Characteristic of partial discharge in air gap model of oil-paper insulation under DC voltage

The air gap of the insulation system is the main source caused partial discharge (PD) in high voltage power equipment made of oil-paper insulation material. In general, there are two kinds of air gaps, which come out from solid insulation-paper board because of manufacture process and liquid insulation-bubbles in oil. To investigate the characteristic of PD in oil-paper insulation under direct current (DC) voltage, this paper presents the air gap model of paper board and bubbles model in oil with oil-paper insulation system respectively. The partial discharges of these models are measured by Rogowski coil and sampling resistor under direct current voltage in the laboratory. The partial discharge pulses are analyzed and processed by Origin software such as frequency spectrum and filtering. The characteristic of PD pulses of the air gap in oil-paper under DC voltage are described in the end. These results lay the foundation for the PD measurement and recognition in oil-paper insulation system (such as converter transformer) under DC voltage.