What Is a Unit (Station) Transformer?
Quick answer — A unit (or station) transformer supplies the auxiliary power to a power plant (pumps, fans, controls) and is fed either from the generator terminals (a unit transformer) or from the grid (a station/start-up transformer). A unit transformer steps the generator voltage down to the plant auxiliary voltage, so the plant can run and start up.
What is a unit / station transformer at a power plant?
Unit transformer
It is connected to the generator terminal and steps the voltage down to the plant auxiliary (e.g. 13.8 kV to 400 V / 6.6 kV) for the pumps, fans, drives and controls.
Station / start-up transformer
It is fed from the grid and provides a start-up (black-start) source so the plant can be started when the generator is off, and can supply the auxiliaries in an emergency.
Why it matters
Reliable auxiliary power is essential to run and start the plant, so the unit/station transformer is critical to availability and is usually well-protected and monitored.
References & standards
- IEC 60076-1
- IEEE C57.12.00
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
Related components
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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