Flashover Voltage Research Articles

Flashover voltage of porcelain insulator under various pollution distributions: Experiment and modeling

The current work investigates the flashover voltage of an 11 kV porcelain insulator against changes in the location of the dry band, salt deposit density, humidity, non-uniform pollution degree, and polluted surface area. Generally, the flashover voltage of the polluted insulator dropped sharply compared to that of the clean insulator. Specifically, under salt deposit density (SDD) of 0.03 mg/cm2, the flashover voltages of scenarios A (full pollution), B (dry band 1), C (dry band 2), and D (dry band 3) decrease by 26%, 19%, 10%, and 2%, respectively, compared to 43.70 kV flashover voltage of the clean insulator. With an increase in SDD, the flashover voltage under all scenarios decreases steadily, with the median flashover voltage of scenario A being the lowest at 17.52 kV. The flashover voltage under all scenarios also varies with changes in the humidity level, non-uniform pollution degree and polluted surface area. Subsequently, an artificial neural network (ANN) and fuzzy logic (FL) hybrid model is proposed to predict the flashover voltage and condition of the insulator, where the model successfully yields the insulator condition index between 0 and 100% to indicate the pollution severity of the insulator.

Streamer Propagation along the Insulator with the Different Curved Profiles of the Shed.

The flashover along the insulator endangers the reliable operation of the electrical power system. The reasonable curved profiles of the shed could improve the flashover voltage, which would reduce power system outages. The research on the influence of the curved profiles of the shed on the streamer propagation along the insulator made of polymer was presented in the paper. The streamer propagation “stability” field, path, and velocity affected by the curved profiles of the shed, were measured by ultraviolet camera, ICCD camera, and photomultipliers. The “surface” component of the streamer is stopped at the shed with the different curved profiles, while the “air” component could go round the shed and reach the cathode. The streamer propagation “stability” fields are inversely proportional to the curved profiles of the shed. The streamer propagation velocities are proportional to the curved profiles of the shed. The relationship between the streamer propagation and the flashover propagation was discussed in depth. The subsequent flashover propagation is greatly affected by the streamer propagation path and “stability” field. Furthermore, the influence of the material properties on the streamer propagation path was also discussed in depth.

Radiation electron trajectory modulated DC surface flashover of polyimide in vacuum

Improving surface flashover voltage on vacuum-dielectric interface irradiated by electrons is a long-standing challenge for developing high-voltage and high-power spacecraft technology. The basic issue is understanding the role of radiation electrons in the process of surface flashover. In this paper, a ‘three-segment’ curve concerning the surface flashover properties under electron irradiation is discovered experimentally. As the gap distance of electrodes increase, the surface flashover voltage of polyimide during electron irradiation presents a trend of firstly increasing, then decreasing, and finally stabilizing. According to the simulation of the trajectory distribution for kinetic electrons, this trend is found to correspond with three typical stages respectively. In stage A, the kinetic electrons are completely deflected and the varying electrode parameters mainly affect the electric field distribution. In stage B, the kinetic electrons can irradiate the part of polyimide. The promoting effect of those electrons on flashover process enhance with the enlargement of the irradiated region. In stage C, trajectories are no longer seriously deflected and the role of kinetic electrons do not vary with electrode parameters. Combining with the results above, a model with combined effects of both kinetic and deposited electrons on surface flashover in vacuum is thus proposed, base on which the guidance for the methods of improving surface flashover voltage during electron irradiation is provided.

Flashover Voltage Prediction Models under Agricultural and Biological Contaminant Conditions on Insulators

The flashover performance of contaminated insulators highly depends on the type of pollutant and its present concentration. In this paper, important agricultural salts (NaCl, K2SO4, NaHCO3, CaSO4, KHCO3, MgSO4, NH4), 2Fe(SO4)2, and 6H2O (ferrous ammonium sulphate, dust, and urea) at different concentrations, and biological contaminants, such as algae and fungi, were taken as pollutants, and the AC flashover behavior of a porcelain-cap-and-pin-type insulator polluted with these two different pollutants was investigated. The experiment was carried out by a semi-natural method, wherein the insulator was first polluted artificially; thereafter, natural fog was applied to measure the wet flashover voltage. Test results indicated that the flashover voltages were affected by both soluble salts and non-soluble components deposited on the insulator surface. In the case of the thickly contaminated layers, non-soluble deposits greatly reduced the flashover voltage. Moreover, by using regression analysis, four empirical models based on different variables were developed. The empirical models developed in the present work represented a good degree of relation in predicting the flashover voltage of naturally contaminated insulators.

An Improved Dynamic Multi-Arcs Modeling Approach for Pollution Flashover of Silicone Rubber Insulator

This article presents a dynamic modeling approach to analyze pollution flashover of silicone rubber insulators. Pre-flashover conditions can be used to represent analytical formulations for different stages of dry band arcing activities on the surface of polluted insulator. In this article, effects of dust deposit as nonsoluble deposit density (NSDD) are investigated on the dynamic behavior of partial arcs on the surface of insulators by means of a proposed multi-arcs modeling approach. It is shown that analytical formulations of dynamic resistance of surface pollution can be used to analyze different modes of arcing as unstable and stable. Real data of leakage current (LC) and flashover voltage (FOV) of polluted insulator are used to make correlation with analytical multi-arcs formulations. The proposed analytical multi-arcs model is based on an artificial neural network (ANN) which is able to predict the LC and FOV of the insulator in real-time monitoring. In addition, effects of pollution resistance as variable surface conduction and thickness of pollution layer are investigated on LC and FOV of the insulators. It is shown that the proposed multi-arcs representation has a closer correlation with real testing data in comparison to previous single-arc and multi-arcs models.

Armature Ejecta and Its Effects on Insulator Degradation in Solid-Armature Launchers

Armature ejecta, which erodes the insulator and reduces surface dielectric strength, has been considered as a threat to solid-armature launchers. Two series of experiments were carried out in a small caliber launcher (SCL) to investigate the sources of armature ejecta and degradation mechanisms of the insulator. In first series of experiment, the ejection of armature was imaged by a high-speed camera. The influence of linear current density on ejection was studied in second series of experiment. Mass difference of insulator samples was used to evaluate the output of armature ejecta. Insulation performance was judged from the surface flashover voltage. And the degradation mechanism resulted from armature ejecta was analyzed based on the process of surface flashover. Results show that the local breakdown at armature–rail interfaces is one of the sources of armature ejecta. The amount of ejecta on samples increased with linear current density. Average flashover voltages decreased when ejecta increased in Zone A (0–200 mm) and Zone B (200–600 mm). And there was little difference of average flashover voltages in Zone C (600–900 mm). The discharge channel of the post-shot sample was composed of arcs and ejecta. The distortion of the surface electric field and the shorten of creepage distance are degradation mechanisms of bore insulators in solid-armature launchers.

Triple Point Surface Discharge Photography in Atmospheric Gases Using Intensified High-Speed Camera System

In this article, investigations of surface discharges using an ultraviolet (UV) intensified high-speed camera system are presented, accompanied by high-frequency response and resolution current recordings. A needle-plane electrode configuration is employed for the generation of a strongly nonuniform electric field on the surface of disk-shaped insulator samples made of polytetrafluoroethylene (PTFE) or epoxy resin. The electrode arrangement is further insulated by a gaseous medium of either technical air (21% O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /79% N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), nitrogen (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), or carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). An alternating (ac) voltage waveform at power frequency (50 Hz) is maintained at levels sufficiently below the flashover voltage corresponding to each presented case. Detailed descriptions of the technical specifications of the utilized equipment are provided for both optical and electrical measurements in the experimental setup. The obtained results demonstrate the discharge propagation during the ac-cycle and its dependence on the insulator type and gaseous insulating medium. Individual surface discharges are captured in the microsecond range to describe the discharge morphology based on the generated current pulse and instantaneous applied voltage level. Back-discharges on the insulating disk are also discussed, and relevant image capture is presented.

Determination of Breakdown Voltage Along the Surface of a Cylindrical Insulator

This article investigates the electric breakdown along the surface of a cylindrical dielectric, part of a coaxial transmission line. The particular geometry of the insulator is very common, as it is used at the input or output of most high-power, high-voltage (HV) generators. The streamer propagation criterion is used to calculate the flashover voltage. Studies of the dependence of the flashover voltage on the distance between the electrodes obtained in tests with dc voltage and also by applying voltage impulses with different durations and rise times are reported. The highest difference between the estimated values and the experimental data is less than 15%, which proves the applicability of the criterion for determining the surface breakdown voltage within the geometry under study. In particular, the results of these studies are used in the design of a compact 0.5-MV pulsed power system currently under development.

Metal-wire-embedded alumina insulating material using micro- and nanoscale 3D printing for surface flashover mitigation in a vacuum

A micro- and nanoscale 3D printing technique is applied to fabricate a functional insulating material that mitigates surface discharge in a vacuum based on microscopic electron multipactor suppression. The proposed alumina ceramic insulator design consists of surface-embedded thin metal wires that introduce a local gradient of secondary electron emission (SEE) yield, such that the trajectories of multipactor electrons are distorted by accumulated negative surface charge and the SEE avalanche across the insulator surface becomes intermittent. Considerable increases of surface flashover threshold and surface charging reduction are verified by the experiment. Also, additional efforts are made to determine the optimal size and spatial distribution of the metal wire. A convex-shape flashover voltage trace is observed when increasing the width of the wire, suggesting a trade-off between the multipactor mitigation and the insulator strength. The wire’s position between the adjacent cathode triple junction and the middle of the insulator is proved to be favorable for flashover mitigation. The physical details of surface flashover mitigation by the proposed insulator design are revealed by an ab initio particle-in-cell simulation code, corroborating the experiment from a microscopic aspect.

Linking trap to G10 surface flashover in liquid nitrogen under DC voltage

The insulation failure is a bottleneck to restrict the safe operation and development of direct current (DC) superconducting power devices. The solid–liquid flashover test is an important evaluation index, but the previous researches mostly focus on engineering application, and less involve in the mechanism analysis. As a characterization method for defects existing in the dielectric, the trap has been applied to the study of flashover to occur polymer surface in liquid nitrogen (LN2) in recent years. However, the mechanism of trap action in solid–liquid flashover is still confusing. Therefore, this paper carries out the following research. Firstly, the flashover voltage and current of glass epoxy laminate sheet (G10) in LN2 were obtained through experiments and analysis using the Weibull model in this paper. Secondly, the flashover process of G10 was monitored. The changes of G10 surface morphology and chemical bond before and after flashover were also observed. Finally, the relationship between polymer flashover and trap in LN2 was analyzed based on the surface trap distribution test and theoretical calculation of the charge transport equation. The results are beneficial to guide the selection and performance improvement of dielectric materials and the design of insulating structures in superconducting devices.

Fluorinated PEEK and XLPE as Promising Insulation Candidates for the Propulsion System of All-electric Aircraft

This article investigates the surface electrical properties of polyether-ether-ketone (PEEK) and cross-linked polyethylene (XLPE) before and after the fluorination modification. The samples are tested for surface conductivity, surface morphology, and surface antiaging characteristics. The samples are also tested for flashover voltage with ramping voltage under 100, 20, and 10 kPa. The results showed that the surfaces of PEEK and XLPE become slightly smoother with the increase in the fluorination time and the conductivity increased with the increase in the fluorination time. After fluorination, the surface of PEEK shows significant hydrophilicity, while the surface hydrophobicity of XLPE is slightly reduced, and there is a trend of recovery with the extension of the fluorination time. After fluorination, the surface antiaging performance is significantly improved. Compared with the untreated samples, the fluorinated PEEK has a higher flashover voltage at 100 kPa, and the flashover voltage is slightly increased at 10 and 20 kPa, while the flashover voltage of XLPE after fluorination shows a downward trend, especially under low pressures. This study provides a reference for fluorinated polymers as promising candidates for the insulation systems for all-electric aircraft.

Research on Flashover Voltage Prediction of Catenary Insulator Based on CaSO4 Pollution with Different Mass Fraction

Pollution flashover accidents occur frequently in railway OCS in saline-alkali areas. To accurately predict the pollution flashover voltage of insulators, a pollution flashover warning should be made in advance. According to the operating environment of insulators along the Qinghai-Tibet railway, the pollution flashover experiments were designed for the cantilever composite insulator FQBG-25/12. Through the experiments, the flashover voltage under the influence of soluble contaminant density (SCD) of different pollution components, non-soluble deposit density (NSDD), temperature (T), and atmospheric pressure (P) was obtained. On this basis, the GA-BP neural network prediction model was established. P, SCD, NSDD, CaSO4 mass fraction (w(CaSO4)), and T were taken as input parameters, 50% flashover voltage (U50%) of the insulator was taken as output parameters. The results showed that the prediction deviation was less than 10%, which meets the basic engineering requirements. The results could not only provide early warning for the anti-pollution flashover work of the railway power supply department, but also be used as an auxiliary contrast to verify the accuracy of the results of the experiments, and provide a theoretical basis for the classification of pollution levels in different regions.

Pollution Flashover Voltage of Transmission Line Insulators: Systematic Review of Experimental Works

Over the past decades, extensive experimental-based research works have been carried out to investigate the flashover phenomenon on the performance of polluted transmission line insulators. The critical focus has been on developing methods that can determine the safety, reliability, and sustainability of the overall power transmission network based on experimental results obtained from polluted insulators’ flashover voltage tests. In this paper, a systematic review of available scientific works, published as early as the 1990s, for the analysis of pollution flashover voltage, is undertaken. The review mainly focuses on factors influencing the efficiency of transmission line insulators under polluted conditions. Specifically, publication databases utilizing various synonyms and keywords associated with the terms “contaminated insulators” and “flashover voltage test” have been scrutinized. The search has resulted in 1364 articles, from which 97 articles have satisfied the review requirements and have been subsequently analyzed to determine the parameters associated with polluted insulators. Major factors that affect the performance of insulators, including electrical and environmental impacts, are discussed. Variations in factors affecting flashover test development and insulator efficiency are also considered. Overall, the current analysis provides an important insight toward successful evaluations of the health of transmission line insulators and research advancements of electric power transmission line insulators.

Online Condition Monitoring of Overhead Insulators Using Pattern Recognition Algorithm

In this paper commonly-used overhead line insulators are experimentally studied to propose an intelligent diagnosis system (IDS) to correctly identify the insulator health condition in real-time. The proposed IDS is developed based on three diagnostic indicators, third to fifth harmonic ratio of the insulator’s leakage current (LC), cosine of the phase angle of the LC fundamental component, and the ratio of the maximum electric field stress to flashover electric field of the insulator. The proposed diagnostic approach can identify the normal, abnormal and critical conditions of an insulator based on the above-mentioned indicators. Leakage current and flashover voltage are experimentally measured for the studied insulators under various health conditions. Then, recorded data are analyzed to calculate the proposed indicators corresponding to each insulator state. Measured and calculated data are used to intelligently quantify threshold limits of each indicator based on visualization algorithm. In this algorithm, different classifiers are trained with experimental data. The decision tree, which provided the highest precision, is employed to determine reference boundaries of the three indicators for each health state of the insulator. Embedded sensors can measure and sample the LC and electric field stress of the insulator. Sampled data are transmitted to a central processing unit-based receiver via a radio communication channel to automate the identification of the insulator state in real-time.

Influence of Conducting Particle on DC Flashover Characteristics and Tracking Property of GIS/GIL Insulator

Flashover at gas/insulator interface acts as a vital challenge to the safe and stable operation of gas-insulated system especially when involved with surface metallic particle. In this paper, flashover characteristics at SF₆/epoxy insulator interface were investigated concerning on the tracking property based on image analysis. DC flashover experiments were operated for basin-type spacer with metallic particle at various locations. Flashover voltage was obtained and tracking on the surface after successive flashover was captured. Improved image analysis method based on fractal theory was carried out to evaluate tracking pattern quantitatively. The relation between the fractal dimension of tracking and field distribution at particle tip was revealed. Obtained results showed that flashover voltage decreased due to severe field distortion with moving particle from ground to HV electrode. Meanwhile, fractal dimension of tracking covering the area from particle to ground electrode indicated centralized tendency. Simulation result confirmed this variation as the consequence of centralized field distribution at the tip of particle. The quantitative relation between fractal dimension and field distribution suggests new sight to estimate the influence of metallic particle on insulation property in the gas-insulated system.

Performance Evaluation of Outdoor High Voltage Glass Insulators in High Pollution Industrial Areas Using Simulated Acid Rain Contamination

A suitable, non-standard method for artificial pollution testing using simulated acid rain pollution in a laboratory was developed in this work. The method is applicable to a wide range of climatic conditions and rain acidities. The established method adopts the solid layer principle in the preparation and application of acid rain of various pollution severities to test insulators. Glass cap and pin insulators were contaminated, assembled into strings of two discs and flashover tests carried out on the strings at different orientation angles. The frequency of flashover occurrence, maximum withstand degree of pollution, effect of pollution severity, and effect of orientation angle were investigated. Test results showed that the orientation angle plays little or no role in the flashover of the insulators under dry conditions. Under wet conditions, the insulators performed better when inclined. Flashover voltage was observed to be inversely proportional to time while the time to flashover was inversely proportional to the pollution severity. The probability of flashover increases with an increase in voltage for a fixed pollution severity or increase in pollution severity for a fixed voltage level. This indicates that the probability of flashover is a function of the product of pollution severity and voltage.

Influence of Shed Shape on Direct-Current Pollution Flashover Voltage and Pressure Decrease Exponent

This study investigated the influencing mechanisms of shed shape on direct-current pollution flashover voltage and pressure decrease exponent through artificial pollution tests on a glass experimental model in Beijing (50 m altitude) and Tibet (4300 m altitude). Arc development prior to the flashover was quantitatively recorded using a high-speed camera, and three arc development modes along the pollution surface or in the inter-shed space were then extracted through arc development analysis. The occurrence probabilities of the three arc modes under various shed overhangs, altitudes, and shed spacings were analyzed. Mode probability was used to interpret the decreasing flashover voltage gradient with increasing shed overhang and decreasing shed spacing. Research indicates that pressure decrease exponent rises with shed overhang increase, as explained from the perspective of arc development probability. The quantitative relation between leakage distance efficiency and pressure decrease exponent was theoretically derived and its validity was proven through comparing the calculated with the measured.

Influence of Sheath Radial Crack on Flashover Arc and Leakage Current of Roof Silicon Rubber Insulator for High-Speed Train

In this paper, three types of insulators with no crack, short crack, and long crack are taken as the research objects to evaluate the influence of the penetrating cracks on the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> sheath of the roof silicone rubber composite insulator of high-speed train on the flashover characteristics. The continuous voltage rising method is used to obtain the influence characteristics of the crack on the development process of the flashover arc. The constant voltage withstand method is adopted to compare the leakage current when the contamination degree is 0.1 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The test results demonstrate that the crack has no significant effect on the flashover voltage and flashover path, and the flashover arc can burn the edge of the crack. The peak leakage current of the three different tests ranges from 24 mA to 30 mA. Additionally, the development of leakage current can be divided into four stages: rising, continuous violence, falling, and oscillating. Moreover, the sequence of the apparent leakage current of the insulator is long crack insulator, short crack insulator, and the one with no crack. The acceleration of the rising stage of the leakage current increases with the increase in the crack length. Meanwhile, the sum of the time of the rising stage, continuous stage, and falling stage of the insulator with long crack is the smallest. The crack will distort the distribution of current density and the electric field intensity in the vicinity. The results can provide references for evaluating the influence of radial cracks at the edge of the sheath on the flashover characteristics and optimizing the design of the roof insulator sheath structure.

Study on surface conductivity distribution of pollution layer during the propagation of local arc on the wet polluted insulation surface

The surface conductivity of the pollution layer plays a pivotal role in the investigation of flashover voltage and the propagating mechanism of the local arc. In order to study the characteristics of the pollution layer, an experimental system is designed in this paper. Ferric chloride is employed as the color indicator for demonstrating the dry state distribution of the pollution layer. Thus, the surface conductivity is calculated by analyzing the red–green–blue value of the pollution layer. In addition, a numerical model for calculating the heat transfer on the surface of the pollution layer is also established. It has been revealed that the dry state distribution of the pollution layer is affected by the leakage current and the speed of the local arc. Moreover, the relationship between the surface conductivity of the pollution layer and the thickness of the surface water film is obtained. The comparative analysis shows that the calculated results are in good agreement with the experimental data.

Self-diagnosis and High-flashover-strength Electroluminescence Coatings

In high-voltage power equipment, insulation defects are probably generated during the production, assembly, and operation processes, which degrade the insulation materials and even cause failure under electrical stresses. As a result, various detection and diagnosis methods for insulation status have been developed to discover potential defects in equipment, but extra testing devices are usually required. Insulation materials with special stimulus&#x2013;response performance, as an example, luminescence under the stimulation of intensified electric field or temperature induced by insulation defects, can be developed to realize self-detection and diagnosis of these defects. In this article, a self-diagnosis composite coating was prepared by filling electroluminescence zinc sulfide (ZnS) fillers into polydimethylsiloxane (PDMS). Two kinds of typical electrode configurations, namely, rod plane and needle plane, were processed to examine the luminescence characteristics of composite coating. The influence of the composite coating on flashover characteristics was also investigated. Experimental results indicated that ZnS composite coating exhibits obvious luminescence under relatively low voltage, and its luminance increases with electric field and ZnS content, which can effectively realize the self-detection and diagnosis function. Moreover, the composite coating can effectively improve the ac/dc surface flashover voltage. The approach presented herein provides a new insight for self-diagnosis of defects in power equipment.