ELEN 3441 – Fundamentals of Power Engineering Lab # 15 Spring 2008 Lab 15: Transmission line.
Objective: to evaluate power loss along the transmission line depending on its length; to
observe voltage delivered to various types of load (resistive, inductive, and capacitive) by an
inductive transmission line and study the effects of load impedance compensation.
Equipment: Power Supply, DAI, Three-phase transmission line module (8329), Variable
resistance (8311), Variable inductance (8321), Variable capacitance module (8331).
Theory:
For the purpose of this exercise, a transmission line will be modeled by an inductive circuit,
whose reactance can be adjusted (Figure 15-1). The higher reactance, the longer is assumed the
transmission line represented by the module. The switch on the transmission line module turns
ON (upper position) and OFF (down position) the transmission line.
Figure 15-1
Experiment:
1) Construct the circuit shown in Figure 15-2. Hint: it may be more convenient to connect in
parallel resistive, inductive, and capacitive modules as a load.
Page | 1 ELEN 3441 – Fundamentals of Power Engineering Lab # 15 Spring 2008 Figure 15-2
Make sure the switch on the transmission line module is open (down position). Start the
Metering window and turn ON the following AC meters: E1, I1, E2, I2, real power
between E1 and I1, real power between E2 and I2. Also set two programming meters to
measure the apparent and reactive powers between E1 and I1 (at the generator’s end of
the line). Start the Phasor analyzer and set it to measure E1 and E2. Turn ON the PS.
2) Purely Resistive load: set the load resistance to 300 Ω (while keeping all capacitive and
inductive load switches OFF). Set the line reactance to 0 Ω (a very short transmission line
is modeled) and turn ON (upper position) the switch on the transmission line module.
Measure and record in a Data table the values of two voltages, two currents, and four
powers. Print the phasor analyzer’s screen to a pdf-file. Repeat the same measurements
(while recording the data in a Data table and printing the phasor analyzer’s screens to
pdf-files) for three other line reactances: 60 Ω, 120 Ω, and 180 Ω. Turn OFF the
transmission line switch.
3) Purely Inductive load: set the inductive load reactance to 300 Ω (while keeping all
capacitive and resistive load switches OFF). Set the line reactance to 0 Ω (a very short
transmission line is modeled) and turn ON (upper position) the switch on the
transmission line module. Measure and record in a Data table the values of two voltages,
two currents, and four powers. Repeat the same measurements, while recording the data
in a Data table, for three other line reactances: 60 Ω, 120 Ω, and 180 Ω. Set the Phasor
analyzer to measure E2 and I2. Print the phasor analyzer’s screen to a pdf-file for any one
value of load reactance. Turn OFF the transmission line switch.
4) Purely Capacitive load: set the capacitive load reactance to 300 Ω (while keeping all
inductive and resistive load switches OFF). Set the line reactance to 0 Ω and turn ON
(upper position) the switch on the transmission line module. Measure and record in a
Data table the values of two voltages, two currents, and four powers. Repeat the same
measurements, while recording the data in a Data table, for three other line reactances: 60
Ω, 120 Ω, and 180 Ω. Keep the Phasor analyzer to measure E2 and I2. Print the phasor
analyzer’s screen to a pdf-file for any one value of load reactance. Turn OFF the
transmission line switch.
Page | 2 ELEN 3441 – Fundamentals of Power Engineering Lab # 15 Spring 2008 5) Capacitive-Inductive load: set the capacitive load reactance to 300 Ω and the inductive
load reactance to 300 Ω parallel to each other (while keeping all resistive load switches
OFF). Set the line reactance to 0 Ω and turn ON (upper position) the switch on the
transmission line module. Measure and record in a Data table the values of two voltages,
two currents, and four powers. Repeat the same measurements, while recording the data
in a Data table, for three other line reactances: 60 Ω, 120 Ω, and 180 Ω. Keep the Phasor
analyzer to measure E2 and I2. Print the phasor analyzer’s screen to a pdf-file for any one
value of load reactance. Turn OFF the transmission line switch. Turn OFF the PS and
disassemble your circuit.
In your report:
1) Import the data you have collected in Parts 2, 3, 4, and 5 to Matlab. On four separate
figures, plot the following graphs: voltage across the load, apparent power at the
generator, reactive power at the generator, and the line losses for the four types of the
load (resistive, inductive, capacitive, and inductive-capacitive). For your graphs, use the
line reactance as arguments. Clearly label each plot. You must have four figures and four
graphs in each figure.
2) Considering the voltage across the load, what can you say about capacitive loads? Why
are they dangerous? Based on your observations (and graphs you present), what would
you suggest to mitigate the effects of capacitive loads?
3) Considering the reactive power at the generator, what would you conclude the main
difference between capacitive and inductive loads?
4) Compare the power losses between different types of loads. What do you conclude?
5) Report and compare four Phasor analyzer screenshots you have recorded in Part 2.
Describe and explain your observations.
6) Report and compare the three Phasor analyzer screenshots you recorded in Parts 3, 4, and
5. Describe them in terms of “current leading/lagging the voltage”. Are your observations
consistent with what was discussed in class? What do you conclude about the voltage and
current phase angles of the inductance and capacitance connected in parallel?
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