Insulation Levels for Turbogenerator Rotors

The advent of large generators, requiring higher excitation powers, has led to a steady increase in excitation voltage magnitude. This in turn has meant increases in the pressure test level which the rotor winding must withstand. At present there are differences in the specified pressure test levels in various countries. On the European Continent ent there is a maximum pressure test limit of 3,500 volts, irrespective of the excitation voltage, whilst on the North American Continent the pressure test voltage is 10 times the rated excitation voltage with no maximum limit.