Question

With the Aid of a sketch of delta and star connection diagram, state the basic equation from which the delta star, star delta conversion equation can be derived.

The above diagram indicates that transformation ratio is not merely the transformer turn ratio, but involves the type of connection.

Thus for a delta star arrangement

Transformation ratio = V1 / V2 = Vph1/ √3Vph2 = N1 / √3N2

Irrespective of whether the delta star or star delta connection is used, no trouble is experienced with third harmonic current, since they circulate round the mesh.

A star point is available if a 4 wire arrangement is required for earthing purpose.

For marine works star delta working allows an acceptable arrangement since a star point on the alternator is usual and a neutral can be introduced at a later stage, should this be considered advantageous