Delta-Wye Connection of Transformers

 

Delta-Star or Delta-Way Connection of Transformers

Delta-star or Delta-Way connected transformers are mainly used in power distribution or near before consumer end. 

Delta-Star transformer uses the Delta connection of its primary coils where the balanced load is supplied from the utility company. 

On the other hand, secondary coils are connected as a star or Y form where there is a chance of an unbalanced load. 

The secondary windings provide the required 4th-wire neutral or earth connection for using a single-phase or three-phase load.

Three-phase Voltage and Current

Connection	Phase Voltage	Line Voltage	Phase Current	Line Current
Star	VP = VL ÷ √3	VL = √3 × VP	IP = IL	IL = IP
Delta	VP = VL	VL = VP	IP = IL ÷ √3	IL = √3 × IP

In the star connection line current and phase current are the same; similarly, in the delta connection, the line voltage is equal to the phase voltage.

In the star connection phase voltage is equal to the line voltage divided by root three; similarly, in the delta connection, the phase current is equal to the line current divided by root three.

Delta-Star Turns Ratio

Where, 

TR= Turn Ratio

N_p= Primary turn

N_s= Secondary turn

V_p= Primary Voltage

V_s= Secondary voltage

The ratio is the relationship between the number of primary winding turns to the number of secondary winding turns—and thus a comparison between the primary phase voltage and the secondary phase voltage. For typical delta/delta systems, the ratio is 2:1—but for typical delta/wye systems, the ratio is 4:1.

Advantages of Delta-Star Connected Transformer

-On the primary side due to the delta connection and winding cross-section required is less.

-On the secondary side, neutral is available, which can be used for a 3-phase, 4-wire supply system.

-No distortion due to third harmonic components.

-Large unbalanced loads can be handled without any difficulty.

-Assuming that the neutral of the Y-connected secondary circuit is grounded, a load-connected phase-to-neutral or a phase-to-ground fault produces two equal and opposite currents in two phases in the primary circuit without any neutral ground current in the primary circuit.

The disadvantage of the Delta-Star Transformer

In the Delta-Star Transformer connection, the secondary voltage is not in phase with the primary voltage. 

So,  it is not possible to operate the Delta-Star Transformer connection in parallel with the star-star or the delta-delta-connected transformer.

To know all about transformers the article Transformer working principle and uses in the electrical engineering field will help you.

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.