EGR 325
HW 3
due Sept 24
4pm, room 352
Using the PowerWorld Simulator, do the following three problems.
1. Open Problem 2_32 (in chapter 2 of the GSSampleCases folder, in the Simulator
folder). This system has an 8 MW/4 MVAr load that is supplied at 13.8 kV
through a feeder with an impedance of 1 + j2Ω. The load is compensated with a
capacitor whose output, Qcap, can be varied in 0.5 MVAr steps between 0 and 10.0
MVArs.
a. What value of Qcap minimizes the real power line losses?
i. Include a screen shot of the PowerWorld one-line diagram for this
value of Qcap. State/show how you determine the real power line losses.
b. What value of Qcap minimizes the MVA power flow into the feeder?
i. Include a screen shot of the PowerWorld one-line diagram for this
value of Qcap. State/show how you determine the MVA power flow into
the feeder. State what “MVA power flow into the feeder” actually is.
c. Why would a power company be interested in the results of (a) and/or (b)
above? (very brief comment)
d. Why would a consumer be interested in the results of (a) and/or (b) above?
(very brief comment)
e. Plot the real and reactive line losses as Qcap is varied between 0 and 10.0
MVArs. Briefly comment on the meaning and/or significance of these
losses and interpret your plot.
2. Load PowerWorld Simulator case Problem 6_46. Plot the reactive power output
of the generator at Bus 2 as a function of its voltage set point value in 0.005 pu
voltage steps over the range between its lower limit of -50MVAr and its upper
limit of +50MVAr.
a. What is the significance of the reactive power output of a generator, to the
owner of the generator? … to the power system? (very brief comments)
(Note: To change the generator 2 voltage set point first select Tools, Play to
begin the power flow simulation and then click on the up/down arrows on
the bus 2 magenta voltage set point field.)
3. Open Problem 6_59. This models a seven bus system. Bus 7 is the slack bus. The
real power generation/load is shown at each bus, while the per unit reactance of
each of the lines (on a 100MVA base) is shown in yellow. Your task is an openended one. Find one (or two related) things to change on this system that lead to
unexpected, or non-intuitive results.
a. State what you did, perhaps with an annotated figure of the one-line
diagram to aid your explanation.
b. State why the results are unexpected or non-intuitive.
c. Pose one or two explanations of what is happening in the system as you
make these changes and as the system responds to your changes.
d. Be brief! We are early in the semester. I do not expect you to “know”
what is going on in a power flow case. The objective here is to start
playing and start gaining some intuition.