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EECE 581 HW #2: pf Correction & 3 circuits
1.
Given a 240 V source feeding a 100 +j 150 Ohm load, find the size of the capacitor needed
to make the new source power factor 0.9 lagging.
2.
Given a 240 V source feeding a 100 / 20° Ohm load, find the size of the capacitor needed
to make the new source power factor unity.
3.
Given a 480 V source feeding a 80 / 30° Ohm load, with a 7 F capacitor added to
improve the power factor, find the load power, the source power with and without the
capacitor, and the capacitor VARs. Also find the source current with and without the
capacitor. Explain the difference between these current values.
4.
Assume a balanced 3 load attached to balanced 3 source. If the line to neutral voltage at
the load is 120 / 15° V, find all of the line to neutral and line voltages at this load.
5.
Assume a balanced, 480 V, 3 source feeds a delta connected load with impedance of 100
+ j 75 Ω through a transmission line with impedance j5 Ω . Find all of the line voltages,
line to neutral voltages, line currents, and phase currents. Find also the three phase power
of the load, the line, and the source.
6.
Assume a balanced, 3 source feeds two loads in parallel through a line with impedance of
j5 Ω. Load 1 is at 480 V, balanced, 3, Y-connected and has an impedance of 50 + j 100
Ω. Load 2 is at 480 V, balanced 3, and takes 1000 Watts and 300 VARs. Draw the oneline diagram for this system. Find the line to neutral voltage of the source. Find the line
current produced by the source. Find the power produced by the source.
7.
Assume a balanced, 3 source feeds two loads in parallel. Load 1 is at 480 V, balanced,
3, Y-connected and has an impedance of 50 + j 100 Ω. Load 2 is at 480 V, single-phase
connected between phases A and C, and takes 50 Watts and 30 VARs. Is this system
balanced? Find the line currents at the source. Find the combined power absorbed by the
two loads.
8.
Assume a 480 V, balanced, 3 source feeds a balanced, Y-connected load with impedance
100 + j 100 Ω. Find the new power factor if a 2 F, -connected capacitor bank is added
to improve the power factor.
9.
Assume a 480 V, balanced, 3 source feeds a balanced, Y-connected load of 300 W with a
pf of 0.75 lagging. A new pf of 0.90 is desired. Find the required reactive power per phase
that must be added to achieve this new pf. Find the required capacitance if the capacitor
EECE 581 HW #2: pf Correction & 3 circuits
p. 2
bank is delta connected. Find the required capacitance if the capacitor bank is Y
connected.
10.
Assume a balanced, 120 V, 3 source feeds a delta connected load with impedance of 50 +
j 75 Ω. Draw the 3 diagram. Find the 3 power absorbed by the load using S = VI*.
Redraw the circuit twice, including 2 wattmeters in each circuit. Connect the meters in two
different ways to correctly measure the 3 active power using the 2-Wattmeter Method.
Give the meter readings for each case.