An Investigation of Negative DC Partial Discharge Decomposition of SF₆ Under Different Metal Materials

Abstract

For determine the influence of metal materials on the negative DC partial discharge (PD) decomposition of SF 6 and put forward for the method of SF 6 DC gas insulated equipment condition monitoring and fault diagnosis based on decomposed component analysis, this study investigates the decomposition characteristics of SF 6 under three common metal materials (Al, 304 stainless steel, and Cu) in gas insulated equipment by using SO 2 , SOF 2 , and SO 2 F 2 as characteristic component gases under negative DC PD. Results show that the types of metal materials have substantial effects on the negative DC PD decomposition characteristics of SF 6. The simulation results based on the first principles confirm the phenomena observed in the experiment: the amounts and generation rates of SOF 2 were the most abundant, followed by SO 2 F 2 and SO 2. The calculation based on free electron cloud and finite depth particle in a box model shows that the electron current density of field emission has the relationship with metal work function γ and electrical field E: j(0, E) ≈ (BE 2 /γ) exp(−Dγ 3/2 /E), where B and D is constants. The electron current density by field emission is inversely proportional to the work function of metal with constant electric field. The metal material with smaller work function means the greater electron current density, further promoting the decomposition of SF 6 to generate more characteristic component gases. The results can well explain the phenomena observed in the experiment, that is, the decomposition of SF 6 is the most serious under Al electrode with lowest work function, followed by 304 stainless steel, and Cu. INDEX TERMS Negative DC, metal materials, SF 6 , first principle, work function. I. INTRODUCTION With the development and trial operation of key ultra-high voltage DC (UHVDC) gas-insulated equipment, such as ± 800 and ± 1100 kV gas DC wall bushings [1]-[3], SF 6 DC gas-insulated equipment has been widely used in UHVDC power transmission projects [4], [6]. DC gas-insulated equipment has great advantages, such as simple and compact structure, light weight, and good heat dissipation [7]. However, harmful metal protrusion defects are inevitably observed in the production, transportation, installation, and operation of The associate editor coordinating the review of this manuscript and approving it for publication was Jenny Mahoney.

Design of Transmission Line and Electromagnetic Field Sensors for DC Partial Discharge Analysis

“…where θ2 and θ1 are the outer and inner electrode angles, respectively. Equation (2) shows that Z0 is determined by the ratio between center and outer electrode angles (θ1 and θ2) of the conical TL.…”

“…PD is one of the most chronic and unavoidable dielectric challenges that causes accelerated dielectric material aging and device failure. To name a few, the existence of metal particles in gas insulated substations (GIS) causes PD that lead to system failure by generating floating potentials, flashover, carbonization along spacers, and decomposition of gases [1,2]. In the cases of cables, bushing, and transformers that are electrically insulated mainly by solid and liquid insulators, the inevitable formation of air bubbles (in liquid) or cavities (in solid) during the manufacturing processes leads to the generation of internal PDs [3,4].…”