Principle of water-cooled insulation resistance meter

This is an instrument specially used to measure the stator insulation resistance of water-cooled generators. Its structure and principle are much more complicated than ordinary meggers. Since the stator coil of the internal dual water cooling unit has several plastic royal tubes connected with the cooling water, the measurement error of ordinary megger is very large. This type of special megger needs to use 220V AC power supply when measuring. There is a balanced deck inside. Adjusting the bridge balance can eliminate the impact of the water cooling circuit on the insulation. Since I haven't been in contact with him for a long time, I only have this small impression.