What Is a Traction Transformer?

Published 27 Aug 2026Updated 27 Aug 20266 min readIntermediateApplications
Quick answer — A traction transformer supplies railway traction systems, either on-board the locomotive (an auxiliary and sometimes traction transformer) or in the trackside substation that steps the grid voltage down to the catenary voltage (e.g. 25 kV, 15 kV or 750 V DC). It must handle vibration, frequent load cycles, reduced space and fire-safe requirements, and be robust in a demanding environment.
Contents
What is a traction transformer and why is it different?

Trackside vs on-board

Trackside traction transformers convert the utility voltage to the catenary voltage at the substation; on-board transformers (on rail vehicles) supply the drives and auxiliary loads and are subject to severe vibration and space limits.

Design demands

They need a ruggedised construction for vibration, dust and temperature; often dry-type or ester-filled for fire safety; and they handle high, rapidly varying loads with frequent starts and stops.

Standards

Rail projects add specific traction and fire-safety requirements in addition to the IEC/utility rules and the local grid interface.

References & standards

Related

Book seriesAcademy

Related manufacturers

Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp

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Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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