18418: Electric Energy Processing: Fundamentals and Applications
Fall Semester, 2009
Homework # 4
Due on the class of September, 30
th
Problem (1)
A 150MVA 15kV/200 kV singlephase power transformer has a perunit resistance
of 1.2 percent and a per unit reactance of 5 percent (data taken from the transformer’s
nameplate). Neglect the core losses.
a)
Find the equivalent circuit referred to the lowvoltage side of this transformer.
b)
Calculate the voltage regulation of this transformer for a fullload current at power
factor of 0.8 lagging.
c)
Assume that the primary voltage of this transformer is a constant 15 kV, and plot
the secondary voltage as a function of load current for currents from noload to full
load. Repeat this process for power factors of 0.8 lagging, 1.0, and 0.8 leading.
Problem (2)
A three phase transformer connected in
Δ
Y with total power is 25kVA and per
phase voltage is 24,000/277V. The opencircuit test as performed on the lowvoltage side
of this transformer bank, and the following data were recorded:
V
line,OC
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 Fall '09
 Illic
 Threephase electric power, transformer bank, threephase power transformer, transformer’s nameplate

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