PD phenomena on dielectric surfaces under DC stresses influenced by air humidity

Based on fundamental investigations of the charge accumulation on the surface of dielectric materials relevant for DC test equipment, it was found that partial discharge (PD) phenomena under DC stresses are affected by both local and remote charge generation. With increasing air humidity both charge generation processes are intensified, resulting in an unexpectedly strong reduction of the PD inception voltage. It is therefore concluded that DC test equipment for operating voltages ≳100 kV working in atmospheric air cannot be designed fully PD free at reasonable cost