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.

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.