ELEC 226, Spring 2003
Prof. Rich Kozick

## Laboratory 2: Transformers

Objective: We will learn more about transformers by setting up and performing measurements with transformer circuits. We will test some of the transformer circuits discussed in lectures and homework problems.

1. Use a 1 volt sinusoidal voltage source at 60 Hz to determine the primary and secondary sides of your transformer. Define the secondary as the side with the larger number of turns, and make measurements to estimate the turns ratio, a = N2 / N1 > 1.

2. Apply a 6 volt DC voltage source to the primary, and place a neon bulb across the secondary. Disconnect the source at the primary, and the bulb will flash.
Be careful - you can get shocked at the secondary!!
• In your lab notebook, explain what is happening in this circuit.
• Make measurements at the secondary to determine the "dots" on the transformer. For safety, you should reduce the DC voltage for these measurements.

3. Repeat step 1 at frequencies other than 60 Hz, and check whether the turns ratio, a, varies with frequency. You may want to make a plot of a versus frequency. Check a frequency range that spans several decades.

4. Devise measurement procedures that will allow you to estimate the internal resistances of the primary and secondary (R1 and R2), the self-inductances (L1 and L2), and the coefficient of coupling, k.

Do your measurements agree with the "ideal transformer" assumptions?

5. Attach a 10k ohm load resistor to the secondary, and measure the impedance at the primary terminals, Zab, at 60 Hz. Compare your measurement with analysis based on the ideal transformer model.

6. Set up the circuits shown in Problem 9.66 that you analyzed on Homework 2, and compare your measured results with the analysis.