In most medium- and low-voltage distribution networks, you'll find transformers configured as Dyn11. This isn't by chance; Dyn11 offers the best combination of technical performance, operational stability, and system compatibility, making it the preferred choice for distribution applications.
Dyn11 offers an advantage over Dyn1 in applications involving non-linear loads. Still, a matching vector group is the main criterion when selecting between these two vector groups in view of the need for parallel operation and avoidance of circulating currents.
1. HV Winding – Delta (D)
The delta connection provides a closed path for third-harmonic components of magnetizing current, preventing their appearance in the supply system. It allows operation with unbalanced secondary loads while maintaining balanced HV line currents. It also helps limit voltage imbalance and transient transfer to the LV side - acting as a stabilizing "buffer" between network and load.
2. LV Winding – Star (y) with Neutral (n)
The star connection on the secondary provides a neutral point, enabling 3-phase, 4-wire distribution systems. It supports both single-phase and three-phase loads, simplifying earthing and fault protection, as fault currents return through the neutral.
3. Phase Displacement – "11" Clock Position (30° Lead)
In Dyn11, the LV line voltage leads the HV by 30°. This allows for parallel operation with other Dyn11 units without generating circulating currents and ensures compatibility with the standard R–Y–B phase sequence in distribution systems.
4. System Compatibility & Performance
Dyn11 suits standard 11/0.4 kV and 33/0.4 kV networks. It performs well under unbalanced and non-linear loads, and the closed delta traps 3rd harmonics - improving LV voltage waveform quality. The grounded neutral enhances protection coordination and overall network stability.