how to megger test a 3 phase transformer?

To perform a megger test on a 3-phase transformer, first ensure the transformer is de-energized and isolated. Disconnect all secondary connections and connect the megger leads to the primary and secondary windings. Test each phase individually by applying the megger voltage (typically 500V or 1000V) for a specified duration, usually 1 minute. Record the insulation resistance readings, which should be above the manufacturer’s minimum requirements. Finally, compare the readings across phases for consistency.