Objective: The purpose of this lab is to use power factor
correction (via a capacitor) to change a load's behavior such that it
appears purely resistive, i.e., had a power factor of 1.
Pre-lab:
For the circuit shown in Figure 1 below, determine the following:
impedance Z_{L} of the load
power factor angle of the load
power factor of the load
complex power absorbed by the load
expected time shift between the load's voltage and
current
Determine the value of a capacitor C that when placed in
parallel with the original load impedance (see Figure 2) yields an
equivalent power factor of 1. What is the value of this equivalent
impedance? What relationship do we expect between the compensated
load's voltage and current.
Laboratory Procedure:
Recall that average power absorbed by a device or circuit is P =
(1/2)VIcos(θ) W where V, I are the amplitudes of voltage and
current, respectively, and θ = φ_{V} -
φ_{I} is the phase difference between the element's
sinusoidal voltage v(t) and current i(t). To obtain the most efficient
use of the current delivered to a device or circuit, it is desired
that the load voltage and current be in phase (θ = 0 and pf =
1).
Investigate inductive load
An inductor is a coil of wire and wire has resistance. Measure
the resistance of your 0.47mH inductor. If this resistance is
significant include it your calculations.
Construct the following circuit.
Experimentally determine the load's impedance Z_{L},
power factor angle θ, power factor pf, and complex power
using voltage and current measurements. Compare these to your
predicted values found in the prelab.
Load power factor correction
Add a capacitor of the value determined in the prelab in
parallel with the original load as shown in Figure 2. Note the
value of the capacitor may need to be updated based upon the
resistance of the inductor.
Verify that your power factor correction is working. How do
the compensated load's voltage, current and impedance compare
to that predicted?
Normally, it isn't a good idea to change a circuit with input
and power applied, but carefully insert and remove the
capacitor while watching the load's voltage and current to
easily see the effect of the compensation.
Does your load compensation work at other frequencies other
than 10kHz? Investigate this both mathematically and
experimentally. Is there a difference in the load's behavior
as frequency is increased versus decreased?