how to megger a three phase transformer?

To megger a three-phase transformer, first ensure the transformer is de-energized and disconnected from the power source. Connect the megohmmeter leads to the primary and secondary windings, testing each phase individually. Measure the insulation resistance between each winding and ground, as well as between windings. Record the readings, ensuring they meet the manufacturer’s specifications. A minimum insulation resistance of 1 M? per kV of operating voltage is typically recommended.