Single-Phase Transformers

Electromechanics Laboratory
Electrical Engineering 208
Experiment 3
Single-Phase Transformers
Cooperative Engineering Program
Springfield, MO
Laboratory Work
Begin by connecting the Lab Volt console to the single-phase power source. Then turn on the
console and connect it to the laboratory computer.
Lab Volt Single-Phase Transformers
The Lab Volt single-phase transformers are rated at 500 VA and the primary side voltage is 120
V AC (RMS). There are two secondary windings which are to be connected in series to make
the secondary voltage 120 V (RMS) also. The rated current in the primary side is 0.5 A.
Short Circuit Test
Short circuit the secondary terminals of transformer. Slowly increase the voltage applied to
primary side of the transformer until the primary current reads 0.5 A. At that point quickly
measure the voltage, current, and power. Allow the short circuit current to flow in the secondary
for only as long as it takes to make the measurements, the shut off the power.
Open Circuit Test
Apply rated voltage to the primary with the secondary open. Measure the voltage, current, and
power. Observe the current waveform on the oscilloscope and then adjust the oscilloscope so
that the voltage is displayed on the horizontal axis and the current is displayed in the vertical
axis. The resulting curve is the hysteresis loop for the iron core of this transformer. Print out the
hysteresis curve.
Load Test
Connect the transformer to a series RL load of equal R and XL values. Measure the voltage,
current, and power across the load. Repeat with an RC load.
Using the values of the transformer parameters obtained from the open- and short-circuit tests
develop a circuit model and use the circuit model compare the voltage, current, and power values
predicted by the model with those measured for the RL and RC loads.