Download Active, Reactive and Apparent Power

EET 152 Laboratory 9
Active, Reactive and Apparent Power
Power Factor Correction
Calculations
Part 1: RC Circuit
1. For the RC circuit shown below, calculate the voltage across the resistor, capacitor
and the source voltage. Record these values in Table 1(magnitude only).
2. Using the current and voltage for each element, calculate the power associated with
each element. Record these powers in Table 1. Include in the table the type of power
for each element, such as active, reactive, or apparent.
3. Determine the power factor for this RC circuit.
Power factor = _____________
4. Draw the power triangle for this circuit.
Part 2: RL Circuit
5. For the RC circuit shown below, calculate the circuit current and the voltage across
the resistor and the inductor. Record these values in Table 1 (magnitude only).
6. Using the current and voltage for each element, calculate the power associated with
each element. Record these powers in Table 1. Include in the table the type of power
for each element, such as active, reactive, or apparent.
7. Determine the power factor for this RL circuit.
Power factor = _____________
8. Draw the power triangle for this circuit.
Circuit
RC
Circuit
RL
Circuit
Component
Resistor
Capacitor
Source
Resistor
Inductor
Source
Table 1
Rms Magnitude
Current
Voltage
Magnitude
Power
Units
Type
2.0 mA
Part 3: Power Factor Correction
9. For the circuit shown below, find the current drawn from the source with the switch
open. Note that the open switch removes the capacitor, which creates a circuit that is
the same as Part 2 RL circuit.
I total = _____________
10. Using the circuit current and Ohm’s Law, calculate the voltage across each element
and the powers for each element when the switch is open. Record these values in
Table 2. Again, recognize the values will be the same as Part 2.
11. A capacitor must be chosen so that when the switch is closed, the reactive power of
the inductor will be cancelled by the reactive power of the capacitor. Calculate the
value of capacitor necessary and verify this value with your instructor.
12. With the switch closed, the net Q should be zero. Record the reactive power of the
capacitor. Record the apparent power in Table 2 as the same value found for the
active power of the resistor.
13. Use the source voltage and apparent power to calculate the value of the source current
when the switch is closed. Record this value in Table 2 and verify its accuracy with
your instructor.
14. Draw the power triangle for the circuit when the capacitor has been added.
Switch
Position
Component
Switch
Open
Resistor
Power
Current
Voltage
Magnitude
Units
Type
0
0
0
0
0
Inductor
Capacitor
Source
Switch
Closed
Table 2
Magnitude
1.0
Resistor
Inductor
Capacitor
1.0
Source
1.0
Laboratory Work
Part 1: RC Circuit
1. Assemble the circuit shown. Set the source to a frequency of 5 kHz and raise the
amplitude of the generator until the current in the circuit is 2.0 mA.
2. Use the digital multimeter to measure and record the voltages across the resistor and
capacitor. Record these values in Table 3.
3. Use the values in Table 3 to calculate the power for each component. Record these
values, including units in Table 3.
4. Calculate the power factor for this circuit.
Power factor = _______________
Table 3
Component
Rms magnitude
Voltage
Current
Magnitude
Power
Unit
type
470 
.1 uF
Source
2.0 mA
Part 2: RL Circuit
5. Assemble the circuit shown below. Leave out the capacitor. Verify the source
frequency is 5.0 k Hz and adjust the output to 1.0 Volt.
6. Use the digital multimeter to measure the voltages across the resistor and the
inductor. Record these in Table 4. Also measure the circiut current and record in
Table 4.
7. Use the values in Table 4 to calculate the power for each component. Record these
values, including units in Table 4.
8. Calculate the power factor for this circuit.
Power factor = _______________
Part 3: Power Factor Correction
9. Use the capacitor decade boxes and the RLC bridge meter to obtain a capacitor value
of approximately .0147 uF. Connect the required capacitor decade boxe(s) into the
circuit (in parallel with the resistor and inductor).
10. Verify that the source remains at 5 kHz and 1.0 volt.
11. Use the digital multimeter to measure the voltage across the capacitor, resistor and
inductor. Also, measure the source current and the current through each branch of the
circuit. Record these values in Table 4. Recognize that the voltages and currents for
the inductor branch should remain unchanged from Part 2.
12. Using the measurements, calculate the power for each component, including units.
Record in Table 4.
13. Calculate the power factor for this circuit.
Power factor = _______________
14. As a check, compare your power factor to that found in step 8. The power factor with
the capacitor in the circuit should be much closer to 1. If it is not, an error has been
made.
Table 4
Circuit
Capacitor
not in the
circuit
Component
Power
Current
Voltage
Magnitude
Units
Type
0
0
0
0
0
Resistor
Inductor
Capacitor
Source
Capacitor
in the
circuit
Magnitude
1.0
Resistor
Inductor
Capacitor
1.0
Source
1.0
Active, Reactive and Apparent Power
Power Factor Correction
Questions
Part 1: RC Circuit
1. Using the data in Table 3 and Ohm’s Law, calculate the actual resistance of your
resistor and the capacitance of your capacitor. Are these values within tolerance?
(Hint: use R=VR/I and Xc=VC/I)
2. Using percent error calculations, compare the apparent power measured in the
laboratory section (Part 1 step 2) with the apparent power calculated in the calculation
section (Part 1 step 3).
Part 2: RL Circuit
3. Using the data in Table 4 and Ohm’s Law, determine the inductance of your inductor.
(Hint: use XL=VL/I)
4. How does RCOIL effect the calculations performed in question 3?
5. Using percent error calculations, compare the apparent power measured in the
laboratory section with the apparent power calculated in the calculation section.
Part 3: Power Factor Correction
6. Why did the current from the source drop when the capacitor was added to the RL
circuit?
7. Why did apparent power delivered by the load drop although the real power disipated
by the resistor remain the same?