How to Test a Transformer: Methods, Sequence and Interpretation
To test a transformer, begin with isolation, visual inspection and nameplate review, then select safe offline tests such as insulation resistance, turns ratio, winding resistance, excitation current and oil tests; interpret results against factory data, phase balance and historical trends. No single test proves health. Test voltage, temperature, connection, instrument accuracy and transformer type affect results. Medium- and high-voltage testing requires qualified personnel, approved procedures and controlled discharge and grounding.
