The delta-grounded transformer

MANY DISTRIBUTION SYSTEMS are fed essentially from one high-voltage system through transformation. It is sometimes desirable to ground both systems at the substation which is the main source of supply to the distribution system. This grounding problem may be solved by using either a Y-Y-delta transformer with a tertiary delta winding or a conventional Y-delta bank with a separate grounding transformer. However the tertiary delta winding in the first case and the zigzag windings of the grounding transformer in the second, both remain idle under normal load conditions. In addition, a separate grounding transformer is a source of permanent no-load losses, and it requires space and extra equipment in the switchyard. The higher initial and operating costs inherent in these schemes are reduced by the use of a delta-grounded power transformer, first suggested by H. L. Hoeppner.¹