What Happens During Transformer Commissioning?

Published 27 Aug 2026Updated 27 Aug 20267 min readIntermediateField Service
Quick answer — Transformer commissioning verifies the unit is fit and safe to energise: pre-commissioning checks (installation, tightness, oil level/quality, insulation tests and DGA), ratio and vector-group confirmation, protection and trip checks, auxiliary/cooling tests, then a controlled energisation (magnetisation inrush) and a period of observation and measurement before handover.
Contents
What is involved in commissioning a transformer?

Before energisation

Confirm the installation is complete and clean, all connections tight, the oil level and quality (BDV, moisture, DGA baseline) are good, the tank and conservator are correct, and the protection, tap-changer and cooling are set and tested.

Pre-commissioning tests

Runs insulation resistance and power-factor, turns ratio and vector group, winding resistance, and checks the OLTC operation and the protection relays and trip circuits.

Energisation

The unit is energised, normally under observation for magnetisation inrush, with no-load measurements and a check that the tap-changer, cooling and monitoring work.

Handover

After a stabilisation and observation period with DGA and temperature trending, the unit is handed over with the commissioning test report, settings and documentation.

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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