Partial Discharge Characteristics of SF6 and SF6/N2 in Nonuniform Electric Field Under Negative DC Voltage

In this study, the partial discharge (PD) characteristics of nonuniform electric fields in SF6 and SF6/N2 gases from PD inception to intermittent breakdown under negative dc voltage were systematically studied. The effects of the gas mixture ratio and electric field distortion on the PD characteristics were analyzed in terms of PD inception voltage (PDIV), PD amplitude, PD repetition frequency, and time-resolved PD (TRPD) patterns. The PDIV of SF6/N2 was higher than that of SF6 within a certain range of gas mixture ratios, which is related to the degree of electric field distortion. The greater the degree of electrical field distortion, the greater the range of gas mixing ratios, in which the PDIV of SF6/N2 was higher than that of SF6. The difference in the value of PDIV also increased with an increase in the degree of electrical field distortion. The PD amplitude and PD repetition frequency in SF6/N2 gradually increased with increasing applied voltage. Moreover, the smaller the SF6 content, the greater the PD amplitude and repetition frequency. In SF6, the PD amplitude significantly increased and the PD repetition frequency significantly decreased when the applied voltage increased to a high value. The shape features of the TRPD patterns in both SF6 and SF6/N2 changed with an increase in the applied voltage, but the change in SF6 was more obvious than that in SF6/N2.