Understanding transformer failures
A basic winding schematic and an exploded construction drawing introduce the primary, secondary, magnetic core, bobbin and terminals. Electrical measurements then identify the winding or isolation path associated with a failure. Case photographs and microsections show how conductor fusion, insulation damage, fatigue and fretting relate to the measured symptoms.
What the paper covers
- Locating opens and unwanted winding-to-winding or winding-to-shield connections.
- Recognizing overcurrent fusion and dielectric breakdown.
- Comparing conductor spacing, insulation thickness and winding construction.
- Identifying lead fatigue, fretting wear, plating defects and contaminated interfaces.
- Tracing converter symptoms to board leakage and surrounding-circuit faults.
Analytical methods
Electrical continuity and resistance measurements, inductance comparisons, optical microscopy, radiography, dissection, microsectioning, SEM and EDS.
Author and technical reviewer: Ed Hare, PhD, SEM Lab, Inc. Published and reviewed 4 November 2026.