## EE 212 Lab

### Lab 15: Phase Shifters and Three-Phase Power

The purpose of this lab is to design and build a variable phase
shifter and use it to simulate a three-phase power system.

**Before coming to lab** design a circuit using op--amps and
a constant amplitude phase shifter to simulate a 3-phase generator.
There should be one input for a sine wave. Choose a frequency greater
than 1 kHz for your model. There should be three low impedance outputs
$120^\circ$ apart. Each output should have $V_{RMS}$ of 1.2~V.
The ground or common of
the input can serve as the common or neutral of the outputs
(Figure~1). You should be able to design the circuit using three
op--amps, two capacitors, two pots, and several resistors.
- Have your instructor check your design before building it. You should
have a neat schematic with pin numbers. Carefully construct the
circuit, and check wiring carefully before turning on power.
- Connect a 1~k$\Omega$ load to all outputs. Make adjustments
to the produce the proper phases and amplitudes. Measure and record the
line-to-line and line-to-neutral voltages using a voltmeter. Compare
these to the expected ones.
- Connect your 3-phase generator to a balanced Y-load, each of
a 1~k$\Omega$ resistor. Use 100$\Omega$ in each line to simulate a
long line. Measure the voltage from n to N, and adjust the phases to
make this voltage as close to zero as possible. Measure the current
in each line and in the neutral.
- Unbalance the load by replacing one of the 1~k$\Omega$
resistors with a 2~k$\Omega$. Remeasure the currents. In particular,
note the change in current in the neutral.