These are the test doing after repair of power transformers to know reliability
¢ insulation resistance (core and structure-core);
¢ polarity, phase angle displacement and phase sequence;
¢ voltage ratio;
¢ winding ohmic resistance;
¢ windings and core insulation resistance measurements (Megger test);
¢ windings insulation power factor and capacitances;
¢ condensing bushings capacitances and power factors;
¢ no-load losses and excitation current at 90%, 100% and 110% of rated voltage (AC separate
source);
¢ load losses with reduced current (separate AC source); and
¢
short-circuit impedances.
In some cases, special on-site tests are also performed, namely:
¢ frequency response (FRA);
¢ infrared-scan; and
¢ acoustic emission and partial discharge location; and
¢ insulation characterization through RVM or dielectric spectrography.
i cant see any reports of repair of power transformers
but its similar topics and check it please ...