What Is Clearance vs Creepage in a Transformer?
Quick answer — Clearance is the shortest distance through the air between two conductive parts; creepage is the shortest distance along the surface of an insulator between them. Clearance handles the air dielectric; creepage handles the contaminated or wet surface path. A higher pollution or voltage class needs a longer clearance and creepage, so the design sets both to avoid a flashover or a flash-over along the surface.
What is the difference between clearance and creepage?
Clearance
The air gap between conductors (or to earth). It must be large enough for the voltage and impulse, accounting for the air dielectric strength.
Creepage
The surface path along an insulator (bushing, barrier). It must be long enough so a contaminated or wet surface does not flashover; it is specified in mm/kV by the pollution class.
Why both
Both are needed: clearance for the air gap and creepage for the surface, and both are set by the voltage and the site (altitude and pollution).
References & standards
- IEC 60076-3
- IEC 60815
Related
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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