What Is a Continuously Transposed Conductor (CTC)?

Published 27 Aug 2026Updated 27 Aug 20266 min readIntermediateManufacturing
Quick answer — A continuously transposed conductor is a bundle of several rectangular enamel-covered strands (typically 3 to 100s) that are continuously transposed — each strand continuously swaps position — so every strand experiences the same leakage field and the same average impedance. This dramatically reduces eddy (circulating) losses and keeps current sharing even in large windings.
Contents
What is a CTC (continuously transposed) transformer conductor?

Why transposition matters

In a large transformer winding, strands at different radial positions see different leakage flux, which drives circulating currents between strands and high stray (eddy) losses. Transposing the strands so each occupies every radial position equally cancels the net induced EMF difference and evens the current.

Construction

Strands are individually enameled for interstrand insulation, wrapped with one or two layers of paper, and arranged and transposed at regular intervals. Strand counts and sizes are chosen to match the winding current and to control the strand-level eddy loss.

When it is used

CTC is standard for large power-transformer and reactor windings where current is high and stray loss would otherwise dominate. It is often specified in offshore and generator-step-up transformers where losses and hotspots carry a heavy penalty.

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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