How Is a Transformer Failure Investigated?

Published 27 Aug 2026Updated 27 Aug 20268 min readAdvancedField Service
Quick answer — A failure investigation combines records and evidence: the protection and alarm history, DGA trend and gas composition, oil quality, insulation test results, visual and bore-scope inspection of the windings and core, and any external damage or event. The goal is to identify the root cause (electrical, thermal, mechanical or environmental) and its origin so the replacement or repair and any design/life changes are correct.
Contents
How is a transformer failure investigated?

Gather the data

Collect the protection events, currents and voltages, the DGA trend and gas ratios, oil tests (BDV, moisture, acidity), temperature records, and any site history such as overloads, lightning or pollution.

Inspect and test

Perform insulation resistance and power-factor, turns ratio, winding resistance, and a visual or bore-scope inspection of the windings, core, tap-changer and leads. Look for deformation, track marks, burns and displaced conductors.

Correlate and diagnose

Match the electrical evidence (e.g. acetylene for arcing) to the physical findings (e.g. a shorted turn) and to the likely event, so the root cause and the responsible sub-component are identified.

Recommend

State the cause, recommend the repair or replacement and the corrective actions (e.g. protection settings, cooling, oil treatment), and any design changes for future units.

References & standards

Related

Book seriesAcademy

Related manufacturers

Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp

Related components

Protection, monitoring & diagnostics Oil, fluids & preservation Conductors & core steel
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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