# Vector Group of Transformer

Hi friends, in this article, I am going to describe the significance of vector group of transformer. It is very essential information for parallel operation of transformers and is very interesting as well.

Connection of transformer windings can be made in a number of ways. Accordingly, different types of connections have been standardized depending upon the phase displacement.

There are four vector groups and each group includes three methods of connection of high voltage and low voltage windings.

Phase displacement between EMFs of high voltage and low voltage windings is expressed as the clock hour number and is designated by symbols 0, 6, 1, and 11.

For example, the clock hour number 0 represents zero degrees phase displacement between primary and secondary EMFs. The clock hour number 6 is for 1800 phase displacement,  1 for  – 300, 11 for +300.

# Why vector group is important in transformer.

On the nameplate of three-phase transformer vector group is printed as Yy0, Dd1 etc. Here Yy0 will mean it’s both the windings are star-connected and phase displacement between primary and secondary EMFs is zero degree. It is belonging to Group No.1 (refer to table).

Similarly, Dy1 will mean its primary winding is connected in delta, secondary winding in the star, phase displacement is – 300 and belonging to Group No. 3.

Information of vector group of a transformer is very significant when it has to operate in parallel.  For a transformer working in isolation, the arrangement of its internal connections is of little importance.

Transformers will operate in parallel satisfactory if they have,

• the same primary and secondary voltages
• the same tap ratio
• the same percentage impedance, and,
• belonging to the same vector groups.

The two transformers may have their windings connected in star/star and yet it will not be possible to operate in parallel if one belongs to Group 1 and the other to group 2, unless the internal connections of the secondary winding of one of the transformers are changed.