# Power System Analysis BE Fifth Sem

1. What is meant by per unit quantity? Why is the per unit method
considered superior to percent method for short circuit calculations?
2. Draw a general circuit which can be used to determine the zero sequence
network of a two winding transformer. Using this circuit draw the zero
sequence network of a star – star transformer with star point grounded.
3. What is off nominal transformer ratio?
4. Write the importance of load flow, studies in power system analysis.
5. What is short circuit KVA?
6. What is the use of reactor in power system? Discuss different types of
reactors.
7. Distinguish between a balanced and unbalanced system by means of
symmetrical components of vectors.
8. Draw a diagram showing inter connection of sequence networks for a
double line fault.
9. Distinguish between transient and steady state stability of a power
system.
10. Discuss why an early fault clearing means better chances of maintaining
system stability.
PART – B (5 x 12 = 60)
11. (a) Figure shows a generator feeding two motors through transformer and
line. The rating and reactance are as follows.
Generator : 100 MVA, 11 KV, 3 PHASE, X = 20%
Transformer T1 : 3 Phase, 100 MVA, 11/132 KV, X = 5%
Transformer T2: Bank of three single phase transformers, each rated at 35
MVA,, 66/11KV, X = 4%
Motor M1 : 40MVA, 3 PHASE, 10 KV, X = 20%

Motor M2 : 60 MVA, 3 PHASE, 11 KV, X = 15%
The line reactance is 80 ohm. Select suitable base values. Draw
reactance diagram. Indicate per unit reactance in the diagram.(fig1)
(8)
(b) Explain about sequence impedances in a power system network.
(4)
(or)
12. (a) Discuss the step by step method formation of Y bus. (5)
(b) The parameters of a 4-bus system are as follows. (7)
Bus Code Line Impedance (P.U) Changing Admittance(P.U) (Ypq/2)
1-2 0.2 + j0.8 j0.02
2-3 0.3 + j0.9 j0.03
3-4 0.25 + j1 j0.04
3-4 0.2 + j0.8 j0.02
1-3 0.1 + j 0.4 j0.01
Draw the network and find bus admittance matrix.
13. (a) Give a flow chart for the load flow study on a power system having
only PQ buses using GS method. (5)
(b) A 4 buses system has the following line reactance (the resistance are
negligible).
Line Code Reactance
Bus 1-2 j0.5 pu
2-3 j 1.0pu
3-4 j11.0pu
1-4 j 0.5pu
The Bus specification and values of injected powers are as under
Bus P Q V Bus Specifications
1 – – 1.05 pu Slack
2 -0.1 pu Zero – Load bus
3 0.5 pu 0.02pu – Generator bus
4 -0.4 pu -0.05 pu – Load bus
Use G-S method and find values of V2, V3 & V4 after one iteration.

Equipment MVA rating Voltage rating XI X2 X0
G1 100 11KV 0.25 0.25 0.05
G2 100 11KV 0.2 0.2 0.05
T1 100 11/220KV 0.06 0.06 0.06
T2 100 11/220KV 0.07 0.07 0.07
Line 1 100 220KV 0.1 0.1 0.3
Line 2 100 220KV 0.1 0.1 0.3
(or)
18. A 25 MVA, 11 KV, 3 phase synchronous generator with solidly grounded
neutral has sub transient reactance of 0.25pu. The –ve and zero sequence
reactances are 0.35pu and 0.1 pu respectively. Determine the generator
and line to line voltage when a single line to ground fault occurs at the
terminals of an unloaded generator operating at rated voltage. Resistance
may be neglected.
19. (a) Explain clearly the application of equal area criterion for studying the
transient stability of a power system. (5)
(b) The steady state limit of a power system is 100MW. A generator with
constant excitation is supplying 50MW to the system. Estimate the
maximum permissible sudden increase in generator output without
causing instability. (7)
(or)
20. (a) What is meant by “Power – angle” diagram? Show how this may be
used to determine the stability of a simple system under a transient fault
condition. (5)
(b) A 50 Hz turbo generator in delivering 50% of power that is capable of
delivering through a transmission line to an infinite bus. A fault occurs
that increases the reactance between generator and infinite bus to 400% of
the value before the fault. When the fault is isolate, the maximum power
that can be delivered is 75% of the original maximum value. Determine
critical clearing angle for the conditions given above.