1
Problem Set #5 Y
BUS
and Z
BUS
models and power flow basics
51
(Keyhani Lecture)
The oneline diagram of an unloaded power system is shown below. Reactances of the
two sections of transmission line are shown on the diagram. The generator and
transformer ratings are as follows:
a)
Draw the per unit equivalent circuit with all reactances marked in per unit on your
circuit. Choose MVA base of 100.
b)
Compute the Y
BUS
model of the system for shortcircuit studies.
c)
Compute the short circuit current flowing through breaker A for a threephase
fault at point B.
d)
Compute the Y
BUS
model of the system for power flow studies.
52
(Keyhani Lecture)
Consider a system with the oneline diagram shown below. The threephase transformer
nameplate ratings are listed. The transformer reactances are given in percent: 10% = 0.1
p.u. The transmission line and load impedances are in actual ohms. The generator
terminal voltage (magnitude) is 13.2 kV (lineline). Find the generator current, the
transmissionline current, the load current, the load voltage, and the power delivered to
the load. Assume S
b
=10 MVA.
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 Fall '07
 Keyhani
 Alternating Current, Electric power transmission, Electricity distribution, Mains electricity

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