ELEC 226, Spring 2003

Prof. Rich Kozick

Prof. Rich Kozick

**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.

**Questions for you to answer:**

- 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 = N*_{2}/*N*_{1}> 1. - 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.

- 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. - Devise measurement procedures that will allow you to estimate the
internal resistances of the primary and secondary
(
*R*_{1}and*R*_{2}), the self-inductances (*L*_{1}and*L*_{2}), and the coefficient of coupling,*k*.Do your measurements agree with the "ideal transformer" assumptions?

- Attach a 10k ohm load resistor to the secondary, and measure
the impedance at the primary terminals,
*Z*_{ab}, at 60 Hz. Compare your measurement with analysis based on the ideal transformer model. - Set up the circuits shown in Problem 9.66 that you analyzed on Homework 2, and compare your measured results with the analysis.