The wye connection – also known as a star connection – is one of the two fundamental connection types for three-phase systems. The three windings are joined together at a common neutral point. This connection is standard in many distribution and power transformers, as well as in numerous industrial motors. The star connection is one of the elementary configurations of three-phase technology and shapes the behavior of countless machines and transformers worldwide.
What advantages does the wye connection offer?
In a star system, the voltage across each individual winding is smaller by a factor of √3 than the voltage between two line conductors. This allows windings to be sized for a lower voltage stress. The neutral point can also be earthed, offering significant advantages for the protection concept and earth-fault protection.
Key Characteristics at a Glance
- Common neutral point of the three windings
- Winding voltage smaller by a factor of √3 than the line-to-line voltage
- Neutral point can be earthed – advantages for the protection concept
- Often used on the high-voltage side of transformers
- Can be combined with delta connections in vector groups such as Dyn5 or YNd11
- Line voltage is √3 times the phase voltage
- Neutral point treatment directly affects earth-fault behavior
Frequently Asked Questions
When is a star connection used instead of a delta connection?
A star connection is particularly suitable when neutral-point earthing is required – for example for protection concepts or to limit earth-fault currents. At high voltages, the lower winding voltage of the wye connection is also an advantage.
What does the designation “Yn” mean in a vector group?
The capital “Y” stands for a star connection of the corresponding winding. The appended letter “n” indicates that the neutral point is brought out (accessible). This results in designations such as Yyn0, Dyn5, or YNd11, which clearly describe the connection and phase shift.
How does neutral-point treatment affect the grid?
With solid earthing, high currents flow in the event of an earth fault, allowing selective disconnection. With an isolated or resonant-earthed (Petersen coil) neutral point, the grid remains operational for hours even during an earth fault, offering higher security of supply but requiring special protection concepts.
When is star-delta starting used for motors?
For three-phase motors from around 5 kW upward, star connection is initially used at startup to reduce the starting current. Once rated speed is reached, the connection is switched to delta. Today, variable frequency drives often take over this function – they enable both a smoother start and energy savings.
Do you need advice on the right vector group and protection concept for your transformer? Our engineering team is happy to support you – get in touch with us.