Abstract
Under DC voltage, charge accumulates on the break insulation of mechanical DC circuit breakers, distorting the local electric field, which increases the risk of break insulation failure. Glass-fiber vacuum-impregnated epoxy resin can be used as an insulation material for DC circuit breakers owing to its excellent mechanical and electrical properties. We have created a system to measure the surface potential of an epoxy resin in different gases. The accumulation and dissipation of the surface charge in air and SF6 are determined, and the effects of air and SF6 are compared. The results show that the polarity of the surface charge is the same as that of the applied DC voltage, and that the main source of the charge is from Schottky charge injection. In SF6, the charge density is higher than that in air, and its decay rate is slower. The decay law of the surface potential in SF6 can be characterized by two exponential superposition formulas. In the early stage, surface charge is attenuated mainly by being transferred along the surface of the insulator and neutralized by gas ions. In the late stage, surface charge is attenuated mainly by transferring through the volume of the insulator.
Highlights
In recent years, high-voltage DC transmission technology has increasingly been applied to longdistance, high-capacity power transmission and power system interconnections.[1]
The simulation showed that when the voltage was −15 kV, the maximum electric field strength near the anode was 33 kV/cm, which was bigger than the breakdown electric field strength (30 kV/cm) in air
Partial discharge occurred near the anode triple junction (ATJ), which generated charged particles. (Here the ATJ was the junction of the anode, dielectric, and air.) The positive charges moved toward the solid insulation medium because of the normal electric field, and the negative charges moved in the opposite direction (Figure 4(b)), which caused an accumulation of positive charges near the anode
Summary
High-voltage DC transmission technology has increasingly been applied to longdistance, high-capacity power transmission and power system interconnections.[1]. Research has shown that when a DC voltage is applied, charge accumulates at the surface of the solid insulation medium of the break in the DC circuit breaker. As the applied voltage increases, the density of the surface charge decreases gradually and tends towards being stable.[8] Different electrode structures have different electric field distributions on the surface of the insulation medium, which affects the accumulation and dissipation of the surface charge. The tangential electric field affects the transfer characteristics of the charge, which changes the surface charge distribution.[9] The accumulation and dissipation of the surface charge on the insulating medium can be improved by optimizing the electrode structure and by surface fluorination,[10] ray irradiation,[11] plasma treatment[12] and nanoscale modification.[13]. We analyze how the voltage amplitude affects the charge injection and investigate how the gas pressure affects the surface charge decay
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