ANGULAR DISPLACEMENT OF THREE PHASE TRANSFORMERS BASIC AND TUTORIALS

Angular displacement is defined as the phase angle in degrees between the line-to-neutral voltage of the reference-identified high-voltage terminal and the line-to-neutral voltage of the corresponding identified low-voltage terminal.

The angle is positive when the low-voltage terminal lags the high-voltage terminal. The convention for the direction of rotation of the voltage phasors is taken as counterclockwise.

Since the bulk of the electric power generated and transmitted is three-phase, the grouping of transformers for three-phase transformations is of the greatest interest. Connection of three-phase transformers or three single phase transformers in a three-phase bank can create angular displacement between the primary and secondary terminals.

The standard angular displacement for two-winding transformers is shown in Figure above. The references for the angular displacement are shown as dashed lines.

The angular displacement is the angle between the lines drawn from the neutral to H1 and from the neutral to X1 in a clockwise direction from H1 to X1.

The angular displacement between the primary and secondary terminals can be changed from 0 to 330 degrees in 30deg steps simply by altering the three-phase connections of the transformer.

Therefore, selecting the appropriate three-phase transformer connections will permit connection of systems with different angular displacements.

Figure shows angular displacement for common double-wound three-phase transformers. Multicircuit and autotransformers are similarly connected.