any and state the usefulness of this equation.
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Considered the system shown in figure 3. X'd = 0.25 p.u, E = 1.25 p.u and V = 1.0 p.u; X1 = X2 = 0.4 p.u. Initially the system is operating stable while delivering a load of 1.25 p.u. Determine the stability of the system when one of the lines is switched off due to a fault.
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Discuss the methods by which the transient stability can be improved.
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Explain the solution of swing equation by point-by-point method.
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