how to do an insulation resistance test on a transformer?

To perform an insulation resistance test on a transformer, first ensure the transformer is de-energized and disconnected from the power supply. Use a megohmmeter to apply a test voltage, typically between 500V and 1000V, across the windings and between the windings and the ground. Record the resistance readings, which should ideally be above 1 M?. If the readings are low, it may indicate insulation deterioration. Always follow safety protocols during testing.