Power supply method of power transformer

The 10kV high-voltage power grid operates using a three-phase, three-wire, ungrounded neutral system.

Most user transformers use a Yyn0 connection configuration with a directly grounded neutral system, enabling three-phase four-wire or five-wire power supply, such as the TN-S system.

Three-phase transformers and transformer banks can be connected in star, delta, or zigzag configurations, represented by Y, D, and Z symbols on the high-voltage side and y, d, and z symbols on the low-voltage side. When a neutral point is provided, high-voltage is represented by YN and ZN symbols, and low-voltage by yn and zn symbols. There are 12 possible connection groups depending on the different wiring combinations of the three-phase windings. However, for ease of manufacturing and use, my country originally specified five connection groups: Y, Yn0 (Y/Y0-12); Y, Yn (Y/Y-12); YN, Yn (Y0/Y-12); Y, d11 (Y/Δ-11); YN, d11 (Y0/Δ-11).