Wye-Delta or Star-Delta Connection Transformers

Why Transmission Line Transformers are used as  Star-Delta or Star-Wye connections? 

The main use of the star-delta or star-wye connection is at the substation end of the transmission line where the voltage is to be stepped down. 

The primary winding is wye (Y)-connected with grounded neutral as shown in the above figure-Connection Diagram of the Wye-Delta or Star-Delta Connection Transformers. 

The ratio between the secondary and primary line voltage is 1/ 3 times the transformation ratio of each trans-former. 

There is a 30° shift between the primary and secondary line voltages which means that a Y − ∆ transformer bank cannot be paralleled with either a Y − Y or a ∆ − ∆ bank. Also, third harmonic currents flow in  ∆ to provide a sinusoidal flux.

What Is The Difference Between A Star And A Delta Connection?

Star Connection	Delta Connection
1.     Line current = phase current	1.Line current = √3 × phase current
2.     Line voltage = √3 phase voltage	2.     Line Voltage = Phase Voltage
3.     Total power = √3 × VL × IL ×power factor	3.     Total power = √3 × VL × IL × power factor
4.     Phase voltage is √3 times less than the line voltage due to which the number of turns it takes to winding is less. This saves copper.	4.     Due to the same line voltage and phase voltage, the number of turns in the winding of this connection is high.
5.     Neutral is available in it.	5.     Which is not neutral.
6.     Due to the availability of neutral, 2 types of voltages are available such as 240 Volt phase voltage and 415 Volt line voltage. Hence the lighting load on a single phase and power load on 3 Phases can be added to this connection.	6.  Only 415 volt 3 Phase is available in this connection. For this reason, you cannot take a load of 1 single phase in it.
7.     In this the line voltage is 30° leading to this phase voltage.	7.     In this line current it is 30° leading from phase current.
8.     It has a lower breakdown voltage.	8. It has a low breakdown voltage.

Difference Between Star-Delta Connection and Star-Delta Starter

Hi guys, you may be confused hearing the star-delta connection!!

You may be read another topic with a star-delta connection like below:

Star-Delta Connection Using for Motor Starting

Star delta starters are another device that may be used to reduce current demand during motor startup. It is often used for starting three-phase induction motors, but can only be used when starting the motor without load and when the required starting current is relatively low...

So, it was a star-delta starter, which means a motor starter device.

But, this article is limited to a three-phase transformer connection for the power transmission network.

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.