Type, Routine and Special Tests? What Is the Difference?

Published 27 Aug 2026Updated 27 Aug 20265 min readBeginnerTesting
Quick answer — Routine tests are run on every unit (ratio, resistance, no-load and load loss, power factor, HV/LV withstand, oil test). Type tests are run on a design once to prove it (temperature rise, impulse, short-circuit withstand). Special tests are run by agreement (sound level, zero-sequence, harmonics, DGA).
Contents
What is the difference between type, routine and special transformer tests?

Routine tests

Performed on each manufactured unit to confirm it meets the specification and is free of defects: turns ratio, winding resistance, no-load and load loss, insulation power factor/resistance, applied-voltage and induced-voltage tests, and oil tests.

Type tests

Proven once on a representative design and then applied to all units of that design: temperature-rise, lightning-impulse, switching-impulse and short-circuit withstand tests.

Special tests

Run only by agreement with the customer for particular requirements: sound level, zero-sequence impedance, harmonic and stray-loss tests, dissolved-gas or frequency-response analysis.

References & standards

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Book seriesAcademy

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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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