# Sathyabama University Exam Papers BE

# Power system Analysis Fifth Sem

Answer ALL the Questions

1. Define per unit value of any quantity.

2. A generator is rated 500MVA, 22kV. It star connected windings have

a reactance of 1.1 pu. Find the ohmic value of reactance of the

winding.

3. Zbus of the partial network is available. To this a new branch is added.

Write down the expression for the modified Zbus.

4. Write Y pr in terms of incidence matrix.

5. The typical power system has symmetrical short circuit current Isc.

Write the expression for momentary fault current.

6. What is the purpose of symmetrical components?

7. What do you mean by the term bus switching?

8. Define mismatch.

9. On what factors does the stability of the system depend?

10. Distinguish steady state and transient stability.

PART – B (5 x 12 = 60)

Answer All the Questions

11. (a) A 3 f transformer is rated 400MVA, 220Y/22D. The Y-equivalent

short circuit impedance measured on the L.V. side of the transformer

is 0.121 W. Determine the p.u reactance of the transformer and p.u

value to be used to represent this transformer in a system whose base

on H.T. side of the transformer is 100 MVA, 230KV.

(b) What is the need for system analysis in planning and operation of

power system? Explain.

(or)

12. (a) Explain the modeling of generator, load, shunt capacitor and

transmission line for short circuit studies.

(b) The single line diagram of an unloaded power system is shown in

figure. The reactance of the two section of the transmission lines are

shown in the diagram. The generators and transformers are rated as

follows:

G1: 20 MVA, 13.8 kV, Xd = j0.2pu.

G2: 30 MVA, 18 kV, Xd = j0.2pu

T1: 25 MVA, 3 phase, 220 Y/13.8 DkV, X=10%

T2: 3, single Phase units, each rated 10MVA, 127Y/18D kV

X= 10%

13. The reactance data in pu for a sample system is given in the table.

Draw the single line diagram representing the system. Obtain Ybus

matrix by singular transformation method.

Line X in pu

1.2 j 0.04

2.5 j 0.05

5-4 j 0.04

4-3 j 0.03

3-6 j 0.02

6-1 j 0.07

3-1 j 0.10

(or)

14. For the network shown in fugure, impedance labeled through 1 to 6

are in p.u. Formulate Zbus using building algorithm.

17. Discuss the importance of load flow problem. Formulate the load

flow problem and describe the procedure of solving it using Newton

Raphson method.

(or)

18. Consider a 3 bus system shown in figure 2. The details of line

admittances, bus voltages and bus powers are given in table. Perform

one iteration of Gauss-Seidel method.

Table 1:

Table 2:

Bus

No

Bus

Voltages

PD QD PG QG

1 1.05+j0 0 0 — —

2 1.0+j0 50 20 20 0

3 1.0+j0 60 25 0 0

19. Explain the algorithm for transient stability simulation using

modified Eulers method.

(or)

20. (a) Describe in brief about the Equal area criterion

(b) A generator operating at 50 Hz delivers rated power to an infinite

bus. Power to an infinite bys when a fault occurs reduces and it is 0.4

p.u. The maximum power transferred during prefault os 1.75. the

maximum power transferred during post fault is 1.25. Compute

critical clearing angle.

Bus Code Impedances

1-2 0.08+j0.24

1-3 0.02+j0.06

2-3 0.06+j0.18