Abstract
Corona discharge, an inevitable phenomenon, may lead to insulation degradation, threatening the safe and reliable operation of gas-insulated power equipment. The pulse stage is a complex but usual discharge process in corona discharge. In this paper, we investigate the pulse characteristics of negative corona discharge in a needle-to-plane electrode configuration in SF6/N2 gas mixtures under DC voltages. With an increase in mean current, a stage transition phenomenon from the Townsend stage through the pulse stage to the breakdown stage is observed. The variation in pulse amplitude and pulse time characteristics at the pulse stage is analyzed. In addition, the effects of gas pressure, gap spacing, and N2 content on onset voltage and pulse characteristic parameters, including pulse time parameters and the pulse repetition rate, at the pulse stage are presented. The results show that the current pulses mainly exhibit an irregular distribution of small amplitude. The pulse time parameters are not affected by gas pressure, gap spacing, or N2 content at pressures higher than 0.1 MPa. The pulse repetition rate decreases with an increase in gas pressure and N2 content but is only weakly affected by gap spacing, ranging from 1 kHz to dozens of kHz.
Highlights
In recent years, with the rapid development of DC technology, gas-insulated power equipment with SF6 or SF6/N2 gas mixtures as an insulating medium has received extensive attention in the field of DC transmission engineering.1–3 In practical SF6/N2 gas-mixture-insulated power equipment, the existence of metal protrusions inside the equipment produces an extremely inhomogeneous electric field, resulting in partial discharge, inducing corona and leading to insulation deterioration.4 It is difficult to avoid such corona because gas-insulated power equipment usually operates in high electric fields.The main factors affecting the pulse characteristics of corona discharge are gas pressure, gas composition, gap spacing, the curvature radius of the electrode, and applied voltage polarity
This paper focuses on the pulse characteristics and the most important influencing factors of negative corona discharge in SF6/N2 gas mixtures
The following conclusions can be drawn: (1) Negative corona discharge in SF6/N2 gas mixtures under different φ(N2) can be divided into three stages—the Townsend stage, pulse stage, and breakdown stage
Summary
With the rapid development of DC technology, gas-insulated power equipment with SF6 or SF6/N2 gas mixtures as an insulating medium has received extensive attention in the field of DC transmission engineering. In practical SF6/N2 gas-mixture-insulated power equipment, the existence of metal protrusions inside the equipment produces an extremely inhomogeneous electric field, resulting in partial discharge, inducing corona and leading to insulation deterioration. It is difficult to avoid such corona because gas-insulated power equipment usually operates in high electric fields. Cernák et al. carried out a detailed experimental analysis on a negative corona pulse and secondaryelectron emission during pulse development in 30%SF6/70%N2 gas mixtures at low pressure. They confirmed the existence of field emission during the Trichel pulse, and the experimental results verified the classic stepped-pulse theory of Morrow.. Kúdelcík et al. studied the effects of different cathode surface attachments on the photoemission coefficient and secondaryelectron emission, based on Cernák’s research They believed that the stepped-pulse depended on secondary photoemission processes and the peak of the pulse was the result of a cathode-directed streamer. We hope this study can provide a better understanding of the pulse characteristics of negative corona discharge in SF6/N2 gas mixtures
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