Grounded Wye-Delta Transformer Bank Backfeed Short-Circuit Currents

A common load on a distribution feeder consists of a combination single-phase lighting load and a three-phase load such as an induction motor. This combination load can be served by a wye-delta transformer bank. The question is whether the wye connection should be directly connected to ground, connected to ground through a grounding resistor or left ungrounded. During normal loading conditions, each connection has advantages and disadvantages. However, during a short-circuit condition, a grounded wye-delta bank will provide a "backfeed" short-circuit current for an upstream ground fault. This paper will develop methods for the analysis of the backfeed currents for an upstream line-to-ground fault.