Variability of the Electrical Signals Generated by PDs in Mineral Oil under Long-term AC Voltage

This paper presents research that deals with analysis and assessment of potential variability of the electrical signals generated by partial discharges (PD) phenomenon while continuous AC voltage is applied within a long period. Several selected physical quantities are investigated in order to indicate any potential trends. The electrical method for the apparent charge measurements on PD is applied. The PD source (PDS) that generates surface discharges (SD) is placed inside of the steel tank filled with new mineral transformer oil. A ceramic-glass plate is used as a solid dielectric barrier placed between the high voltage and grounded electrodes. A continuous AC voltage is applied for powering the PDS within 144 h. The voltage level is constant during all measurements and its relative level is 1.3 of the inception voltage (U
_i
) of the PDS. Signals emitted by the continuously occurred PD are captured and investigated. On the grounds of the descriptor analysis some long-term characteristics of the applied PDS in new transformer oil are presented. Finally some selected statistical tools are applied for the results analysis and presentation. Also simple regression models are proposed for the selected descriptors to discover some trends of their variability. Presented results potentially allow to be applied for modeling of the PD variability in time. Furthermore such an approach may potentially support the development and extend the abilities of the diagnostic tools and maintenance policy in electrical power industry.