JNTU
JNTU B.Tech III POWER SYSTEMS ANALYSIS Previous Question Paper (November/December - 2020 - R16)
Answer any five questions. All questions carry equal marks.
Main
How do you obtain an element –node incidence matrix from a given network.
Answer
The element-node incidence matrix, denoted as A, describes the connectivity of a network by relating elements to nodes. To construct it for a network with e elements and n nodes:
- Assign a reference node (usually ground) which is excluded from the matrix, resulting in a matrix of size e x (n-1).
- Assign an arbitrary direction to each element (from bus p to bus q).
- Fill the matrix entries Aij as follows:
- Aij = 1 if element i is incident to and leaves node j.
- Aij = -1 if element i is incident to and enters node j.
- Aij = 0 if element i is not connected to node j.
For the power system network shown below figure 1, the primitive data is as given in below Table. Compute the Ybus matrix by taking a mutual coupling of 0.2 between the elements 4 and 5.
| Element Number | From Bus | To Bus | Primitive Impedance |
|---|---|---|---|
| 1 | 1 | 0 | 0.05 |
| 2 | 3 | 0 | 0.10 |
| 3 | 1 | 2 | 0.50 |
| 4 | 2 | 3 | 0.40 |
| 5 | 1 | 3 | 0.25 |
Answer
First, convert primitive impedances to admittances (y = 1/z): y1=20, y2=10, y3=2, y4=2.5, y5=4. The mutual coupling between elements 4 and 5 (zm = j0.2) implies a mutual admittance ym = -y4y5zm = -(2.5)(4)(j0.2) = -j2. The primitive admittance matrix Yp is diagonal except for the coupling between elements 4 and 5. The bus incidence matrix A (nodes 1, 2, 3) is:
The Ybus is computed using Ybus = AT Yp A. Calculating the product yields:
Incorporating the mutual coupling ym into the nodal equations adjusts the off-diagonal elements connected to the mutually coupled buses. The final Ybus matrix is obtained by summing the direct admittances and the contribution of the mutual coupling term.
Discuss in detail about the formation of Z bus.
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With an example, Discuss about singular transformation method.
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Discuss in detail about Bus classification in power flow studies.
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Explain in detail about Gauss-Seidel method in complex form without voltage control buses.
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What are the Jacobian elements? Explain in detail about their significance.
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Figure 2 below shows a two-bus DC power system connected by a transmission line whose resistance R = 0.05 per unit. The load P on bus 2 is 1.0 per unit. Write the load flow equation and solve it by Newton-Raphson method to obtain the voltage at bus 2. Assume bus 1 as the slack bus having a voltage of 1.0 per unit. Take tolerance limit for convergence equal to 0.001. Determine the power supplied by the slack bus.
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Explain in detail about decoupled sub matrices of J-matrix.
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With the help of an example, Explain about decoupled load flow method.
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Explain the assumptions of fast decoupled load flow method.
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What is a DC load flow method? Explain.
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Explain in detail about the fault calculation of LLG fault without fault impedance.
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What is a series reactor? Explain its applications.
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Discuss about power angle equation with and without neglecting line resistance.
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What is critical clearing angle? Explain its significance in detail.
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