The vector group of a transformer is a notation used to represent the phase relationship between the primary and secondary windings. It provides information about the arrangement of the windings and the electrical characteristics of the transformer concerning phase shifts and connections. The vector group is crucial for understanding how transformers behave in terms of voltage and current relationships.

The vector group notation consists of a combination of letters and numbers, each conveying specific information:

**Letters:**The letters in the vector group represent the phase displacement between the primary and secondary windings. The most common letters used are ‘Y’ (star) and ‘D’ (delta), indicating whether the windings are connected in a star or delta configuration. For example, ‘Y’ signifies a star connection, while ‘D’ indicates a delta connection.**Numbers:**The numbers in the vector group denote the phase shift between the primary and secondary windings. The most common numbers used are 0, 11, 1, and 10. These numbers represent the angular displacement in degrees between the primary and secondary voltages. For example, a transformer with a vector group of ‘Yd1’ means the primary winding is in star (Y) configuration, the secondary winding is in delta (d) configuration, and there is a 30-degree phase shift (1) between the primary and secondary voltages.

Common vector group notations include:

**YNyn0 or Dyn11:**The primary winding is in star (Y), the secondary winding is in star (y), and there is a 180-degree phase shift (0) between the primary and secondary voltages.**YNd11:**The primary winding is in star (Y), the secondary winding is in delta (d), and there is a 30-degree phase shift (11) between the primary and secondary voltages.**YNd1:**The primary winding is in star (Y), the secondary winding is in delta (d), and there is a 30-degree phase shift (1) between the primary and secondary voltages.

Understanding the vector group is essential for various reasons, including the proper parallel operation of transformers, synchronization in power systems, and the design of transformer protection schemes. It ensures that transformers in a power system are correctly connected and that their phase relationships align for efficient and safe operation.