how to perform tan delta test on transformer?

To perform a tan delta test on a transformer, first, ensure the transformer is de-energized and properly grounded. Connect the test equipment to the transformer’s bushings. Apply an AC voltage, typically at the rated frequency, and gradually increase it to the test voltage level. Measure the capacitance and the power factor (tan delta) of the insulation system. Analyze the results to assess insulation condition; a high tan delta indicates potential insulation degradation.