Humidity Absorption of Generator Bars

The absorption of humidity in electric insulation systems is dominant for the behaviour of the insulation resistance and the breakdown strength. For this reason the dryness of the insulation system is tested as a routine test, e.g. the humidity of insulating oil at transformers. The dryness of generators is evaluated by measuring the time constant of the electric insulation. In an Austrian recommendation for the condition evaluation of rotating machines the humidity and insulation condition is evaluated by an empirical established dryness boarder. Since this evaluation method was recognized new insulation materials and production technologies for generator bars developed. This paper should give a view to the behaviour of the physical knowledge base of humidity absorption of solid insulation systems. The surface and volume resistance in dependence to temperature and air humidity for different insulation systems for rotating machines is measured and discussed