Engr228
Lab #7
Power Factor Correction
Name ___________________________
Grade _______/10
Introduction
Voltage and current waveforms as applied to motors tell us a great deal about the power environment
surrounding the motor. This lab will guide you through the calculation of various power quantities as
applied to an induction motor. Calculations will be done to verify the advantages from improving
power factor.
Lab Objectives
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Apply classroom principles and theory to physical devices;
Understand complex power issues using a real motor;
Understand the benefits of power factor correction.
Equipment
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Induction motor;
Benchtop DMM’s;
Handheld DMM’s;
Wattmeter;
Capacitor decade box.
References
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Pre-lab #7 assignment;
Circuits text book;
Circuits laboratory instruments handout.
Procedure
The data for this last lab of the quarter will be gathered from one setup so everyone will use the same
data in their calculations. Note that the lab instructor will operate the motor and explain the procedure.
1. The induction motor is connected as shown in the figure above. Initially, there is no capacitor
in the circuit so IC = 0 amps. Once the motor has been started and has stabilized, measure the
line voltage (VL), the power (P), the line current (IL), and the motor current (IM). Record this
data in the table on the following page. Shorting wires will be installed by the lab instructor
around the ammeters before starting the motors to avoid damage caused by the large
starting current of the motor.
2. From the measurements in step 1, calculate the power factor of the load and the parallel
capacitance required to correct the power factor to unity. Enter those numbers in the same
table.
VL (V)
P (W)
IL (A)
IM (A)
Step 1
Step 2
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Step 3
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IC (A)
Ccalc (µF)
Cexp (µF)
pf
0.0
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3. Tell the lab instructor what value of capacitance you have calculated from step 2. After the lab
instructor has placed your calculated value of capacitance in the circuit, find the value of
experimental capacitance required to correct the power factor to unity and enter this value in
the table above. Also measure and record the voltage, power, and currents in the table above.
4. Calculate the percent reduction in line current by correcting the power factor to unity.
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 − 𝑛𝑒𝑤
%𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 = 𝑥 100%
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙
% reduction: __________
5. Assuming the line resistance of the wires feeding the motor (load) is 5Ω, calculate the percent
reduction in the voltage drop across the wires when the power factor is corrected to unity.
% reduction: __________
6. Assuming the line resistance of the wires feeding the motor (load) is 5Ω, calculate the percent
reduction in the power lost in the line when the power factor is corrected to unity.
% reduction: __________
7. State your observations and conclusions.