Oil immersed power transformers are widely applied in transmission and distribution systems due to their robust insulation structure and excellent heat dissipation capability. In such critical applications, wiring group selection goes far beyond simple electrical connection and becomes a key technical parameter influencing system compatibility, power quality, and operational reliability.
In oil immersed transformers, the phase displacement of ±30° is internally determined by the winding configuration method, the relative arrangement of high-voltage and low-voltage windings, and the internal lead routing and terminal connection sequence.
Once the transformer leaves the factory, this phase displacement cannot be altered through external reconnection.
For example, the widely used Dyn11 wiring group achieves a 30° voltage lag of the low-voltage side relative to the high-voltage side through specific internal winding connections.
Our engineers support EPC contractors and power utilities with wiring group selection based on system phase sequence, grounding method, and harmonic conditions.
Consult Our Transformer EngineersThe delta (D) winding provides a closed circulation path for third harmonic currents, preventing them from entering the power system. This is particularly important for oil immersed transformers, as it reduces additional core and winding losses, prevents localized overheating, and extends insulation service life.
Effective harmonic suppression directly supports long-term thermal stability.
Oil immersed transformers with YN (star with neutral brought out) connections allow direct integration into effective grounding systems.
When combined with delta windings (such as YNd11), they enable controlled zero-sequence current flow, flexible grounding strategies, and compliance with different grid fault protection requirements.
Oil immersed transformers with different wiring groups (for example, Yd1 and Yd11) must never be operated in parallel.
Phase displacement differences will cause circulating currents, leading to overload tripping, excessive thermal stress, and internal mechanical damage.
Proper wiring group selection, such as Dyn11, helps to suppress harmonic distortion, reduce total system losses, improve voltage waveform stability, and protect downstream sensitive equipment.
This contributes directly to higher energy efficiency and stable system operation.
New power distribution projects:
Dyn11 is generally the preferred choice for harmonic suppression and grounding safety.
Industrial expansion or grid connection:
New transformers must match the existing system wiring group and phase sequence.
Renewable energy power stations (e.g., PV booster stations):
Wiring group and grounding method must comply strictly with grid code requirements.
The wiring group of an oil immersed transformer is the cornerstone of its electromagnetic design. A mismatch between transformer vector group and system configuration may result in parallel operation failure, protection misoperation, or degraded power quality.
The cost of post-installation correction is far higher than careful selection during the initial design stage.
We provide customized winding connections and wiring group designs based on your system phase sequence, harmonic environment, and grounding requirements.
Technical exchanges based on specific project parameters are welcome.
We provide customized oil immersed transformer designs for EPC projects, substations, and utility power systems.
