Three-phase Transformer Connections

Three-Phase Transformer Connection Procedure in Electrical Energy Transmission

The three-phase transformer consists of three transformers either separate or combined with one core. The primary and secondary of the transformer can be independently connected either in the star or delta. There are four possible connections for a 3-phase transformer bank.

Single-phase three transformers or three single cores in a three-phase transformer are mainly connected in Delta or Star way to form a three-phase transformer.

The most common uses of three-phase transformer connection are as below:

1. Delta – Delta: Δ – Δ (Delta – Delta) Connection;
   
2. Star – Delta: Υ – Υ (Star – Star) Connection;
   
3. Delta – Star: Δ – Υ (Delta – Star) Connection;
   
4. Star – Delta:Υ – Δ (Star – Delta ) Connection.

Also, there are some special connection arrangements for three-phase transformer connections, like-

1. Open-Delta or V-V Connection;
2. Power Supplied by V-V Bank;
3. Scott Connection or T-T Connection.

Three-phase Transformer Line Voltage and Current

The relationship between the three-phase transformer connection in primary and secondary, line voltage in primary and secondary windings, and line current in the primary and secondary end is as below:

Primary-Secondary Configuration	Line Voltage Primary or Secondary	Line Current Primary or Secondary
Delta – Delta
Delta – Star
Star – Delta
Star – Star

If you want to learn more about transformers, you may go to the transformer index.

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.