How do you choose vector group is voltag step up transformer?

A vector group table lists the 'phase shift' or 'angular displacement' for all combinations of three-phase transformer connections. In order to parallel three-phase Transformers, their angular displacements (amongst other things) must be the same.

'Phase shift' or 'angular displacement', is defined as 'the angle by which the secondary line-to-line voltage lags the primary line-to-line voltage'.

Angular displacement depends on the type of transformer connection. The most common are:

• delta/delta results in an angular displacement of 0o or 180o
• wye/wye results in an angular displacement of 0o or 180o
• delta/wye results in an angular displacement of 30o or 210o
• wye/delta results in an angular displacement of 0o or 180o

In a Vector Group table, though, the angular displacement is normally expressed in multiples of 30o -e.g. '11', which means 11x 30o, or 330o.

From the above data, it would be impossible to parallel, for example, a delta/delta transformer with a delta/wye transformer.

BS 171 lists twelve main connections, arranged in four main groups according to their angular displacements. A connected designated, for example, 41 Dy 11, shows:

• 4 -the fourth main group
• 1 -the first connection within that group
• D -HV connection is connected in delta
• y -indicates LV connection is in wye
• 11 -indicates an angular displacement of (11x30o)= 330o.