THE CITADEL
THE MILITARY COLLEGE OF SOUTH CAROLINA
Department of Electrical & Computer Engineering
ELEC 204 Electrical Laboratory
EXPERIMENT 8
THREE PHASE POWER DISTRIBUTION
I) Pre-lab Assignment
No pre-lab.
II) Laboratory experiments
This laboratory provides the opportunity to investigate the characteristics of threephase power distribution and to verify the equations governing it using modules in the LabVolt unit mounted in the rack next to your lab bench. This unit is capable of generating
lethal voltages; thus, some safety precautions are essential.
• All connections will be made with the power turned off.
• When changing the wiring, the unit will first be turned off, the changes made, and
then the unit can be turned back on.
• Two jumper wires may not be spliced to form a longer one.
For this laboratory, the Fluke 8010 multimeters will be used to measure ac voltage
and current because they measure true rms values. There are two at each station.
The three-phase power source will be taken from the power-supply module in the
lower left corner of the Lab-Volt unit. Voltage source terminal definitions are as follows:
Schematic
Designator
a
b
c
n
Lab-Volt Unit
Terminal
4
5
6
N
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EXPERIMENT 8
THREE PHASE POWER DISTRIBUTION
Circuit A
A
a
45 0º
N
600
45 -120º
n
C
+
-
+
-
º
45 120
600
+
-
600
B
c
b
1) Measure and record the values of the three load resistors used, computing %deviation
from nominal.
2) Turn the voltage adjust knob fully counterclockwise on the power-supply module in
the lower left corner of the Lab-Volt unit.
3) With the power off, connect circuit A with one Fluke multimeter connected in series
with the A portion of the load to measure the current Ia-A. The other multimeter is to
be connected between nodes A and N to measure the voltage across the A section of
the load.
4) Turn on the power and slowly turn the voltage adjust knob on the power source until
45 V is measured across the load with the multimeter.
5) Measure and record the current in the A section of the load.
6) Turn off the power, and move the connections of the Fluke multimeters so that one
is set to measure the current in the B section of the load and the other is set to
measure the voltage across that section.
7) Turn on the power and adjust the voltage on the power source until 45 V is measured
across the load with the multimeter.
8) Measure and record the current in the B section of the load.
9) Turn off the power, and move the connections of the Fluke multimeters so that one
is set to measure the current in the C section of the load and the other is set to
measure the voltage across that section.
10) Turn on the power and adjust the voltage on the power source until 45 V is measured
across the load with the multimeter.
11) Measure and record the current in the C section of the load.
12) Turn off the power, and move the Fluke multimeter used to measure the current so
that it can measure the current in the neutral lead (In-N). Leave the voltmeter
connected across the C section of the load.
13) Turn on the power and adjust the voltage on the power source until 45 V is measured
across the C section of the load with the multimeter.
14) Measure and record the neutral current.
15) Turn off the power, and change the multimeter in the neutral path so that it
measures voltage. The high input impedance of the voltmeter eliminates the path for
current flow between neutral points and allows a measurement of the balance of the
load.
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EXPERIMENT 8
THREE PHASE POWER DISTRIBUTION
16) Turn on the power and adjust the voltage on the power source until 45 V is measured
across the C section of the loads with the multimeter.
17) With the other multimeter, measure and record the voltage difference between the
neutral points (Vn-N).
18) Turn off the power and turn the voltage adjust knob fully counterclockwise.
Circuit B
A
a
45 0º
1200
45 -120º
n
C
+
-
+
-
º
45 120
600
+
-
N
600
B
c
b
1) Measure the value of the 1200-Ω resistor and compute %deviation from nominal.
2) Perform steps 2) through 18) listed in circuit A above in order to measure the load
voltages and currents as well as the neutral current (In-N) and voltage differential
(Vn-N) between neutral points.
3) With the power off, remove the multimeter connection between the neutral points.
The remaining steps will be done with no connection between n and N.
4) Connect one multimeter so that it will measure the current in the A section of the load
and the other to measure the voltage of voltage source Van.
5) Turn on the power and adjust the source for a voltage reading of 45 V.
6) Measure and record the load current through section A.
7) Compute the load voltage for section A by multiplying the current measured in step
6) by the measured value of the resistance of that section.
8) Turn off the power, and move the multimeter connections to prepare to measure the
current through the B section of the load and the voltage across source Vbn.
9) Turn on the power and adjust the source for a voltage reading of 45 V.
10) Measure and record the load current through section B.
11) Compute the load voltage for section B by multiplying the current measured in step
10) by the measured value of the resistance of that section.
12) Turn off the power, and move the multimeter connections to prepare to measure the
current through the C section of the load and the voltage across source Vcn.
13) Turn on the power and adjust the source for a voltage reading of 45 V.
14) Measure and record the load current through section C.
15) Compute the load voltage for section C by multiplying the current measured in step
14) by the measured value of the resistance of that section.
16) Turn off the power and turn the voltage adjust knob fully counterclockwise.
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EXPERIMENT 8
THREE PHASE POWER DISTRIBUTION
Circuit C
a
A
45 0 º
600
+
1200
+
-
+
-
45 120
600
45 -120º
º
B
C
c
b
1) With the power off, connect circuit C with a Fluke multimeter set up to measure the
current Ia-A. Connect the other multimeter to prepare to measure the source voltage
Van. Use the same resistors that were used to build circuit B so that their measured
values are already known.
2) Turn on the power and adjust the source for a multimeter voltage reading of 45 V.
3) Measure and record the current Ia-A.
4) Turn off the power without touching the voltage adjustment knob. Change the
connection of the multimeter to measure the voltage across the AB section of the load
(VAB). Also, reconnect the other multimeter to measure the current Ib-B.
5) Turn on the power and measure VAB and Ib-B. Compute the load current IAB by
dividing VAB by the measured load resistance.
6) Turn off the power without touching the voltage adjustment knob. Change the
connection of the multimeter to measure the voltage across the BC section of the load
(VBC). Also, reconnect the other multimeter to measure the current Ic-C.
7) Turn on the power and measure VBC and Ic-C. Compute the load current IBC.
8) Turn off the power without touching the voltage adjustment knob. Change the
connection of the multimeter to measure the voltage across the CA section of the load
(VCA).
9) Turn on the power and measure VCA. Compute the load current ICA.
10) Turn off the power and turn the voltage adjust knob fully counterclockwise.
B
B
III) Lab Report
The lab report should be in standard format and include the following items:
1) Purpose of lab,
2) Model numbers of all test equipment used including the Lab-Volt modules,
3) Block diagrams of test setups,
4) Circuit schematics for A, B, and C with component values shown,
5) Nominal versus measured resistor values with %deviation,
Note: For every measured voltage and current that is put into the report, a
corresponding theoretical value computed by analyzing the circuit must also be
given. Use the measured values of the resistances in the computations.
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EXPERIMENT 8
THREE PHASE POWER DISTRIBUTION
Circuit A
6)
7)
8)
9)
Measured load voltage and current for each section,
Power dissipated in each section of the load and the total load power,
Current in the neutral wire (In-N),
Voltage difference between the neutral nodes with the neutral wire disconnected
(Vn-N from step 17),
Circuit B
10) Measured load voltage and current for each section with the neutral wire in place,
11) Power dissipated in each section of the load and the total load power,
12) Measured current in the neutral wire (In-N),
13) Voltage difference between the neutral nodes with the neutral wire disconnected
(Vn-N from step 17),
14) Load voltage and current for each section with the neutral wire disconnected,
15) Power dissipated by section and total power with the neutral wire disconnected,
Circuit C
16) Measured line currents Ia-A, Ib-B, and Ic-C ,
17) Measured load voltages VAB, VBC, VCA ,
18) Load currents computed from the measured load voltages,
19) Power dissipated by section and total load power, and
20) Conclusions.
B
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