Flashover Voltage Of Insulators Research Articles

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.

Prediction of Insulator Pollution Flashover Voltage Based on Data Mining Technology

The pollution flashover of insulators is of great significance to the safe and stable operation of power grids. Therefore, studying the pollution flashover voltage of insulators has very important guiding value for the external insulation prevention of power grids. For this reason, this article has obtained the flashover voltage under different salt densities and gray densities through manual pollution tests. Data mining technology is now widely used. In order to better apply data mining to the insulation flashover voltage prediction,this paper adopts the support vector machine regression method in data mining technology to establish a prediction model to predict the insulator pollution flashover voltage. 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.

A Novel Method for Visualizing the Pollution Distribution of Insulators

Knowing more about insulator pollution is of guiding significance to the development of anti-pollution strategies. Traditional methods can be used to determine only the pollution degree of insulators. However, the pollution distribution also has a substantial influence on the flashover voltage of insulators even under the same equivalent salt deposit densities (ESDD). In this article, an ESDD spectral density method and a visualization method based on hyperspectral technology are proposed. The proposed method presents the ESDD distribution using hyperspectral images. A detection model based on characteristic wavelengths is established with partial least squares regression to detect the insulator ESDDs. Based on the ESDD detection results, the features of the ESDD spectral density process, including the building of the ESDD probability graph, the overall ESDD, and visualization of the ESDD, are presented. Example analyses of field-operating insulators were conducted, revealing that the ESDD spectral density can be used to track the pollution distribution of insulators and that the pollution degree can be calculated from the overall ESDD. The error of the overall ESDD calculated by this method is within 10%. In addition, visualization of the pollution distribution can more intuitively record the degree of pollution and the nonuniform distribution characteristics. Both the pollution degree and distribution can be obtained by this method. Therefore, hyperspectral technology can overcome the limitations of traditional methods and convert the ESDD results into an image to determine the ESDD distribution. These research results provide theoretical instruction for guiding insulation design and anti-pollution strategies for operating transmission lines.

Prediction of Critical Flashover Voltage of High Voltage Insulators Leveraging Bootstrap Neural Network

Understanding the flashover performance of the outdoor high voltage insulator has been in the interest of many researchers recently. Various studies have been performed to investigate the critical flashover voltage of outdoor high voltage insulators analytically and in the laboratory. However, laboratory experiments are expensive and time-consuming. On the other hand, mathematical models are based on certain assumptions which compromise on the accuracy of results. This paper presents an intelligent system based on Artificial Neural Networks (ANN) to predict the critical flashover voltage of High-Temperature Vulcanized (HTV) silicone rubber in polluted and humid conditions. Various types of learning algorithms are used, such as Gradient Descent (GD), Levenberg-Marquardt (LM), Conjugate Gradient (CG), Quasi-Newton (QN), Resilient Backpropagation (RBP), and Bayesian Regularization Backpropagation (BRBP) to train the ANN. The number of neurons in the hidden layers along with the learning rate was varied to understand the effect of these parameters on the performance of ANN. The proposed ANN was trained using experimental data obtained from extensive experimentation in the laboratory under controlled environmental conditions. The proposed model demonstrates promising results and can be used to monitor outdoor high voltage insulators. It was observed from obtained results that changing of the number of neurons, learning rates, and learning algorithms of ANN significantly change the performance of the proposed algorithm.

Temporal and spatial characteristics of soluble salt components accreted on the insulator surface

Due to the differences in typical pollution sources, the soluble salt composition deposited on the naturally contaminated insulators varies with the region. As different soluble salts have different effects on the pollution flashover voltage of insulators, it is necessary to investigate the spatial and temporal distribution of the soluble salt composition deposited on the insulator surface to make the external insulation design more scientifically and reasonably. In this study, an artificial contamination test platform was built to collect the contamination naturally deposited on the specimens. The test results showed that the contamination composition deposited on the specimen was similar to that in the atmosphere, and the inclination angle of the specimen and the duration of pollution deposition had little influence on the contamination composition. After examining the industrial post insulators from actual substations, it was found that the contamination composition was almost the same for different insulator surface materials, insulator shed types, and voltage polarities. It was also found that the deposited contamination was mostly influenced by pollution sources. The results can provide a reference for the studies of pollution distribution of natural insulators.

Forecasting Flashover Parameters of Polymeric Insulators under Contaminated Conditions Using the Machine Learning Technique

There is a vital need to understand the flashover process of polymeric insulators for safe and reliable power system operation. This paper provides a rigorous investigation of forecasting the flashover parameters of High Temperature Vulcanized (HTV) silicone rubber based on environmental and polluted conditions using machine learning. The modified solid layer method based on the IEC 60507 standard was utilised to prepare samples in the laboratory. The effect of various factors including Equivalent Salt Deposit Density (ESDD), Non-soluble Salt Deposit Density (NSDD), relative humidity and ambient temperature, were investigated on arc inception voltage, flashover voltage and surface resistance. The experimental results were utilised to engineer a machine learning based intelligent system for predicting the aforementioned flashover parameters. A number of machine learning algorithms such as Artificial Neural Network (ANN), Polynomial Support Vector Machine (PSVM), Gaussian SVM (GSVM), Decision Tree (DT) and Least-Squares Boosting Ensemble (LSBE) were explored in forecasting of the flashover parameters. The prediction accuracy of the model was validated with a number of error cost functions, such as Root Mean Squared Error (RMSE), Normalized RMSE (NRMSE), Mean Absolute Percentage Error (MAPE) and R. For improved prediction accuracy, bootstrapping was used to increase the sample space. The proposed PSVM technique demonstrated the best performance accuracy compared to other machine learning models. The presented machine learning model provides promising results and demonstrates highly accurate prediction of the arc inception voltage, flashover voltage and surface resistance of silicone rubber insulators in various contaminated and humid conditions.

Study on Surface Flashover Characteristics in SF6/CF4 Mixture

Surface flashover characteristic of epoxy resin composite material in SF6/CF4 mix gas were studied through experimental method, and the influence of several key parameters were analyzed, such as gas pressure, SF6 mix ratio and voltage polarity. It is shown that, when the mix ratio of SF6 in the mixed gas is 40%, the flashover voltage of epoxy resin insulator can reach over 60% of the flashover voltage in SF6 with the same pressure. The synergistic effects in the needle-plate electrodes system have significant difference between positive and negative polarity. The synergistic effect for negative polarity is weaker than that in negative polarity. Comprehensive environmental requirements and surface flashover characteristics, the results provide a potential SF6 alternative for GIS equipment.

Correction of flashover voltage of catenary insulators based on analysis of soluble salt compositions in saline‐alkali region

AbstractCalcium sulfate and other slightly soluble salts in the natural pollution of catenary insulators could result in differences in flashover voltages between artificially and naturally polluted insulators at the same salt deposition density. Based on the insulator pollution characteristics in saline‐alkali areas and the saturated water absorption of polluted insulators, the equivalent salt deposit density and nonsoluble deposit density of insulators are corrected according to the influence of other coexisting soluble salts on the solubility of calcium sulfate. The correction formula of the insulator flashover voltage is proposed, which considers the equivalent salt deposit density, nonsoluble deposit density and pollution components. The results from the correction formula are compared with the experimental data from the artificial pollution test of the ceramic cap and pin insulator. The results show that salt‐alkali areas are more easy to flashover than other areas. The remaining pollutants can change the conductivity of the pollutant layer by inhibiting or promoting the dissolution of calcium sulfate. Moreover, its effect on the flashover voltage cannot be ignored. The error between the calculated value based on the correction formula and the experimental data is below 6%. A pollution flashover warning mechanism based on relevant meteorological data is proposed. The results can be used as an important reference for the operation and maintenance of catenary insulators in saline‐alkali areas. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DC pollution flashover performance of HVDC composite insulator under different non-uniform pollution conditions

The non-uniform air flow field and electrical field distributing around insulators cause uneven deposition of pollution particles on different positions and parts of the insulator surfaces. Pollution-induced flashover is a serious threat to the safe operation of the power system, and non-uniform pollution distribution has great influence on flashover voltage of insulators. Towards this, in this study, the solid layer method was used to simulate different non-uniform pollution conditions. Then, DC pollution flashover tests of composite insulators were carried out and the flashover performances were analyzed. The results indicated that the increase of KL/W (from 1 to 15) decreased U50 by 27–32%. While the increase of KT/B (from 1 to 10) increased U50 by 35%, and the increase of KH/M (from 1 to 4) increased U50 by 25%. Where KL/W, KT/B and KH/M are the SDD (salt deposit density) ratio of windward to leeward side, top to bottom surface and high voltage to middle group respectively. Besides, higher proportion of leeward side area will reduce U50. U50 and SDD are still in agreement with the negative power function relationship, non-uniform pollution conditions have great effect on a (constant of power function), but less impact on n (characteristic index of power function). Finally, equations for calculating different non-uniform pollution flashover voltages were established and validated, also the relative errors are acceptable. The results are very important for guiding insulation design and anti-pollution works of operating transmission lines.

Pollution flashover performance of RTV coatings with partial damage

Under conditions of high temperature, high humidity, and strong ultraviolet radiation, RTV coating on the insulators may get aged, powdered and even peeled off. The physical damage of the RTV coating on the insulator surface can result in a reduction in the pollution flashover performance. Therefore, this study investigated the influence of location, lateral length, and longitudinal length of the damage on the pollution flashover voltage of RTV-coated insulators. From the experimental results, it was found that the longitudinal length of the damage along the creepage distance direction was the most influential factor on the pollution flashover voltage. According to the flashover voltage function obtained by fitting, the concept of “effective path” distance was proposed. This concept can be used to analyse the influence of multiple damages on the pollution flashover voltage. To validate the analysis, verification experiments were performed using typical industrial insulator. The results showed that the pollution flashover voltage of the insulator was also in a linear relationship with the proposed “effective path” distance, which confirmed the mechanism analysis.

Influence of humidity on conduction processes in gas‐insulated devices

Humidity has been considered as one of the main influencing factors that determine the conduction processes and electric strength of gas-insulated systems. Whereas in the past, various studies focused on the change in the partial discharge inception voltages, breakdown strength of homogeneous and inhomogeneous field arrangements, and insulator flashover voltage, recent studies have investigated the changes in ion currents measured through different gas gaps. In the framework of this contribution, a highly precise humidity control circuit has been developed to analyse the significance of humidity in the range from −25 to −5°C frost-point, which is fully applicable to operating gas-insulated devices. Using sulphur hexafluoride (SF6) as the insulation gas at 0.45 MPa, Al2O3-filled epoxy resin insulators, and technically rough electrodes, the humidity was found to significantly influence the intensity of microdischarges at interfaces. Charge generation from microdischarges at the interfaces substantially increased with increasing humidity. For an electric field of 5 kV/mm that were applicable to the dimensioning of gas-insulated devices, humidity strongly influences the charge provision from technically rough interfaces and potentially contributes to the surface-charge accumulation at insulator surfaces. On the other hand, for low-field conduction phenomena, no increase in the ion currents from natural ionisation or electrophoretic conduction was observed. For the investigated range of parameters, humidity is expected to be highly relevant for the design of gas-insulated devices.

AC Flashover Voltage Model for Polluted Suspension Insulators and an Experimental Investigation in Salt Fog

In recent years, the electrical performance of polluted suspension insulators operating in coastal foggy regions has attracted wide attention because of the occurrence of flashover. Surface wetting by salt fog accretion increases the surface conductivity and degrades the flashover voltage of insulators. Normally, the effect of conductivity under fog condition and pre-contamination on the flashover of polluted insulators are analyzed separately. Therefore, this does not reveal the flashover characteristic in salt fog, which requires further research. This paper describes salt fog experiments with an AC test voltage conducted using suspension insulators in a 110-kV power system. The electrical strength performance of insulators with salt fog treatments is analyzed, and the effects of salt deposit density (SDD) and the fog water conductivity (FWC) on the flashover of three types of suspension insulators are studied. The concept of additional SDD is proposed to quantify analyze the effects of salt fog. The results show that there is less dependence on FWC at higher pollution levels than at lower pollution levels. That is, the effect of FWC on 50% AC flashover voltage ($U_{50}$ ) can be neglected for SDD >0.15 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , whereas FWC has a strong effect on $U_{50}$ for SDD <; 0.15 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . FWC has a greater influence on $U_{50}$ of ceramic insulators than on that of silicone rubber insulator. A model for calculating the critical flashover voltage of insulators is proposed by considering the combined effect of FWC and pre-polluting SDD.

New experimental study on the DC flashover voltage of polymer insulators: combined effect of surface charges and air humidity

This research provides conclusions that can partially cover the lack of knowledge related to the effects of ambient atmospheric conditions on DC electric power transportation. Two polymer insulating materials are used for completing this research study. Inside a climate chamber, the relative humidity is controlled and adjusted from 20% to 80% RH. Then, the samples are charged with positive or negative charges by applying ± 20 kV to the corona-generating ring of needles. The surface potential is measured using an electrostatic voltmeter and is converted into surface charge density later by applying the probe response matrix method. The pre-charged samples are then stressed with high-voltage negative or positive DC values inside the climate chamber over a range of controlled values of the surrounding air humidity until flashover takes place. The space charges, which can drift in the air gap to reach the solid surface, are highly affected by the level of the relative humidity of the surrounding air. Also, increasing humidity results in a reduction of the DC flashover inception voltage and a shorter time to flashover regardless of the voltage polarity. Moreover, the positive or negative flashover inception voltage of both materials increases with pre-deposited negative charges while it decreases with pre-deposited positive charges.

Experimental and Estimation of Flashover Voltage of Outdoor High Voltage Insulators with Silica Filler Based on Grey Wolf Optimizer

Abstract Epoxy is used widely in high voltage outdoor insulator because of its light weight (this avoids the need to use heavy cranes for their handling and installation and this reduces cost), easy handling, easy blending with additives, and having hydrophobicity. This paper focuses on improving epoxy electrical characteristics (flashover voltage) for high voltage outdoor insulator by adding silica filler. Composite of epoxy with silica filler: silica is prepared with 0 %, 10 %, 20 %, 30 % and 40 % weight percentages concentration. The flashover voltage (FOV) is tested under various environmental conditions with different samples lengths. Grey wolf optimizer (GWO) is developed to predict the best optimal value of flashover voltage under various environmental conditions using laboratory measurements of flashover voltage. The obtained results from GWO are compared with experimental measured data. Results showed an improvement with silica concentration at different samples lengths in flashover voltage for composite samples over epoxy without any additions. A comparison between three different conditions showed higher flashover voltage for samples in dry condition than that of samples in (wet, salt wet) conditions.

3D printing fabrication of conductivity non-uniform insulator for surface flashover mitigation

Solid insulators applying functionally graded material (d-FGM) have spatially non-uniform dielectric properties. The d-FGM insulator is effective on insulation performance improvement without complicating the structure; however, the fabrication of such insulators remains a challenge. To investigate the feasibility of 3D printing technology on d-FGM, we designed and fabricated a conductivity non-uniform insulator and tested its surface flashover characteristics. First, a modified genetic algorithm is employed to design the conductivity distribution in the non-uniform insulator. The designed insulator is then fabricated using a 3D printing process named fused deposition modeling (FDM), in which we verified the applicability of 3D printing materials on electrical insulation. Finally, compared to the uniform insulator, the surface flashover voltages of non-uniform insulators were improved by 23% in SF6 and 20% in vacuum. From above, we envision potential application feasibility for 3D printing of d-FGM in practical insulation design.

Grading of electric field distribution of AC polymeric outdoor insulators using field grading material

In this work, composite materials with nonlinear conductivity are used to enable grading of the electric field distribution along polymeric outdoor insulators, particularly near the high-voltage and ground terminals. A ZnO spherical microvaristor/carbon fiber (CF)/ silicone rubber (SR) composite is used as the field grading material (FGM). Finite element method-based numerical simulations are performed to analyze the electric field distributions of 220 and 500 kV composite insulators when the nonlinear conductivity type composite material is used. The 220 and 500 kV composite insulators are fabricated based on the results of the simulations and optical electric field sensors are used to measure their electric field distributions under normal operating conditions. The electric field distribution along the composite insulators are shown to be improved through use of the FGM, and the simulation results are consistent with the experimental results. These graded electric field distributions may reduce the degradation of the polymer materials used in composite insulators and extend their lifetimes. In addition, the dry flashover voltages of insulators with FGMs are higher than those of traditional insulators.

A Low-Cost Evaluation and Correction Method for the Soluble Salt Components of the Insulator Contamination Layer

Presently, equivalent salt deposit density (ESDD) is widely used by scientists and utility engineers to describe the site pollution severity due to its simple measurement procedure. When the contaminants are naturally accumulated on the insulator surface, some slightly soluble salts are only partially dissolved under saturated moisture condition. However, due to the large water consumption in the ESDD measurement process, these slightly soluble salts can be totally dissolved. Therefore, the measured ESDD may be higher than the actual pollution severity on the insulator surface. Thus, if using the measured ESDD to evaluate the flashover voltage of insulators in artificial pollution tests, the obtained results may be different from that of naturally contaminated insulators. This paper studied the dissolution amounts of highly and slightly soluble salts in the contamination layer by the ESDD measurement and compared them with a method proposed in this paper. The proposed method measures the surface conductivity of insulator under actual saturated moisture condition and can be used to correct the soluble salt components of natural contamination. Based on this method, a simple and novel device were also developed. The method proposed and device developed in this paper will be particularly useful for the selection and the design of insulators used in transmission lines.