Partial Discharge of Needle-Plane Defect in Oil-Paper Insulation under AC and DC Combined Voltages: Developing Processes and Characteristics

Abstract

Partial discharge (PD) behaviors of oil-paper insulation is distinctive in AC and DC combined electric fields in converter transformers from PD behaviors in pure AC or DC electric fields. The present study focuses on the PD developing processes and characteristics of oil-paper insulation systems with needle-plane defects under different AC/DC proportions. The degradation of oil-paper insulation can be accelerated by PD pulses incurred by needle-plane defects. AC-DC combined voltages are applied to the needle-plane defect model simultaneously in the established experimental platform, and the proportions of AC/DC voltages are decided according to the cases in actual converter transformers. The developing processes from the initiation of partial discharge until final breakdown were observed for each AC/DC proportion. PD parameters and patterns were acquired by a detector using the pulse current method. The test results indicate that the inception and breakdown voltages increase with the increase of the DC component in AC-DC combined voltages. However, pulse repetition rate and amplitude of PD shows a descending trend when AC/DC proportion decreases. Meanwhile, the PD recurrence rate in the phase between 180 • and 360 • becomes higher than that in the phase between 0 • and 180 • at the initial stage as the DC proportion increases; high-amplitude discharges mainly occur in the phase range between 180 • and 360 • when the pressboard is close to breakdown. The current study is useful in further research on fault diagnosis in converter transformers.

Effect of aging on material properties and partial discharge characteristics of insulating pressboard

“…Oil-paper insulation is the main form of internal insulation in power transformers (Harbaji et al 2015;Xia and Wu 2016;Chen et al 2017;Hao et al 2018). There is much research available on the aging of oil-paper insulation and the factors that affect PD (Zhou et al 2015;Wei et al 2016a;Xie et al 2016a;Sun et al 2017;Munajad et al 2018). Mitchinson et al (2008) designed a model for point discharge and investigated the effects of voltage and time on oil-paper insulation.…”