WAZIPOINT Engineering Science & Technology: Three-phase Transformers FAQs

Saturday, January 7, 2023

Three-phase Transformers FAQs

Working principle of three-phase transformer
Fig: Three-phase transformer working principle, photo collected from TAMESON site.

What is a three-phase transformer?

A three-phase transformer comprises three sets of primary and secondary windings, each wound around one leg of an iron core assembly.

Working principle of three-phase transformer

Electrical Transformer Working PrincipleThe primary winding of the three-phase transformer is energized from a three-phase supply. Then, the flux is produced in the core by the primary currents in the three windings.

Advantages of three-phase transformer 

The main advantages of the three-phase transformer over than single-phase transformer is as below:

  • It is lighter and smaller. 
  • It requires less space to install. 
  • Low cost compared with three units of single-phase transformers. 
  • Transportation is easy and also transportation cost is less.
Three-phase power supplies are more efficient. A three-phase power supply can transmit three times as much power as a single-phase power supply, while only needing one additional wire (that is, three wires instead of two).

3-types 3-phase transformer

Small power transformers, 

Medium Power transformers, and 

Large power transformers.

What is RYB in a transformer?

RYB simply stands for Red, yellow, and Blue respectively in a three-phase electrical system. In a three-phase electrical system, the three phases are separated by an angle of 120 degrees, and each phase is given a specific color.

The most common 3-phase transformer connections

The delta–wye connection is the most commonly used three-phase transformer connection. The wye-connected secondary allows a single-phase load to be distributed among the three phases to neutral instead of being placed all on one winding as with a four-wire delta secondary.

A combination of three-phase transformers is used

These four standard configurations are given: 

  • Delta-Delta (Dd), 
  • Star-Star (Yy), 
  • Star-Delta (Yd), and 
  • Delta-Star (Dy).

Three single-phase transformers may be connected together between their primary and secondary three-phase circuits.

Can it use more than a 3-phase transformer?

Yes, but not used normally, because the cost of the electrical system increases. The three-phase system delivers three times the power of a single phase. The 6 phase adds twice the power of the 3 phase. The drawback of more phases is that the transmission towers have to sustain more loads of conductors.

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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