What is the connection group of a transformer?

Transformer Connection Group

The connection group of a transformer refers to the phase difference between the primary and secondary voltages or currents. It is determined by the winding directions of the primary and secondary coils, the labeling of their start and end terminals, and the connection mode. Expressed in a clock-like format, there are 12 groups in total, numbered from 0 to 11.

The DC method is commonly used to measure the transformer's connection group, mainly to verify whether the connection group indicated on the nameplate matches the actual measurement result. This ensures that the conditions for parallel operation are met when two transformers are operated in parallel.

In essence, the transformer connection group is a way to represent the combined wiring form of the primary and secondary windings. There are two common winding connection methods for transformers: "delta connection" and "star connection". In the transformer connection group notation:

• "D" denotes a delta connection;
• "Yn" denotes a star connection with a neutral wire;
• "11" indicates that the line voltage on the secondary side lags behind the line voltage on the primary side by 30 degrees.

The representation method of the transformer connection group is as follows: uppercase letters represent the connection mode of the primary side, and lowercase letters represent the connection mode of the secondary side.