Use of dielectric-absorption tests in drying out large generators

DIELECTRIC absorption is the name commonly given to the effect which takes place in electrical insulation when it is subjected to a direct potential, with reference particularly to the manner in which the resulting charging current into the insulation decreases with time. The time rate of change and the magnitude of the observed current are indications of the amount of absorbed moisture (among other things) existing in the insulation of large generators, which apparatus affords a practical application of the dielectric absorption phenomenon. A newly wound generator or a generator long idle contains moisture in the insulation which should be removed before full operating voltage is applied to the winding insulation.¹ The method of using the dielectric absorption effect to determine the state of dryness of large generators is presented as a new means of measurement and one better adapted to giving more information than methods previously used.