THREE PHASE TRANSFORMER POLARITY EFFECTS AND STANDARD ANGULAR DISPLACEMENT BASICS AND TUTORIALS

THREE PHASE TRANSFORMER POLARITY EFFECTS AND STANDARD ANGULAR DISPLACEMENT BASIC INFORMATION
Polarity Effects And Standard Angular Displacement Of Three Phase Transformers


Polarity Effects
Any combination of additive and subtractive units can be connected in three-phase banks so long as the correct polarity relationship of terminals is observed.

Whether a transformer is additive or subtractive does not alter the designation of the terminals (X1, X2, etc.) thus correct polarity will be assured if connections are made as indicated in the diagrams.

The terminal designations, if not marked, can be obtained from the transformer nameplate which shows the schematic internal-connection diagrams diagramming the actual physical relationship between the high and low voltage terminals.

If subtractive-polarity transformers are used in threephase banks secondary connections are simplified from those shown for the additive-polarity units.

The additivepolarity connections, for standard angular  isplacement, are somewhat complicated, particularly in cases with delta-connected secondary, by the crossed secondary interconnections between units.

For this reason simplified bank connections, which give non-standard angular displacement between primary and secondary systems, are sometimes used with additive-polarity units.

Standard Angular Displacement
Standard angular displacement or vector relationships between the primary and secondary voltage systems, as defined by ANSI publications, are 0° for delta-delta or wye-wye connected banks and 30° for delta-wye or wye-delta banks.

Angular displacement becomes important when two or more three-phase banks are interconnected into the same secondary system or when three-phase banks are paralleled. In such cases it is necessary that all of the three-phase banks have the same displacement.

The following diagrams cover three-phase circuits using:

1. Standard connections—where all units have additive polarity and give standard angular displacement or vector relation between the primary and secondary voltage systems (as defined by ANSI publications).

2. Simplified connections for the more common three phase connections with the delta-connected secondary— where all units have additive polarity but give nonstandard angular displacement between the primary and secondary voltage system.