Surface Charge Accumulation Behaviors Research Articles

The Effect of a Metal Particle on Surface Charge Accumulation Behavior of Epoxy Insulator with Zoning Coating

Epoxy insulators are widely used in Gas-Insulated Transmission Lines (GILs), playing a significant role in electrical insulation and mechanical support. The metal particles generated during the production and operation of the equipment aggravate surface charge accumulation on the insulator, causing surface flashover. Therefore, it is necessary to study the suppression strategy of charge accumulation. In this paper, a downsized disc insulator was taken as the research object to investigate the effect of zoning coating on charge suppression with the presence of a linear aluminum metal particle under negative DC voltage. The zoning coating method was achieved by painting coatings with different conductivities in three areas on the insulator surface to regulate the charge. The inhibition mechanism of zoning coating on the charge accumulation in the presence of a linear metal particle was analyzed with the assistance of numerical simulation. The results showed that negative charges were accumulated in the nonplanar region as there was no metal particle, and the existence of metal particles led to the significant accumulation of positive charge speckles in the nonplanar region. The application of zoning coating could significantly inhibit the charge accumulation in the nonplanar area of the insulator and the charge injection from the grounded electrode to reduce the charge density. Under −25 kV, the maximum charge density on the insulator with the zoning coating was 48.1% lower than that without the coating, and the inhibition effect increased by 57.9% when the metal particle was introduced. This paper provides a new way to suppress the charge accumulation on the insulator surface.

Metal particle encouraged surface charge accumulation on epoxy insulator with multi-arc surface profile under DC voltage

Surface charge accumulation on epoxy insulator installed in gas insulated switchgear (GIS) or gas insulated transmission line (GIL) has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on surface charge accumulation behavior on a actual epoxy insulator for 100 kV GIL prototype with multi-arc surface profile. A coaxial electrode system is used to investigate the charging behavior under DC voltages with metal particles positioned at various positions of the surface so as to estimate its influence on the charge accumulation behavior using a Kelvin type probe. The results show that positive charges are accumulated mainly on the nonplanar region around the high voltage electrode in the shape of speckles, and the average charge distribution along the radial direction presented a double-peak feature. Moreover, the charge accumulation is enhanced by metal particles contacting to the grounded electrode. Using a numerical simulation method, it is suggested that the charge accumulation is mainly determined by gaseous ionization which is enhanced by the metal particle induced electric field distortion.

Mechanism Analysis of Particle-Triggered Flashover in Different Gas Dielectrics Under DC Superposition Lightning Impulse Voltage

When DC GIL in operation endures the lightning impulse voltage, the charge accumulation at the gas-solid interface area will seriously affect the insulation performance of the spacer. Considering that gas side conduction is one of the important factors affecting charge accumulation, for the purpose of clarifying of the insulation characteristics of gaseous medium in the flashover process of gas-solid interface, an experimental platform for simulating the working conditions of the spacer is built. The spacer flashover tests were carried out with and without aluminum particle in SF6, 4% C3F7CN /96% CO2 and 20% SF6/80% N2 gas mixture. The measurement and analysis of surface potential distribution behavior of the spacer was conducted. The experiment results show that the gas dielectric is not the factor which dominate the potential distribution process without aluminum particle, and there is little difference in potential distribution with various gaseous conditions. When the linear aluminum particle appears on the surface of the insulator, it will cause severe electric potential distortion and these potential distorted areas are located around the end of the metal particle near the central conductor, and along with flashover pathway. It has also demonstrated that the gaseous dielectric has influence on the surface charge accumulation behavior especially with metallic particle adhere to spacer surface. Under the C3F7CN/CO2 gas mixture, the surface flashover voltage decrease percentage is about 16.82% and may be lower. Besides, the insulation strength of the gaseous dielectric itself is also a key factor affecting flashover.

Magnetic field induced variation in surface charge accumulation behavior on epoxy/Al2O3 nanocomposites under DC stress

Surface charge accumulation on epoxy based nanocomposites under DC stress with and without the presence of a magnetic field was investigated in this work. Two mm-thick sheet samples were prepared by adding 60 nm-Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> particles into epoxy with filler content of 1 to 5 wt%. A pair of finger-shaped electrodes was employed to introduce electric charges onto the sample surface under DC stress of ±5 and ±10 kV. The magnetic field was established by using a pair of permanent magnets, by which a magnetic flux density of 100 and 180 mT was achieved. Surface charge between the electrodes was measured by means of a Kelvin type electrostatic voltmeter, and the influence of nano-filler content and magnetic flux density on charge distribution as well as charge density was estimated. The results indicate that increasing nano-filler content from 0 to 5 wt%, the average charge density increased initially then decreased. The presence of a magnetic field results in a deflection of charge profile as compared with that formed without a magnetic field. The charge density increased as the magnetic flux density increased from 0 to 180 mT. It is suggested that the charge trajectory close to high voltage electrode varies by the combined electric-magnetic force, by which electric field recovery in such a region is facilitated thus more charges are encouraged to accumulate on the surface.

Magnetic field induced variation in surface charge accumulation behavior on epoxy/Al2O3 nanocomposites under DC stress

Surface charge accumulation on epoxy based nanocomposites under DC stress with and without the presence of a magnetic field was investigated in this work. Two mm-thick sheet samples were prepared by adding 60 nm-Al 2 O 3 particles into epoxy with filler content of 1 to 5 wt%. A pair of finger-shaped electrodes was employed to introduce electric charges onto the sample surface under DC stress of ±5 and ±10 kV. The magnetic field was established by using a pair of permanent magnets, by which a magnetic flux density of 100 and 180 mT was achieved. Surface charge between the electrodes was measured by means of a Kelvin type electrostatic voltmeter, and the influence of nano-filler content and magnetic flux density on charge distribution as well as charge density was estimated. The results indicate that increasing nano-filler content from 0 to 5 wt%, the average charge density increased initially then decreased. The presence of a magnetic field results in a deflection of charge profile as compared with that formed without a magnetic field. The charge density increased as the magnetic flux density increased from 0 to 180 mT. It is suggested that the charge trajectory close to high voltage electrode varies by the combined electric-magnetic force, by which electric field recovery in such a region is facilitated thus more charges are encouraged to accumulate on the surface.

Surface charge accumulation behavior and its influence on surface flashover performance of Al2O3-filled epoxy resin insulators under DC voltages

Surface charge accumulation on insulator surface can have great influence on surface flashover performance. An experimental system is established to investigate surface charge accumulation and decay characteristics of Al2O3-filled epoxy resin insulators in 0.1 MPa SF6 under DC voltages. Surface potential is recorded by a Kelvin vibrating probe connected to an electrostatic voltmeter. By pre-depositing charges on insulator surface, the influence of surface charges on surface flashover performance is studied. The results reveal that surface charge distribution appearance is the combined effect of electrode injection, back discharge and gas ionization. Surface charge distribution has obvious polarity effect. It is concentrated near the HV electrode under positive voltages and dispersed under negative voltages. The difference in positive and negative surface flashover voltage is attributed to the difference in surface charge distribution under DC voltages of different polarities. Surface charge decay contains two stages, which satisfies the law of double exponential function. At first stage, surface charge decays fast, which corresponds to charges escaping from shallower traps. While it decays slowly at the second stage, which corresponds to charge escaping from deeper traps. Surface charge decay process is dominated by surface conductivity mechanism. The pre-deposited charges on insulation surface have great influence on surface flashover performance. The deposited positive charges can increase positive flashover voltage but decrease negative flashover voltage.

Effects of surface roughness on surface charge accumulation characteristics and surface flashover performance of alumina-filled epoxy resin spacers

The accumulated charges on the insulator surface become a key factor to incur surface flashover. The charge accumulation process is closely related to the surface condition. This research investigates the effects of surface roughness on surface charge accumulation behavior and surface flashover performance of alumina-filled epoxy resin spacers in SF6/N2 mixtures under DC voltage. The insulator is prepared with only half surface subjected to rough treatment. The accumulated charges are distributed in two regions. Considerable homo-charges are located near the high voltage (HV) electrode and few hetero-charges are near the grounded (GND) electrode (region I). These charges are injected by electrodes. The bipolar charges between HV and GND electrodes (region II) originate from gas ionization. Surface rough treatment can suppress surface charge accumulation and improve surface insulation strength. When increasing surface roughness, surface charge declines first slowly (stage I) and then rapidly (stage II), which coincides with the two stages of surface flashover voltage increment. Surface charge declination at stage I is mainly due to the increase in surface conductivity, while at stage II, the introduced deep traps also play a role. Surface flashover voltage increment at stage I is mainly due to the extended creepage distance, while at stage II, the declination of surface charge also plays a role. Besides, the block of electron avalanche development by the roughed surface is also responsible for the increase in surface flashover voltage at these two stages.

Experimental investigation of surface charge accumulation behaviors on PTFE insulator under DC and impulse voltage in vacuum

Surface charge accumulated on insulators plays an important role in flashover process in vacuum, which has not yet been fully understood. In this paper, charging behaviors on insulator surface were experimentally examined under negative DC and impulse voltage. For the case of DC voltage, two charging stages were observed, i.e., the area near cathode was at first negatively charged under lower voltage (stage I) and then followed by a positively charged cathode-anode surface (stage II). Surface charging at stage I is considered to be caused by Schottky injection of homo-charges from electrode into sample surface layer. While at stage II secondary electron emission (SEE) process is responsible to the positively charged anode-cathode surface. However, charging at stage I is quite sensitive to pre-stress process, as well as the electrode-insulator interface conditions. The ongoing injection of electrons from cathode can lead to gradually decreasing in surface charge accumulation as the voltage duration increases. For the case of impulse voltage, Schottky injection of homo-charges has little influence on surface charging as the time is too short for charge injection and migration in surface layer. The SEE process will govern surface charging due to its extremely fast establishment process. A good linear relationship is obtained between saturated surface charge density and applied voltage, which is generally consistent with the numerical calculation result based on secondary electron emission avalanche theory. At last, it is confirmed that the ionization of desorbed gas from insulator surface and subsequent neutralization of electrons with positive surface charge is the main cause to eliminate surface charge in flashover.