how to carry out insulation resistance test on a transformer?

To carry out an insulation resistance test on a transformer, first ensure the transformer is de-energized and isolated from the power supply. Connect an insulation resistance tester (megohmmeter) to the transformer’s windings and ground. Typically, test each winding to ground and between windings. Apply the test voltage (usually 500V or 1000V) for a specified duration, often 1 minute. Record the resistance values; a reading above 1 M? is generally acceptable, indicating good insulation.