WAZIPOINT Engineering Science & Technology: Transformer Equivalent Circuit Diagram

Sunday, April 23, 2023

Transformer Equivalent Circuit Diagram

How to draw the Equivalent Circuit Diagram of a Transformer?

If you want to draw the Transformer equivalent circuit, it would be like the below:

Transformer Equivalent Circuit
Fig: Equivalent Circuit Diagram of a Transformer.

What should be considered during drawing the Transformer equivalent circuit diagram?

Considering the two major parts of a transformer- primary winding and secondary winding with their parameters the equivalent circuit would be as above;

R1 = Primary Winding Resistance.
R2= Secondary winding Resistance.
I0= No-load current.
Iµ = Magnetizing Component,
Iw = Working Component,
This Iµ & Iw are connected in parallel across the primary circuit. 

The value of E1 ( Primary e.m.f ) is obtained by subtracting vectorially I1Z1 from V1

The value of X0 = E1 / I0 and R0 = E1 /Iw

We know that the relation of E1 and E2 is E2 /E1 = N2 /N1 = K.  The K is known as the Transformation Ratio.

Calculation of Transformer Equivalent Circuit Diagram

Now, you can easily calculate the total impedance to transfer voltage, current, and impedance either to the primary or the secondary from the equivalent circuit of a transformer  considering the parameters below:

Transformer Equivalent Circuit Diagram

Why Transformers Are Rated In KVA instate of KW?

From the below transformer open circuit or no-load test and short circuit or Impedance test on Transformer, it can be seen that Cu (Copper) loss of a transformer depends on current, and iron loss depends on voltage. This means the total transformer loss depends on Voltage and Current (VA). It does not depend on the phase angle between voltage and current. We can say the transformer loss is independent of the load power factor. This is the reason that transformers are rated in kVA instates of KW.

You may know the details about the electrical transformer from the following articles:

  1. Working Principle of Transformer;
  2. Transformer Construction;
  3. Core-type Transformers;
  4. Shell-type Transformers;
  5. Elementary Theory of an Ideal Transformer;
  6. E.M.F. Equation of Transformer;
  7. Voltage Transformation Ratio;
  8. Transformer with losses but no Magnetic Leakage;
  9. Transformer on No-load;
  10. Transformer on Load;
  11. Transformer with Winding Resistance but no Magnetic Leakage;
  12. Equivalent Resistance;
  13. Magnetic Leakage;
  14. Transformer with Resistance and Leakage Reactance;
  15. Simplified Diagram;
  16. Total Approximate Voltage Drop in Transformer;
  17. Exact Voltage Drop;
  18. Equivalent Circuit Transformer Tests;
  19. Open-circuit or No-load Test;
  20. Separation of Core Losses;
  21. Short-Circuit or Impedance Test;
  22. Why Transformer Rating in KVA?;
  23. Regulation of a Transformer;
  24. Percentage Resistance, Reactance, and Impedance;
  25. Kapp Regulation Diagram;
  26. Sumpner or Back-to-back-Test;
  27. The efficiency of a Transformer;
  28. Condition for Maximum Efficiency;
  29. Variation of Efficiency with Power Factor;
  30. All-day Efficiency;
  31. Auto-transformer;
  32. Conversion of 2-Winding Transformer into Auto-transformer;
  33. Parallel Operation of Single-phase Transformers;
  34. Questions and Answers on Transformers;
  35. Three-phase Transformers;
  36. Three-phase Transformer Connections;
  37. Star/Star or Y/Y Connection;
  38. Delta-Delta or ∆/∆ Connection;
  39. Wye/Delta or Y/ Connection;
  40. Delta/Wye or ∆/Y Connection;
  41. Open-Delta or V-V Connection;
  42. Power Supplied by V-V Bank;
  43. Scott Connection or T-T Connection;
  44. Three-phase to Two-Phase Conversion and vice-versa;
  45. Parallel Operation of 3-phase Transformers;
  46. Instrument Transformers;
  47. Current Transformers;
  48. Potential or Voltage Transformers.

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