# Sathyabama Uni Previous Year Question Paper Power system Analysis

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)
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.

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