Influence of humidity on pulse shape parameters of positive corona discharges in air at DC voltage

The partial discharge diagnosis is a valuable method for the condition assessment of operating equipment. The phase resolved pattern as an established diagnostic tool under AC voltage stress enables to draw conclusions regarding the location and the type of fault. The inapplicability to DC voltage stress coupled with the increasing importance of DC transmission systems requires the development and evaluation of alternative and suitable basic approaches. Several diverse promising approaches are identified, whereby recent investigations are, up to now, limited to standard atmospheric conditions. To reach universally valid statements, additional research regarding the influence of varying conditions is required. Focusing on the pulse shape of positive corona discharges in air a measurement method for investigating the influence of the humidity is presented. Pulse shape parameters are determined, compared to each other and reconciled with physical processes for two temperatures and five different relative humidity levels in the range of 22 % to 95 %.