Experiment investigation of partial discharges under impulse voltage

Partial discharge is defined by IEEE as an electrical discharge that only partially bridges the insulation between conductors and that may or may not occur adjacent to a conductor. Partial discharges occur when the local electrical field intensity exceeds the dielectric strength of the dielectric involved, resulting in localized ionization and breakdown. Therefore, measurement and analysis of this discharge can provide an early warning of insulation failures in equipment. Tests are supposed to anticipate stresses under service conditions and to reveal weak points. Such a means of quality check without doing harm by its application is the partial discharge measurement. This work presents a measuring system for PDs under impulse voltage. Based on a coupling device adapted for this kind of voltages and a method for removing contributions from the applied voltage. The potential of the system has been demonstrated through measurements of PDs around a needle to plane in air under lightning impulse and switching impulse voltages The observations obtained with this PD source prove that the measuring technique described enables detailed studies of PD properties under lightning and switching impulse voltages. This paper presents the characteristics of PD with the needle to plane in air under the impulse voltage in the laboratory.