Combining a grounding transformer with an auxiliary winding is feasible only when both duties are defined simultaneously. Ground-fault current can impose short-time heating while the auxiliary winding carries continuous station load; the two thermal states may overlap. Specify grounding duty, auxiliary kVA and power factor, voltage regulation expectations, loading coincidence and protection independently so neither function is hidden inside the other.
Prepare a simultaneous-duty matrix
List at least the normal auxiliary load, maximum continuous neutral current, grounding fault with auxiliary load present, and recovery after the fault. Mark any assumed load shedding rather than silently relying on it. The winding starts a fault event from its existing thermal state, not necessarily from ambient temperature. A combined unit should therefore be evaluated against the specified overlap of duties, not merely against two independent ratings that were each calculated from a cold start.
Check auxiliary voltage during grounding duty
Auxiliary kVA alone does not describe the quality of the station supply. Request the expected voltage regulation for its load power factor and any permitted disturbance during a ground fault. If controls, cooling motors or protection auxiliaries depend on that winding, define their ride-through or alternate-supply arrangements at system level. Do not assume that the grounding function guarantees an uninterrupted or tightly regulated auxiliary output under every fault on the main bus.
Make the shared failure consequence explicit
Combining functions reduces the number of separate units but also creates a shared outage boundary. An internal fault or maintenance outage can remove both the grounding source and the auxiliary supply. The protection design must distinguish an auxiliary feeder fault from a fault requiring removal of the combined transformer, while preserving the required grounding state of the bus. Include that contingency in the station availability review before treating the combined arrangement as interchangeable with two independent devices.
Technical reference framework
[1] IEC 60076-8:1997 — Application guide.
[2] IEC 60076-1:2011 — Power transformers, General.
[3] Post Glover GT110-08 — Zig-zag grounding transformers.