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IGEE 402
– Power System Analysis
FINAL EXAMINATION  SAMPLE
Fall 2004
Special instructions:

Duration: 180 minutes.

Material allowed: a crib sheet (double sided 8.5 x 11), calculator.

Attempt 5 out of 7 questions.

Make any reasonable assumption.

All questions and subquestions carry equal weight.
QUESTION 1 (20 points)
A single phase 550 V, 60 Hz feeder supplies 2 loads in parallel: (a) a 20 kW heating load; (b) a 50
kW motor load, with an efficiency of 0.90 and a power factor of 0.80 (lagging).
(a) Draw the instantaneous current and voltage waveforms for the total load, indicating peak and
rms values. Give the equation for the total instantaneous power and draw the waveform. Indicate
the value of the total real power.
(b) Draw the VI vector diagram and the power diagram. Compute total reactive power and power
factor.
(b) A capacitor is connected in parallel with the loads to increase the power factor to 1.0. Compute
the reactive power required from the capacitor. Redraw the power diagram.
(c) Explain the benefits in having a unity power factor from (i) the utility point of view; (ii) the
consumer point of view.
QUESTION 2 (20 points)
A single phase 24 kV/2.4 kV, 60 Hz transformer, with a series equivalent impedance of 0.2 +
j
1.0
Ω
referred to the lowvoltage side, is connected at the end of a transmission line of impedance 50 +
j
400
Ω
. The transformer feeds a load drawing 200 kW, at a 0.8 power factor lagging, and 2300 V.
(a) The feeder voltage is adjusted so that the load voltage is 2300 V. Assume the load voltage has
an angle of 0 deg. Find the amplitude and angle of the voltage at the sending end of the
transmission line. (Hint: refer all quantities to the low voltage side).
(b)
Compute the current in the transmission line, the losses in the transmission line and transformer,
and the overall system efficiency.
(c)
Calculate the noload voltage and the voltage regulation.
(d)
Explain how the voltage regulation can be reduced. (Hint: consider shunt compensation).
QUESTION 3 (20 points)
A threephase feeder supplies three identical singlephase 135 kV/6.9 kV, 60 Hz, 100 MVA
transformers, each with a leakage reactance of 0.15 pu on the transformer base, and connected in a
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View Full Document IGEE 402 – Power System Analysis
– FINAL EXAMINATION – SAMPLE
Joós, G.
Page 2 of 3
∆
Y connection. The load is a threephase Yconnected 12 kV load, with per phase parameters of 60
MW, 0.85 power factor (lagging). A capacitor bank of three elements of impedance (
j
5
Ω
) connected
in
∆
is used for power factor correction. The secondary voltage is assumed to be 12 kV.
(a)
Compute the total power and total reactive power drawn from the feeder.
(b)
Draw the single line pu circuit, using a 300 MVA (threephase), 12 kV base.
(c)
Compute the total line current, the total power and total reactive power drawn from the feeder, in
pu. Compute the voltage at the feeder. Compare with results in (a).
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This note was uploaded on 09/16/2011 for the course ECSE 361 taught by Professor Franciscodgaliana during the Winter '09 term at McGill.
 Winter '09
 FRANCISCODGALIANA

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