ECEN 2612
AC Power Measurements (10.0 points)
Lab #2
Name:
Partner:
Purpose: To observe and measure real and reactive power in AC circuits; to use a wattmeter (WM),
which contains both a voltmeter (VM, placed IN PARALLEL with the load) and an ammeter
(AM, placed IN SERIES with the load) to make these power measurements.
Procedure:
The instructor will explain the Variac power source, the load impedances, and the instrumentation to be used in this
experiment. Listen carefully and take some notes. Caution is very important in this lab: there are relatively dangerous
voltages and currents available. Notice that the Variac source is capable of “ampere-level” currents. Be sure to use the
correct loads which are also able to handle the currents. YOU WILL NOT BE USING LOAD ELEMENTS STORED IN
THE BACK CABINETS. USE ONLY THE EQUIPMENT THAT THE INSTRUCTOR HAS SPECIFIED. Also, the
resistors used in this lab are rheostats WHICH BECOME HOT when operating. Be VERY careful!!!
1. Set up the circuit shown by starting with load (1) and connecting to the AM and VM on only
PHASE 1 (PH1) of the wattmeter. Check your setup with the instructor BEFORE turning anything
on! Turn on the wattmeter and use the default settings at startup. (The wattmeter auto-ranges
measurements by default, so you don’t need to adjust the ranges.) Press the “PH1” button on the
wattmeter to display simultaneous V, A, W, and VAR measurements for Phase 1.
2. Always start with the Variac off and dialed down to zero. Using load (1) for the load, slowly
increase the Variac voltage from 0 V until the load voltage reads 100 Vrms on the VM. Watch
the ammeter as you increase the voltage, and be sure to stop if you see any sudden increase in the
load current when you increase the voltage. That would indicate a wiring problem.
Circuit:
Loads:
3. Record the load voltage Vrms with VM on the WM, the load current Irms with AM on the WM, and
the real load power P and reactive power Q with the wattmeter. (1.0 point)
4. Repeat steps 1 & 2 for loads (2), (3), and (4). Remember to turn off the Variac when making a
change, and start the Variac voltage at zero and increase it slowly for each new load. (2.0 points)
5. Now turn the Variac off and disconnect the load. Using the LCR meter set at a 100 Hz signal,
measure and record parameter values (R, L, and C) for each of the four elements used in the loads.
Be sure to include the resistance in the inductor and the inductance in the resistors. Then
calculate the resistance and reactance of each load at f = 60 Hz using the formulas. (1.0 points)
6. Write a description of each load. Discuss why we do not use decade resistance boxes for R!
What is special about the L and C loads that we use for this lab?
J.Hosseininejad / P.Munro 12-Feb-2016 08:56 PM
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7. Using your data and the given AC power formulas, calculate the following experimental values
for each load: a) apparent power |S|, b) impedance magnitude |Z|, c) impedance angle Z ,
d) equivalent resistance R, e) equivalent reactance X, and f) power factor pf. Tabulate data and
results, showing all measured and calculated quantities for each load. Include the step 4 results for
R and X in the table. Your table should have 12 rows and 4 columns as shown below: (4.0 points)
LOADS
QUANTITY
(units)
#1 (R)
#2 (RL)
#3 (RC)
#4 (C)
Vrms (V rms)
Irms (A rms)
P (W)
Q (VAR)
|S| (VA)
Z (Ω)

R (step 7) (Ω)
X (step 7) (Ω)
pf
R (step 5) (Ω)
X (step 5) (Ω)
AC POWER FORMULAS
S  Vrms I rms ; Q   S 2  P 2 [+ inductive;  capacitive]
Z
P
Vrms
; Z  cos1
S
I rms
[+ inductive;  capacitive]
For Step 5: R = sum of load resistance measurements from LCR meter
XR = ωL
XL = ωL
XC = -1/(ωC) where ω = 2πf
For Step 7: R 
pf 
P
S
P
I
2
rms
; X
Q
2
I rms
[leading if capacitive; lagging if inductive]
REPORT: Keep a complete record of all data, results, observations, and answers to questions. Write neatly, legibly, and
clearly on the unlined side of standard engineering paper. (2.0 points)
Attach this lab sheet as a cover. This is due at the beginning of the next lab session.
J.Hosseininejad / P.Munro 12-Feb-2016 08:56 PM
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