Surface Discharge Voltage Research Articles

Influence mechanisms of ultraviolet irradiation aging on DC surface discharge properties of silicone rubber in dry and humid air

In the modern DC electrical transmission system, high-energy photons interact with silicone rubber (SIR) chains during long-term ultraviolet (UV) irradiation, it degrades the surface properties and triggers surface discharge (flashover) along the SIR-air interface, threatening the secure operation of the advanced electrical equipment. To further comprehend how UV-aging influences the flashover performance, in this work, the chemical bonds, surface charge transport parameters, and flashover performance of UV-aged SIR samples are characterized, and the influence mechanisms of UV-aging on surface discharge in dry and humid air are comprehensively clarified through the investigation from “molecular-mesoscopic-macroscopic” scales. The results indicate both degradation and oxidization reactions occur during UV-aging. The degraded molecular chains dominate the discharge in dry air, while oxidization reactions determine the discharge in humid environment: The degradation reactions reduce the surface trap depth and increase surface conductivity, leading to large surface leakage current and surface charge dissipation rate, causing flashover voltage in dry air increases and decreases as UV-aging time increasing. The oxidization of the chains introduces –OH and –COOH groups into chains, enhancing permittivity and adsorbing H2O molecules, significantly increasing surface leakage current, causing surface discharge voltage in humid air to decrease as UV-aging time increases.

Discharge Characteristics and Numerical Simulation of the Oil–Gas Surface under DC Voltage

Low insulation strength at the oil–gas surface due to oil leakage and partial discharge of oil-immersed power equipment is a major threat to the safe and reliable operation of power systems. This paper investigates the initiation and development of the oil–gas surface discharge. The oil–gas surface discharge test platform was established, and discharge tests were carried out at different gap distances (1–2.5 mm). By coupling the electric field and flow field, the multi-layer dielectric discharge streamer model was built, and the characteristics of charge and electric field distribution at different gap distances were studied. The test results show that the liquid surface between the electrodes rises during the discharge process. Furthermore, the surface discharge voltage exceeds the air gap discharge voltage. With the simulation analysis, the oil–gas surface discharge is a typical streamer development process. Under 50 kV applied voltage and 2.5 mm gap distance, the average development speed of the streamer is 12.5 km/s. The larger the gap distance is, the greater the average streamer development speed is. The recording and numerical simulation of the discharge process are of great significance for exploring the mechanism of oil–gas surface discharge, optimizing the discharge process, and diagnosing partial discharges.

Study on the Discharge Characteristics along the Surface and Charge Movement Characteristics of Insulating Media in an Airflow Environment

The gas–solid interface of high-voltage insulating equipment is a weaker part of insulating equipment insulation, and preventing the occurrence of discharge along the surface of insulating equipment is a critical problem for high-voltage insulation. This article investigates the discharge characteristics and charge movement characteristics of insulating media under an airflow environment. The surface discharge characteristics of the insulating medium in the airflow environment were obtained by using a high-velocity airflow test platform, and the surface discharge voltage characteristics, discharge path characteristics, and force conditions of the discharge process were analyzed. The surface charge motion characteristics of the insulating medium in the high-velocity airflow environment were also tested, and the distribution characteristics, dissipation characteristics and conduction mechanism of the surface charge of the insulating medium in the high-velocity airflow environment were revealed. The research results showed that: the discharge voltage along the insulating medium surface gradually increases with the increasing velocity of airflow; the discharge path along the surface of the insulating medium gradually shifts backward under the action of airflow; under the action of airflow, the charge on the insulating medium surface is blown away, thus reducing the charge concentration on the insulating medium surface; the trap level center of the insulating medium gradually decreases under the action of airflow, which provides the conditions for the charge blowing effect on the insulating medium surface. This investigation supplies the theory support for the protection of insulation equipment in an airflow environment and technical guidance for the insulation design of insulating equipment in an airflow environment to ensure the secure and steady running of insulating equipment in high-speed trains and high-voltage transmission lines.

Effect Mechanism of Surface Roughness of Solid Dielectrics to Surface Discharge Voltage in Liquid Nitrogen Under Lightning Impulse

The surface discharge of solid dielectric in liquid nitrogen has become one of the key problems in the development of high-temperature superconducting power devices. It is necessary to study the mechanism of surface discharge of the solid dielectric in liquid nitrogen. This article chose polytetrafluoroethylene and DW-3 epoxy resin as specimens, tested the surface discharge voltages of two kinds of specimens with different surface roughness under lightening impulse voltages in liquid nitrogen, and discussed the effect mechanism. The experimental results showed that the surface discharge voltage and discharge time of both materials in liquid nitrogen increased as the surface roughness increasing under lightning impulses. The surface roughness affects the surface discharge voltage of the solid dielectric in liquid nitrogen under lightning impulse, mainly in the charge left on the grinding surfaces of solid dielectrics, the heights of projections, and the creepage distance on the dielectric surfaces. The main discharge process is in the gasification path, and the effect of solid dielectric on surface discharge in liquid nitrogen is smaller. These reasons make the surface discharge in the liquid nitrogen less affected by the surface roughness. The results further explore the characteristics of surface discharge in liquid nitrogen and could provide methodological guidance to improve the surface discharge voltages in liquid nitrogen.

Plasma-Assisted Control of Supersonic Flow over a Compression Ramp

This study considers the effect of an electric discharge on the flow structure near a 19.4° compression ramp in Mach-2 supersonic flow. The experiments were conducted in the supersonic wind tunnel SBR-50 at the University of Notre Dame. The stagnation temperature and pressure were varied in a range of 294–600 K and 1–3 bar, respectively, to attain various Reynolds numbers ranging from 5.3 × 105 to 3.4 × 106 based on the distance between the exit of the Mach-2 nozzle and the leading edge of the ramp. Surface pressure measurements, schlieren visualization, discharge voltage and current measurements, and plasma imaging with a high-speed camera were used to evaluate the plasma control authority on the ramp pressure distribution. The plasma being generated in front of the compression ramp shifted the shock position from the ramp corner to the electrode location, forming a flow separation zone ahead of the ramp. It was found that the pressure on the compression surface reduced almost linearly with the plasma power. The ratio of pressure change to flow stagnation pressure was also an increasing function of the ratio of plasma power to enthalpy flux, indicating that the task-related plasma control effectiveness ranged from 17.5 to 25.

Surface Discharge Property of Polypropylene/BN Nanocomposite for HTS Apparatus Application

Surface discharge can lead to the failures of insulation materials in LN2, especially when the bubbles are generated during the quenching process. In this paper, the surface discharge properties of polypropylene (PP)/boron nitride (BN) nanocomposites were investigated in the normal and quench conditions. The results showed that the surface discharge voltage was improved in the normal condition as the BN filler content was increased from 5 wt% to 10 wt%. But it was reduced as the BN filler content was 15 wt%. As the filler content was less than 10 wt%, the free charges were captured by traps, which were with deeper trap energy level. In quench condition, the bubbles were decreased as the BN filler content increased, which were associated with the higher thermal conductivity of BN to rapidly release the joule heat. Therefore, the surface discharge voltage was increased with the BN filler content. The research has the potential to restrain the surface discharges and extent the lifetime of insulation materials in high-temperature superconducting devices.

Temperature‐dependent surface charge and discharge behaviour of converter transformer oil–paper insulation under DC voltage

Ambient temperature has significant influence on properties of oil–paper insulation, which makes surface discharge process complex. This paper aims at revealing the influence mechanism of ambient temperature on surface charge and discharge behaviours under DC voltage. The oil–paper with thickness of 0.08 mm was used and the ambient temperature varies from 20 to 80°C in this paper. The results of surface potential decay (SPD) experiments show that the initial surface potential declines and the process of SPD is accelerated with increasing temperature because of higher carrier mobility. Additionally, both shallow and deep trap energy level become deeper, the shallow trap density is enlarged while the deep trap density is shrunken at higher temperature. The surface discharge tests were performed and Weibull results indicate that it is prone to occurring surface discharge at higher ambient temperature. The possibility of surface discharge under negative voltage is larger than that under positive voltage because of polarity effect. It is concluded that more carriers escape from deep traps to participate in the procedure of surface discharge at higher temperature, which declines the surface discharge voltage.

Study on Surface Discharge Test of Combination of Insulating Shielding Covers for Live Working

In the distribution network live working, in order to improve the insulation protection area, insulation shielding covers are often used in combination. In this paper several common insulating shield appliance, surface discharge tests were carried out. The surface discharge test uses a ball-rod electrode to simulate field operation conditions and observe the discharge path with a high-speed camera. The test results show that the material types of insulating masks have a great influence on the surface insulating properties, the insulating properties of rubber masks and plastic masks are close, and the surface insulating properties of resin masking utensils are lower. Resin insulation blanket used in combination, overlapping parts of the more closely fit. When the overlap length is 15 cm, the surface discharge voltage in the overlap region of the resin insulating blanket is close to that of the rubber blanket. Considering the maximum operating voltage of 10kV distribution line is 11.5kV, the length of the overlapping parts is not less than 5cm.

Insulation structure design of the UV-preionization gas switch

The insulation structure of the UV-preionization gas switch for LTDs (Linear Transformer Drivers) has been designed in this study. The surface discharge along the gas switch chamber surface problem has been studied to ensure the gas switch can be charged to 200 kV DC. Meanwhile, the structure of the gas switch ought to be designed compact, in order to lower the overall inductance of the UV-preionization gas switch for LTD. It has been found that surface discharge is most likely to occur at the connection part of the solid dielectric, the electrodes and the air according to the electric field intensity simulation by a two-dimensional electrostatic solver. Polycarbonate (PC) has been selected as the insulator for the gas switch by analyzing the electric field distortion extent and the machinery strength of the various kinds of insulators. A surface discharge experiment has been designed. The experiment measures the surface discharge voltage in various distinct conditions of the surface roughness, the surface discharge distance and the gas pressure etc. In analogy to the air breakdown voltage empirical formula (U=f(pd)), we fitted the surface discharge voltage formula for the product of surface discharge distance and the gas pressure. The chamber surface has been grooved since the surface discharge distance has to be lengthened. It has been found that the measure of raising the grooving width is more effective than the measure of raising the grooving length in preventing the surface discharge when comparing the experimental results of these two different grooving methods.

Surface Discharge Characteristics of GFRP in GN2and LN2for Designing a Superconducting Coil System

Solid insulation materials used in the application of a superconducting apparatus need to be robust in terms of both mechanical and dielectric performance. The surface discharge characteristics of solid insulation materials are inferior to their penetration breakdown characteristics. Therefore, dielectric accidents in a superconducting appliance can occur as a form of surface discharge rather than as a form of penetration breakdown. In this paper, dielectric experiments on the surface discharge characteristics of glass-fiber-reinforced plastic in gaseous nitrogen (GN2) at room temperature and liquid nitrogen (LN2) at 77 K are conducted to design a high-voltage superconducting coil system with high reliability. As a result, the electric field intensity at surface discharge voltage $V_{\mathrm{SD}}$ under ac and dc voltages is deduced as an empirical formula.

Characteristics of induced discharge on a polymer insulator surface under electro-wetting conditions

In this paper, laboratory experiments were conducted to investigate the precipitation characteristics and induced surface discharge on polymer insulator specimens under electro-wetting conditions simulated by artificial fog-wetting conditions at different operating voltages. Based on image processing methods, quantitative analysis was carried out on precipitation parameters to obtain the deposited amount, relative distribution area, statistics of droplet size distribution and distributed droplet box dimension in relation with the duration of precipitations and operating voltages. Also, the onset voltage of surface discharge and flashover voltage were measured for the purpose of establishing the influence of the obtained precipitation parameters on the surface discharge. It was found that the precipitation process is in a dynamic balance between fog deposition and droplet evaporation, and is significantly affected by the type and level of operating voltage. Operating voltage increase results in a relatively lower deposit amount and distributing area of water droplets. There are further reduced when the precipitating duration is increased at higher voltage level. The smallsize ( 2 mm) droplets increase with increasing AC operating voltage, but do not appear significantly under high ±DC operating voltage. When precipitation duration is increased, box dimension of droplet distribution under nonand low- operating voltage shows tendency to increase, but tendency to decrease under high operating voltage. Finally, a relationship between the onset voltage of surface discharge, the flashover voltage and the droplet distribution parameters was established, showing that the increasing precipitation regularity of water droplets on the polymer insulator specimen surface can induce more likely occurrence of surface discharge, even flashover.

친환경 절연가스 중 연면절연성 향상을 위한 고체유전체의 유전율과 지름에 따른 연면방전특성 연구

This paper studied surface discharge characteristics by a dielectric constant and diameter of solid dielectrics in N2/O2 mixture gas. Applied electric field strength at N2/O2 mixture gas was changed from the dielectric constant and diameter of the solid dielectrics, and insulation performance of the N2/O2 mixture gas determined surface discharge voltage. In each of the diameter at the solid dielectrics, the surface discharge voltage was increased by lengthening surface distance, whereas increasing rate of the surface discharge voltage was different from gas pressure. Thus, In this paper, main factors of surface discharge are as follows. 1) Insulation performance of N2/O2 mixture gas, 2) Dielectric constant of solid dielectrics, 3) Surface discharge path. It was clear that the surface discharge voltage depend on the main factors. These results will be applied to useful data for an eco-friendly composite insulation design.

친환경 절연설계를 위한 N2/O2혼합가스 중 고체유전체 종류에 따른 연면방전특성

In this paper, we deal with a surface discharge that caused an aggravation of the dielectric strength in the mixture gas, When composit dielectrics were formed from the use of a solid dielectric. It was found from this study that the surface discharge voltage was deeply involved in the mixture ratio of , the electrical property of the solid dielectric, kind of the solid dielectric, an electric field at the triple junction and a medium effect. These results expect basic data that will be used to transmission and distribution power system equipment using the mixture gas.

The Insulation Evaluation of N2:O2Mixture Gas

With the improvement of industrial society, high quality electrical energy, simplification of operation and maintenance, and ensuring reliability are being required. Also we request an urgent change from SF? gas to an environment-friendly gas insulation material. In this paper, the experiments of breakdown characteristics by pressure and gap change of N₂/O₂ mixture gas through a GIS (Gas Insulated Switchgear) model were described. This paper reviews basic data of the surface discharge characteristics for Teflon resin in not only pure N2, N₂:O₂ mixture gas as being focused on environmentally-friendly insulating gas, but also SF?. Also, insulation characteristics by breakdown voltage and surface discharge voltage of N₂:O₂ mixture gas in the experimental chamber were studied.

Dry-Air 중의 전극 형상 및 에폭시수지의 크기변화에 따른 연면방전특성 연구

This paper shows a basic data of the surface discharge characteristics for epoxy resin in Dry-Air as being focused on environmentally friendly insulating Gas. Used electrodes are needle to plane, sphere to plane and KS M3015 electrodes. With the changing electrodes in same condition, we can obtain different creeping lengths, surface discharge voltages and surface dielectric strengths, respectively. Surface dielectric strengths of Needle to plane electrodes are more higher than the others. Moreover, it is considered that the surface discharge characteristics with variation of epoxy resin thickness and diameter. Surface discharge voltage increases as the thickness and the diameter of epoxy resin.