Flashover Voltage Of Insulators Research Articles

Enhancement of DC Flashover Voltage of Epoxy Insulators and Gap Breakdown Voltage in SF6 Gas by Direct Fluorination of Metal Electrodes

Enhancement of DC Flashover Voltage of Epoxy Insulators and Gap Breakdown Voltage in SF₆ Gas by Direct Fluorination of Metal Electrodes

Statistical Analysis of Flashover Voltage of Solid Insulators Immersed in Insulating Oils and Quantification of the Ionization Rate Under LI Stress

Statistical Analysis of Flashover Voltage of Solid Insulators Immersed in Insulating Oils and Quantification of the Ionization Rate Under LI Stress

Surface Flashover Over a Microprofiled Cylinder in Air

Increasing the lightning impulse (LI) flashover voltage of insulators can require significant changes to the geometry and material properties of the insulator or electrodes. In some cases, such changes can be difficult to implement as they may require more volume or may compromise e.g. mechanical properties of the insulating parts. In this work, a new micro-scale surface profile which inhibits streamer discharge propagation without introducing major changes to the insulation system geometry or materials is demonstrated. Polyoxymethylene (POM) cylinders with 25 % glass fibre in air were machined with 0.5x0.4 mm rectangular grooves spaced 0.6 mm apart and stressed with LIs. A non-profiled cylinder and a cylinder with a larger, semi-circular grooves were tested for comparison. The cylinders were tested in a 48.5 mm atmospheric air gap with an exposed triple junction as the positive electrode. The rectangular surface profiles increased the LI flashover voltage (U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> %) from 70.0 to 96.5 kV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">peak</sub> . High-speed imaging showed positive surface streamer discharges stopping on the surface profiles. Discharge inception calculations were used to explain the influence of the surface profile on the flashover process. The results are relevant for technological applications with electrically stressed solid insulators in gases.

A critical study on detection of pollution level of overhead insulators by measuring pH and conductivity of the contaminants

The flow of electric power requires overhead insulators to maintain a safe distance between charged conductors and supporting structures. These insulators are installed in outdoor locations and are hence subjected to a variety of adverse environmental conditions, such as airborne dust and other contaminants. In moist conditions, these pollution factors can cause flashover, resulting in the loss of energy in the form of heat and light. Therefore, it is crucial to determine various types of contaminants based on geographical conditions and analyze their effects on the insulation capabilities of these insulators. This research work analyzes the accumulation of certain contaminants on the insulators installed at various geographical locations. Experimental approaches for detecting the level of contamination of insulators have also been examined, along with their limitations. Moreover, the findings of pollution tests performed in industrial, coastal, desert, inland, agricultural, and biological areas are presented as well. The flash-over voltage (FOV) of disc insulators made of porcelain for various pH and conductivity values has been observed to correlate FOV with pH and conductivity values of the pollutants. The pH and conductivity of contaminants are crucial factors impacting the insulator's flashover voltage, which is influenced by surrounding atmospheric conditions. Understanding the composition and monitoring these parameters can aid in developing preventive maintenance programs based on specified pH values, ensuring the reliability and performance of overhead insulators.

Effect of voltage waveshape and pressure on streamer breakdown criterion for predicting flashover voltage of polymeric insulators

The flashover voltage (FOV) of an outdoor insulator varies with atmospheric conditions and the voltage waveshapes. When altitude increases, the FOV decreases due to various atmospheric factors, mainly the pressure. The FOV of the insulator changes under normal operating conditions and transient over-voltages. As the flashover is dominated by streamer mechanisms, this study addresses the application of the streamer breakdown criterion to predict the FOV under different waveshapes and pressures. The Streamer breakdown criterion requires three parameters: electric field distribution, the relation between electric field and effective ionization co-efficient and the appropriate streamer initiation constant (K). The electric field distribution is computed using a FEM based electrostatic solver and the corresponding effective ionization coefficient is calculated. Though the computational procedures of the first two parameters are well defined, uncertainty exist in the value of K, as K depends on the type of gas, electrode geometry, gap distance, pressure, voltage waveshapes, etc. Though many studies have been carried out on configurations under AC, DC and LI only with different ranges of K, reports on the effect of voltage waveshape on the same configuration at different pressures are lacking. Hence, FOVs of an 11 kV polymeric insulator under DC, AC, LI, SI and the steepest VFTO for various pressures (0.75–1.013 bar) are measured and exact Ks are extracted. The necessity of the voltage waveshape-specific K range is inferred and quantified for accurate prediction of FOVs and also inferring the possibility of prediction of FOV without doing any experiments. The applicability of the K range for different arc lengths is verified using SiR samples.

Switching Impulse Flashover Performance of Nonuniform Pollution Insulators in Natural Environment

Under natural conditions, insulators show a nonuniform pollution state, which has a great influence on the switching impulse flashover voltage of insulators. Meanwhile, the insulation level of transmission lines is selected according to the switching impulse flashover voltage of nonuniform pollution insulators. For this purpose, in this article, the wet pollution method is used to simulate nonuniform pollution conditions. Then, the switching impulse flashover tests and the switching impulse flashover tests with preloading ac voltage are conducted on two types of insulators, XP-70 and LXY-70, in natural environment. The flashover voltage of insulators is obtained, flashover performances are analyzed, and the flashover processes of insulators are photographed. Moreover, the equations of flashover voltage gradient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{{50}}$ </tex-math></inline-formula> under nonuniform pollution conditions are established. The results indicate that there is a conspicuous polarity effect and a polarity reversal phenomenon under different conditions. Besides, as the increase of the ratio of bottom surface pollution to top surface pollution, the flashover voltage changes in the opposite case of preloading and non-preloading ac voltage. Finally, the switching impulse flashover voltage of ordinary porcelain and glass suspension insulators under nonuniform pollution conditions can be calculated based on the established equations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{{50}}$ </tex-math></inline-formula> . The results can provide theoretical support for the reasonable selection of the insulation level of transmission lines, which in turn can greatly reduce the cost of the transmission lines.

A Dynamic Intelligent Approach Based on Gaussian Function for Prediction of the Flashover Voltage Conditions on Polluted Polymer Insulators

This research presents a dynamic modeling approach to predict flashover voltage (FOV) of polymer 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 study, experimental results of pollution flashover tests are used to develop a circuit model of pollution arcs based on Obenaus’ model. Estimation of circuit values is done by use of intelligent algorithm with no dependency on profile of insulators which is also more beneficial than typical analytical calculations. Then, separation and investigation of discharge and pollution voltage is done and proper classification is made. This classification is later used to predict pre-flashover conditions and pollution flashover. Gaussian model is used to make fitness of voltage of pollution layer and voltage of discharge on the surface of insulator. Gaussian representation of each stage in pollution flashover contains critical signals leading to complete discharge. Based on the obtained model, a flowchart is presented to predict dynamic stages of flashover. Comparison to various experimental data shows close correlations with the results of proposed model. An online monitoring system can be developed according to obtained results in order to prevent pollution flashover.

Impact of volcanic ash from Cotopaxi-2015 and Tungurahua-2016 eruptions on the dielectric characteristics of suspension insulators, Ecuador

In Ecuador, a country with several active volcanoes and with four eruptions in the last decade in the continental arc, it is very likely that high-voltage transmission lines cross volcanic hazard zones on their routes. Here, we quantify the impact of fresh volcanic ash from the hydromagmatic Cotopaxi-2015 and the magmatic Tungurahua-2016 eruptions on the dielectric characteristics of ANSI 52–3 suspension insulators made of porcelain and glass, under moist conditions. The experiments include two methodologies to measure the performance of the insulators in real-time: the minimum insulator flashover voltage (FOVmin) and the dielectric loss factor angle. Both allow quantifying i) the critical voltage that the insulators can withstand prior to flashover occurrence and, ii) the strong fluctuating behavior that the insulators undergo in an ashy environment. Based on six contamination scenarios, we found that there is a higher chance of flashover if the insulators are completely blanketed (top and bottom) even with a fine ash layer (1 mm), than if they are covered just at the top. Our results further show that the ash of Cotopaxi-2015 eruption has a higher chance of leading to insulator failure because of its higher conductivity (i.e. higher leachate content) than that of Tungurahua-2016. Additionally, we identify two critical voltages prior to electrical flashover on the insulators of 28.25 kV and 17.01 kV for the 230 kV and 138 kV Ecuadorian transmission lines, respectively. Finally, we present a simple impact evaluation for the main Ecuadorian transmission lines based on the outcomes of this research and the official volcanic hazard maps for Cotopaxi and Tungurahua volcanoes.

Surface Flashover Induced by Metal Contaminants Adhered to Tri-Post Epoxy Insulators under Superimposed Direct and Lightning Impulse Voltages

Metal contaminants can distort the surface electric field of the tri-post epoxy insulator and cause serious surface charge accumulation, significantly reducing the insulation performance of the insulator under the superimposed DC and lightning impulse voltage. In this paper, an experimental platform for charge accumulation and surface flashover of tri-post epoxy insulators under the superimposed DC and lightning impulse voltage was built, by surface point measurement and charge inversion calculation, the surface charge distribution characteristics of tri-post insulators with attached particles was experimentally explored and the influence law of attached metal particles on the charge accumulation was discussed. The results show that metal particles can cause a surge in the surface charge density of the tri-post epoxy insulator, forming bipolar charge spots whose polarity is opposite to that of the adjacent electrodes. The adsorbed metal dust can cause the polarity reversal of adjacent surface charges, forming a large-area unipolar charge spot. Moreover, the flashover voltage of a tri-post insulator under DC superimposed lightning impulse voltage with a clean surface and attached metal particle was measured, and the synergistic induction mechanism of charge spot accumulation and metal particle discharge on the flashover along the face of the tri-post insulator is thereby revealed. Compared with the clean insulators, the surface flashover voltages of tri-post epoxy insulators with metal contaminants adhered decrease under the superimposed voltages of different polarities, but the decline amplitude is greater under the heteropolar composite voltage. When adhered to the middle of the insulator leg, the distribution range of bipolar charge spots is the widest, and the surface flashover voltage decreases sharply, which can drop by 32% compared with the absence of particles. In addition, when the metal dust adsorbed by the tri-post epoxy insulator has a wide distribution range, the impact of metal dust on the flashover voltage is greater than that of the attached metal particles, and its hazard cannot be ignored. The research results can provide a reference for the insulation test method and optimal design of the DC tri-post epoxy insulator.

Flashover Voltage of Epoxy FRP Insulators with Different Surface Roughness and Groove under Nanosecond Pulses in SF6

In order to further improve the insulation performance of fiber reinforce plastic (FRP) materials used in electromagnetic pulse (EMP) simulators, the flashover characteristics of FRP materials with different surface roughness and groove, i.e., those who are easily achieved and have a prominent effect, are investigated in 0.1 MPa SF6 under nanosecond pulse voltage with a rise time of 20–30 ns. The experimental results show that surfaces with different roughness have no significant influence on the flashover voltages of the FRP insulators, and both the convex grooves made of FRP and the convex grooves with nylon rings inlaid to form projections can improve the surface flashover voltage of epoxy FRP insulators under nanosecond pulse, in which the effect of the former surface is more obvious. For the insulators with convex grooves made of FRP, it is found that the root of the FRP protrusions breaks down after a number of shots with the occurrence of carbonization channels and spots, which is nonexistent for the nylon projections. Combined with the test results of surface characteristics, the surface roughness and the secondary electron emission yield (SEEY) are not key factors of flashover characteristics in SF6 under nanosecond pulse, arguably due to the fact that the energy needed for an incident electron to ionize an SF6 molecule is lower than that to excite two secondary electrons. Hence, the flashover performance cannot be improved by adjusting the surface roughness, and the flashover channel is principally governed by the macroscopic distribution of electrical field which can be changed by the convex groove. Breakdown phenomena of FRP protrusions indicate that the bulk insulation performance of resin FRP is weaker compared to pure resin because of its composite structure, as well as the impurities and voids introduced in the manufacturing process. The results are instructive for the design of FRP insulation structures in the compact EMP simulator.

Classifying insulator conditions of room temperature vulcanized coated glass insulators under different coating damage modes

The damage of the room temperature vulcanized (RTV) coating on the surface of polluted glass insulators under axial and circumferential directions has a significant influence on the insulator's leakage current and flashover voltage. To date, many investigations have been conducted on the performance of polluted glass insulators under longitudinal, ring-shaped, and fan-shaped coating damage modes. The purpose of this research was to investigate and classify the insulator conditions of RTV coated glass insulators under different coating damage modes using flashover voltage magnitude and leakage current characteristics. The harmonic component index of leakage current used to determine the health status (H) of insulators, and the crest factor (CF) of leakage current, were experimentally extracted and utilized in the classification. The support vector machine (SVM) model with various functions was designed to predict the deterioration configuration of RTV coatings on polluted glass insulators. The results indicate that the flashover voltage and leakage current of polluted glass insulators are significantly affected by different coating damage modes. Specifically, the insulator with the fan-shaped RTV coating damage experiences the most vulnerable pollution effect compared to the undamaged coating, with a 48% drop in the flashover voltage and a 125% increase in the leakage current under heavy pollution. Subsequently, the proposed SVM model demonstrates strong capabilities for predicting the flashover voltage and leakage current and classifying the pollution severity of the RTV coating damage based on the extracted indicators.

Study on the relationship between the characteristics of water droplets on the shed of composite insulators and the pollution flashover voltage

The anti-pollution flashover characteristic of composite insulators is the main indicators to evaluate their electrical performance, and the pollution flashover voltage can directly characterize the anti-pollution flashover characteristics of the insulators. This paper proposed an on-line detection method for the pollution flashover voltage of composite insulators. Samples of composite insulator shed with different hydrophobicity were prepared by using NaOH solution with pH value of 13 and temperature of 80 °C. According to the distribution of water droplets on the surface of the sample, the characteristic parameter of the number of water droplets was proposed. The samples with different characteristic parameters were smear-stained and used for the pollution flashover voltage test. The relationships between the number of water droplets on the sample surface and the pollution flashover voltage and leakage current were obtained, which can provide guidance for the evaluation of the operation state of composite insulators.

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.

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.

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.

Electric Field Distribution and AC Breakdown Characteristics of Polluted Novel Lightning Protection Insulator under Icing Conditions

As a result of lightning strikes, pollution, and ice, overhead distribution wires might be short-circuited and trip. As a result, researchers have developed a new lightning protection composite insulator. There is still a need to test its pollution and icing performance. Based on the finite element and field test method, this paper studies the electric field distribution and AC (Alternating Current) breakdown characteristics of polluted novel lightning protection insulators under icing conditions. Firstly, the finite element calculated results show that this novel insulator’s electric field distribution is different from that of a conventional insulator. The locations with sizeable electric fields are located in the insulation section, and the electric field in the arrester section is tiny. In addition, when the insulator surface is covered with ice, there is an increase in the electric field along the surface and pin electrodes. Compared with the dry conditions, when there is an ice layer and icicle, electric field peaks increase by 48.85% and 46.08%, respectively. Secondly, the test results show that there are three types of arc paths in different pollution levels. The arc paths are related to ESDD (equivalent salt deposit density) under icing conditions. Uf shows a downward trend with increased pollution levels, and the maximum flashover voltage is 2.70 times more than the minimum. Finally, four fitting methods are proposed in this paper. After comparing the goodness of fit of different functions, the quadratic function and negative power function with the constant term are recommended as empirical formulas for calculating flashover voltage of novel insulators under icing conditions in different pollution levels. The research results of this paper have a specific guiding role for the selection of the external insulation of transmission lines and structural optimization of novel insulators.

Dynamic behaviors and self-cleaning property of droplet on superhydrophobic coating in uniform DC electric field

The application of the superhydrophobic coating is expected to be an effective method to further improve the pollution flashover voltage of insulators. However, so far, the relationship between electric field strength, droplet volume, and sliding angle in strong electric fields is not clear. This is not conducive to the evaluation of the practical application effect of superhydrophobic insulators. In this paper, the self-cleaning property of superhydrophobic coating and the critical motion condition of droplets in the electric field were analyzed theoretically. Then an experimental platform was set up to observe the movement of the droplet driven by the electric field, and the critical electric field strength for droplet motion was measured. Experimental and theoretical analysis results show that the critical electric field strength for positive droplet motion is less than that for the negative droplet. The droplet driven by the electric field can also remove water-insoluble pollution particles. And the maximum pollution concentration that droplets can remove by means of self-cleaning performance is calculated theoretically. The theoretical calculation method of the sliding angle of superhydrophobic coating in uniform DC electric field is obtained, which is in good agreement with the experimental results. This paper provides theoretical support for evaluating the practical performance of the superhydrophobic insulator in strong electric fields.

AC flashover characteristics and arc development process of glaze ice-covered insulators in natural environment

Ice accretion on the insulators can reduces the creepage distance to a certain extent as low as the dry arc distance, which may cause flashover trip and subsequent blackout. Extensive research on insulator icing has been carried out in a controlled-climate room. Due to great differences in environmental parameters between laboratory simulation and field tests, icing characteristics and discharge development of ice-covered insulator obtained in the laboratory cannot veritably reflect natural icing law and arc propagation process. Consequently, in the present study the glaze-icing on energized insulators was investigated on site, and the mechanism of icicle growth on the insulator energized with different voltage levels was revealed. Meanwhile, AC flashover performances and arc discharge development of ice-coated insulators for the two test conditions were compared and discussed. Results show that for a weak electric field, icicle firstly grows vertically, and then bends to the axis of the insulator when its length reaches to a certain level. Nevertheless, icicle develops towards the axis at the beginning under a high electric field. AC flashover voltage of ice-accreted insulators increases exponentially with an increasing applied voltage, while the relation of flashover voltage and ice weight fits well with a negative power function. Icing flashover voltage of the insulators obtained in natural environment is 14%～21% higher than that in the chamber. Compared with the flashover in the laboratory, during the discharge of the insulators naturally covered with ice, arc extinction-reignition and floating phenomena are more significant, and the ice-melting is more severe.

Statistical analysis on the DC discharge path of ice-covered insulators under natural conditions

Ice flashover of insulators seriously affects the safe operation of transmission lines. Flashover path of ice-covered insulators is one of the key influence factors. Due to the randomness and complexity, the existing researches lack the systematic and in-depth study on the flashover path of ice-covered insulators. In this paper, a large number of flashover tests of ice-covered insulators are carried out in the natural field. The flashover paths are classified by its characteristics as transverse bridging arc and longitudinal bridging arc, which are analyzed by probability statistics. The effects of icing degree and string length on various types of arc are analyzed. In addition, the leakage distance utilization ratio is defined to analyze the influence of flashover path on flashover voltage. The results show that as the icing degree becomes heavier, the probability of longitudinal bridging arc gradually increases, while transverse bridging arc gradually decreases. The influence of string length on arc type is related to the icing degree. Under mild icing condition, the probability of longitudinal bridging arc and transverse bridging arc has nothing to do with string length, but under moderate icing condition, with the increase of string length, the probability of transverse bridging arc increases significantly. Moreover, it is also found that the effect of flashover path on the leakage distance utilization ratio is one of the reasons that leads to the non-linearity of flashover voltage of long ice-covered insulators.

Prediction of the Optimal Umbrella Shape of Insulators Based on Data Mining Technology

The insulator flashover process is affected by many factors. In order to better study the factors that affect the insulator flashover voltage, and then accurately predict the insulator flashover voltage. In this paper, 11 different types of composite insulators are studied through artificial pollution tests. Data mining technology has been widely used now. In order to better apply data mining in the prediction of insulation flashover voltage, this paper adopts the BP neural network in data mining technology to predict the flashover voltage of different umbrella-shaped insulators. In addition, in order to further improve the prediction accuracy of the model, this paper uses the global search capability of genetic algorithm to optimize the initial weights and thresholds of the BP neural network, and optimizes the BP neural network prediction model, and established an optimization model based on genetic algorithm to optimize BP neural network. Through this method, the flashover voltage of the insulator can be predicted in time, which is of great significance for maintaining the safe and stable operation of the power system.