ELEC 226, Spring 2011
Prof. Rich Kozick

Laboratory 4: More Transformers

Objective: We will do more measurements with the transformers from Lab 3. We will use the equations for the linear transformer in Figure 13-8 and Section 13-2.2, and also the ideal transformer in Section 13-4. Notes are provided that summarize the formulas for linear and ideal transformers.

Please keep your circuits assembled until you discuss the results with the instructor, and bring your results to class on March 10.

Lab Activities:

  1. Please study the analysis of the linear transformer and make sure you understand equations (13.23)-(13.25) and the notes.

  2. We will use the outer terminals on the transformer box as the primary and the AC cord terminals as the secondary, so the turns ratio is expected to be approximately n = N2 / N1 = 10 (as defined in equations 13.35 and 13.36 in Chapter 13 of the text).

  3. Use a frequency of 200 Hz and characterize your transformer at this frequency. That is, estimate the internal resistances of the primary and secondary coils (R1 and R2) and the self-inductances (L1 and L2). You should be able to estimate R1, R2, L1, and L2 quickly using your experience from Lab 3.

    Before you make your measurements for R1, R2, L1, and L2, devise a procedure to estimate the mutual inductance, M, and the coefficient of coupling, k (defined via ). Make additional measurements to allow you to estimate M and k.
    (Hint: Can you estimate M with an open-circuit at the secondary?)

  4. Next add a load resistor RL across the secondary terminals, so current will flow in both the primary and the secondary. Measure the phasors V1, V2,  I1, and I2. Compare the measured results with the linear transformer equations as well as the ideal transformer equations:  
                 




    Determine how closely your transformer measured results match with the linear and ideal transformer equations.

 

Each lab group should prepare a summary of your analysis and measured results and discuss it with the instructor before leaving. Then each student is asked to explain all analysis and measurements for submission by the end of the day on Friday, March 11 to Judy Harris in the Electrical Engineering Department office in Dana 301.

 

In the work that you submit, you should include for each case (1) a diagram of the circuit that you constructed, showing the component values and the voltages and currents; (2) your measured values of voltage and/or current; and (3) the computations that you performed. Your work will be evaluated based on the correctness of the approach rather than the accuracy of the results.