ECET 3500 Lab 3
Transformer Characteristics
MEASUREMENTS
1. Open Circuit Test
I. Connect the following circuit, using winding 1–2 as the primary winding.
I oc
1
5
4
+
+
Poc
-
 Open-circuited secondary
winding 5-9
E oc
-
N
2
9
II. Apply rated voltage, EOC, to the primary winding.
III. Measure IOC and POC, the current and real power supplied to the primary winding. Record all three
“open-circuit” parameters; EOC, IOC, and POC.
EOC = __________V IOC = __________A POC = __________W
IV. Lower the supply voltage to zero and turn OFF the supply, but do not disassemble the circuit.
2. Short Circuit Test
Important Note – The short circuit test is typically performed by supplying rated current to the
primary winding of the transformer while the secondary winding is short-circuited. Due to the
short-circuit conditions, this test only requires a small primary voltage.
**** Applying too large of a primary voltage may damage the transformer. ****
I. With the circuit still connected as required for the “open circuit test”, place a “short” (jumper wire)
across the secondary winding (5–9) of the transformer as shown in the following figure:
Isc
1
5
4
+
+
Psc
N
 Short-circuited secondary
winding 5-9
Esc
2
9
II. Check to be sure that the supply voltage is set to zero, and then turn ON the supply.
III. Carefully increase the voltage until rated current, ISC, is applied to the primary winding.
III. Measure ESC and PSC, the voltage and real power supplied to the primary winding. Record all three
“short-circuit” parameters; ESC, ISC, and PSC.
ESC = __________V ISC = __________A PSC = __________W
IV. Lower the supply voltage to zero and then turn OFF the supply.
V. Remove the “short” (jumper wire) connected across the secondary winding.
ECET 3500 Lab 3
Transformer Characteristics
3. Load Tests
I. Connect a load resistance of 15 to the secondary winding (winding 5-9).
II. Adjust the voltage of the source connected to winding 1-2 such that it supplies rated voltage to that
winding.
III. Measure and record the values of the primary current, the secondary voltage, and the secondary
current.
VPRI = 120V IPRI = ________A VSEC = ________V ISEC = ________ A
IV. Replace the load resistor with an inductor that has a reactance of 15 and repeat the measurements.
VPRI = 120V IPRI = ________A VSEC = ________V ISEC = ________ A
V. Replace the inductor with a capacitor that has a reactance of 15 and repeat the measurements.
VPRI = 120V IPRI = ________A VSEC = ________V ISEC = ________ A
VI. Lower the supply voltage to zero and then turn OFF the supply.
VII. Have your instructor check your values, and then disassemble the entire circuit.
4. Transformer Ratings
I. Record the ratings of the windings upon which the OC and the SC tests were performed.
________VARATED ________VRATED(1-2) ________A RATED(1-2) ________V RATED(5-9) ________A RATED(5-9)
REPORT GUIDELINES
Your instructor may provide additional requirements as to the format and/or content of your report.
In general, your report should be well-written in a neat and logical manner. All of your measured
data must be shown in your report, and a sample calculation that shows both the formula and the
numerical values utilized to achieve the final result must be provided for each unique calculation.
For this experiment, you must write a report that presents all of the measurements performed during
the experimental portion of the lab. Additionally, you must also complete the following tasks and
include all of the required work along with the results in your report:
1. Open Circuit (OC) Test (Measurements – Part 2)
Use the results from the Open Circuit Test to determine the values of the core loss parameters, Rfe and
Xm within the practical transformer model, with both referenced to the primary-winding (1–2).
2. Short Circuit (SC) Test (Measurements – Part 3)
Use the results from the Short Circuit Test, to determine the values of the winding loss parameters, Req
and Xeq within the practical transformer model, with both referenced to the primary-winding (1–2).
3. Practical Transformer Model Parameters and Drawing
Create a table that presents the values of all four of the impedance parameters for the practical
transformer model as determined from the Open Circuit and Short Circuit tests.
Provide an accurate drawing of the practical transformer model that shows all of the model’s
components labeled with both their parameter names and their numerical values. Additionally,
label all of the voltages and currents within the transformer model.
4. Load Calculations
Using the practical transformer model that you developed in the previous step, calculate the expected
primary current, secondary voltage, and secondary current of a 15 resistor is connected across
the secondary winding and the primary winding is supplied at rated voltage.
Repeat the load calculations, but this time for a purely inductive load reactance of 15 connected
across the secondary winding.
Once again, repeat the load calculations, but this time for a purely capacitive load reactance of 15
connected across the secondary winding.
Tabulate the complete set of load calculations.
Compare the calculated results for the three loads to those measured during the Load Test portion of
the lab.
5. Conclusion
Discuss the overall results of the laboratory experiment as they relate to the theoretical operation of a
practical transformer.
Also, discuss whether or not the load test/calculation results correspond with the results of Voltage
Regulation tests that were performed during the last three steps of Lab 02.