Question Bank for Computer Aided Power System Analysis.

Page: 01

  1. What are the different approaches of AC-DC load flow? Discuss any one of them in detail.

2. Why YBUS formulation is preferred over ZBUS in power flow algorithms ? State the advantages of YBUS matrix.

3. Develop the detailed YBUS matrix formulation considering mutual coupling between transmission lines.

4. What are the different operating states of a power system ? Discuss them in detail alongside the state transition diagram.

5. What does contingency analysis mean in the power system ? Why is it essential for the power system planning? Explain with the help of an example.

6. How Dynamic Programming (DP) can be used to evaluate the Unit Commitment (UC) Table ? Use DP to obtain the UC table for the system shown in Table 1.

Unit No.Capacity (MW)
Min.		Capacity (MW)
Max.		Cost curve parameters (d=0)
a (Rs./MW2)		Cost curve parameters (d=0)
b(Rs/MW)
11120.7723.5
21121.6026.5
31122.0030.0
41122.5032.0
Table: 1 (Generating unit parameters for the sample system)

7. Consider the following incremental cost curves in Rs./MWh for a plant having two units

\[\color\red{\dfrac{dC_1}{dPG_1}\; =\; 0.20PG_1 \;+\; 40}\] \[\color\red{\dfrac{dC2}{dPG_2}\; =\; 0.12PG_2 \;+\; 15}\]

Calculate the extra cost incurred is Rs./h, if a load of 220MW is scheduled as PG1 =
PG2 = 110MW.

8. Obtain the graph for the power system network shown in Figure 1. Draw possible trees and co-trees for the obtained graph. Also, obtain the bus incidence matrix (A) by taking ground as a reference. Assume that all lines are modelled as a π network.

Figure 1: 4-Bus Power System Network

9. Consider the 3–bus system as shown in the Figure 2. The per–unit (p.u.) line reactances
are indicated on the figure, assuming that line resistances are negligible. The magnitude
of all abuse voltages are specified to be 1.0 p.u. The power is specified in the Table 2.
Carry out the complete approximate load flow solution. Mark generations, load demands,
and line flows on the one-line diagram.

Figure 2: Line Configuration of 3-Bus Power System
BusReal DemandReactive DemandReal GenerationReactive Generation
1PD1 = 1.0QD1 = 0.6PG1 =?QG1(unspecified)
2PD2 = 0.0QD2 = 0.0PG2 = 1.4QG2(unspecified)
3PD3 = 1.0QD3 = 1.0PG3 = 0.0QG3(unspecified)
Table 2: 3-Bus Load and Generation Data

10. Develop the π model for a transformer (whose transformation ratio is 1 : a) connected
between bus i and bus j.

11. Use singular transformation approach to obtain the bus admittance matrix (Ybus) for the
power system network shown in Table 3. Show all steps.

From BusTo BusReactance (p.u.)Half Line Charging (susceptance in p.u.)
120.2000.24
230.1000.16
340.2500.30
410.1250.50
130.1250.50
Table 3: 4-Bus Power System Line Data

12. Utilise an appropriate method to obtain the power flow solution (for the first iteration)
for the network shown in Table 1. The bus data is displayed in Table 4 if needed.

BusVoltage Mag. (pu)Voltage Angle (Deg.)Real Power (pu)Reactive Power (pu)
11.060……
2……0.200.10
3……0.450.15
4……0.600.10
Table 4: Bus Data

13. Write the computer algorithm to obtain the power flow solution using the Gauss-Seidel
method. Derive the basic voltage equation used in this method.

14. What are the different operating states of a power system? Discuss them in detail
alongside the state transition diagram.

15. What does contingency analysis mean in the power system ? Why is it essential for the
power system planning ? Explain with the help of an example.

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