how to do tan delta test of transformer?

To perform a tan delta test on a transformer, first ensure the transformer is de-energized and properly grounded. Connect the test equipment, typically a power factor test set, to the transformer’s bushings. Apply a voltage, usually at the rated frequency, and measure the capacitance and power factor (tan delta) of the insulation system. The tan delta value indicates insulation quality; higher values suggest deterioration. Analyze the results against industry standards for assessment.