Solid Layer Method Research Articles

Development of Laboratory Test Method to Perform Artificial Pollution Test on Composite Insulators Intended for HVDC Applications by Solid Layer Method

Development of Laboratory Test Method to Perform Artificial Pollution Test on Composite Insulators Intended for HVDC Applications by Solid Layer Method

Experimental Analysis of Ceramic Insulators with Different Profiles Under Very High Pollution Zone by Solid Layer Method

The outdoor insulators in service are exposed to marine, agricultural waste and industrial pollution. These pollutants get deposited on the insulator surface and lead to flashovers under fog conditions. There has been an abnormal increase in pollution levels due to rapid industrialization in the past two decades. This exponential increase in pollution levels causes frequent flashovers of insulators, leading to the tripping of transmission lines consecutively may result in blackouts, which severely affects the reliability of the power systems. The ESDD and NSDD measurement on the insulator surface are critical parameters for determining the pollution severity levels. This paper discusses ESDD and NSDD measurement procedures. In this paper, field pollution severity has been simulated in the Artificial Pollution Lab. In addition, the Non-Soluble Deposit Density (NSDD) component of pollutants for designing the creepage distance of ceramic insulators under heavy pollution conditions has been emphasized.

Characterization and Analysis of Intelligent Eco-Friendly Coating for Porcelain Insulator Flash-Over Protection

Among all the astonishing equipment found in power transmission and distribution networks, the insulator plays a vital role by providing mechanical support and electrical protection to power system. Despite all these noteworthy facts, the breakdown of insulators owing to surface contaminants appears to be particularly fascinating in today’s scientific world. Researchers provide a plethora of methods to eradicate this problem. Amidst the methods, superhydrophobic coating for insulators which is one of the widely used method, provide better solution as it offers resistance to moisture, wetness, dust and ice. This unique property of superhydrophobic coated insulators require further investigation. Hence to achieve this purpose, preparation of eco-friendly superhydrophobic solution of PDMS (Poly di methyl siloxane) with MTMS (Methyl tri methoxy silane) composites was made and analysed. In this study superhydrophobic coatings were prepared by using sol-gel method and spray coating technique. Authors performed characterization studies by using goniometer to measure the contact angle (CA) for superhydrophobic coating on insulator surface and it was found to be from 165° to 170° and sliding angle was from 5° to 10° confirming superhydrophobic property. Fourier Transforms Infrared Spectroscopy (FTIR) analysis validates the chemical composite of the coatings. Scanning Electron Microscope (SEM) analysis was used to observe the surface morphology of coating with estimated thickness L = 2 μm.Thermogravimetric analysis (TGA) was conducted to study about thermal withstanding limit of the coating above 600 °C. Finally, in an intentional contaminated conditions based on solid layer method of IEC60507 standards and IEC 60587 standards insulation resistances were tested using a megger instrument and self-cleaning ability of coating was also determined in this research.

Pollution Flashover Under Different Contamination Profiles on High Voltage Insulator: Numerical and Experiment Investigation

This work aimed to study the influence of contamination profiles and humidity on flashover electrical characteristics of polluted insulators. Firstly, the flashover tests on cap and pin glass insulators under four pollution levels represented by salinity were conducted. Eight artificial contamination profiles based on the solid layer method have been modeled for the selected insulators. The numerical analysis has been used to determine the insulator electrical characteristics such as potential, electric field, and power dissipation under proposed contamination profiles using finite element methods (FEM). Next, the power dissipation has been simulated with consideration of thermal stress propagation in locations with high power. Finally, flashover voltage gradient tests have been conducted under various humidity and contamination profiles. The values of the flashover voltage gradient due to pollution were determined as the percentage of the value of the flashover voltage gradient in the clean condition which was identified as the reference point. The numerical model indicated that the initiation of arc generally occurs at area in which the electric field and power dissipation is maximum. It was also observed from experimental results that the flashover voltage gradient under different contamination profiles has different values depends on the location and dimension of the pollution region.

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.

Experimental investigation on composite insulators AC flashover performance with fan-shaped non-uniform pollution under electro-thermal stress

Pollution deposition along with ultraviolet (UV) radiation and electro-thermal stress cause the composite insulators to face with critical conditions. The type of pollution which settles on insulators is not only uniform but also it can be non-uniform and uneven. In this study, the results of the uniform and fan-shaped non-uniform (FSNU) pollution tests on four various types of virgin and aged polymeric insulators under AC voltage are presented. To find the effects of accelerated aging on polymer chains of composite insulators, scanning electron microscopy (SEM) is carried out. Based on IEC 60507, the solid layer method is applied to settle pollution on the insulator surface. The results demonstrate that the flashover voltage of virgin and also aged samples decreased when pollution non-uniformity degree (J) increases from 1 to 13. The flashover voltage of studied insulators is reduced by increasing the occupation ratio (K). However, the impact of K was lesser than J on flashover voltage of the polymeric insulators. Investigated polymeric insulators have been aged up to six weeks (1000 h). Although the influence of two weeks (333 h) accelerated aging on flashover voltage and morphology of the composite insulators was not tangible, therefore flashover strength of the samples is decreased while the aging period time increases. Statistical analysis has been done to estimate the flashover voltage of accelerated aged composite insulators under uniform and FSNU pollution based on virgin insulators. The research aimed to select insulators in windy and sunny areas.

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 Performance of RTV Coated Insulators

Theincrease in power demand necessitates the usage of EHV and UHV transmission system. The growth of industries causes higher pollution level in the ambient condition on insulators. This increases the pollution severity of the site which results in pollution accumulation on the surface of Insulators. This causes flashover across insulator. Flashover across polluted insulators poses a serious threat to the reliability of the system and leads to system outages. There are many remedial measures to minimize the flashover of a porcelain insulator under pollution conditions. One such method is the application of hydrophobic coatings such as Room Temperature Vulcanizing Silicone Rubber on the surface of ceramic insulators. Laboratory testing of coated insulators has been carried out based on the solid layer method and by the inclined plane tests at constant voltage to evaluate the RTV coatings withstands capability against tracking and erosion. The performance of the coatings was assessed by monitoring the leakage current on the insulator surfaces. The applied voltage and leakage current were monitored throughout the tests. In order to optimize and economize the usage of RTV coatings various tests were performed and results are analyzed. It was possible to conclude from the test results that one fourth length of RTV coating is sufficient to withstand the pollution severity.

Effects of algae contamination on the hydrophobicity of high‐voltage composite insulators

Algae colonisation has been observed on silicone rubber insulators around the world especially in a subtropical climate because the moderate temperature and moisture could aggravate the growth of algae upon silicone rubber material. The surface of these insulators easily forms a water film, and the originally excellent hydrophobicity is decreased or even destroyed. This study explores the regularity of the hydrophobicity changes and the underlying mechanism. Based on the solid layer method, silicone rubber samples were found with algae and inorganics quantitatively, and their contact angles were measured after reservation under different humidity levels. The results showed that although inorganic ash could accelerate the hydrophobic recovery process, algae colonisation decisively decreased the hydrophobicity, especially in moist climates. After an extensive investigation of biological contaminants, it was found that the appearance of algae was independent of inorganics, but algae could accelerate the accumulation of inorganics through water absorptivity and the viscosity of secretions. The water absorption ability of algae was compared with that of inorganic ash and sugar, and their difference was deduced to be due to the environmental adaptability of the algae organisms, which was reflected mainly in a dry climate. The microscopy analysis of bio-contaminants was conducted through SEM.

Study on the dc flashover performance of standard suspension insulator with ring‐shaped non‐uniform pollution

Under dc electric field, pollution may be more easily deposited around insulator string caps and pins, distributing non-uniformly on its inner and outer parts, and presenting ring-like shape. dc Flashover tests of 7-unit XHP-160 insulator string were carried out. During the tests, the ring-shaped non-uniform pollution was simulated using solid-layer method by changing the ratio I/O of inner-to-outer surface salt deposit density (SDD) and radius (r) of the heavily polluted area (the inner part). On the basis of the test data, the effects of ring-shaped non-uniform pollution on dc flashover characteristics were studied. Then, the relative variation trend of flashover voltage, surface pollution layer resistance, and leakage current were discussed. Research results show that the ratio I/O affects the dc flashover performance of the insulator string. The flashover voltage increases with the increase of I/O. With the increase of the radius r, the flashover voltage will increase at first and then decrease. Under ring-shaped non-uniform pollution, surface pollution layer resistance of insulator will increase, which results in lower leakage current and higher flashover voltage. The results will be of certain value in providing references for outdoor insulation selection.

Influence of Single and Multiple Dry Bands on Critical Flashover Voltage of Silicone Rubber Outdoor Insulators: Simulation and Experimental Study

Dry band formation on the surface of outdoor insulators is one of the main reasons leading to flashover and power outages. In this paper, a dynamic arc model is proposed for single and multiple dry bands configuration to predict the critical flashover voltage for silicone rubber outdoor insulators. An arc is modelled as a time dependent impedance consisting of a Resistor Inductor Capacitor (RLC) circuit. The effect of dry band location and existence of multiple dry bands on critical flashover voltage is investigated. To validate the proposed model, experiments were conducted in a climate chamber under controlled environmental conditions on rectangular silicone rubber sheets polluted using improved solid layer method based on IEC 60,507. Tests were conducted at different dry band configurations and pollution severity levels. A good correlation was found between experimental results and simulation results. This model can provide a good foundation for the development of mathematical models for station post insulators having multiple dry and clean bands and can be used in the design and selection of outdoor insulators for polluted conditions.

Measurement of surface resistance of silicone rubber sheets under polluted and dry band conditions

Ageing and degradation of silicone rubber insulators in contaminated environments is a major concern due to their organic nature. Understanding the flashover process of silicone rubber insulators under contamination is very important and needs standardized tests and procedures. Surface resistance measurement can be used as an indication of ageing and contamination severity of outdoor silicone rubber insulators. This paper presents experimental and mathematical results on surface resistance of high-temperature vulcanized silicone rubber sheets under various environmental and contaminated conditions. Rectangular silicone rubber sheets were polluted artificially in laboratory using a modified solid layer method based on IEC 60507 and tested in a climate chamber where fog rate, humidity and temperature can be controlled. Influence of non-soluble salt deposit density (NSDD), pollution severity, relative humidity, ambient temperature, dry band location and width, and multiple dry bands on surface resistance have been investigated. The obtained results show that surface resistance decreases with increase in NSDD, pollution severity and relative humidity. Increase in surface resistance was observed with the formation of dry bands. Although surface resistance was effected by all parameters, the most dominant parameter was noted down to be pollution severity level and dry band formation. Repeatability of results was confirmed by performing each test five times and concluded that surface resistance measurement can be standardized to evaluate ageing and pollution severity of silicone rubber insulators. These results along with the available literature on equivalent salt deposit density (ESDD) measurement could be used to formulate a relation between ESDD and surface resistance that could be useful for evaluating the performance of silicone rubber insulators in wet and contaminated environments.

Autocorrelation aided rough set based contamination level prediction of high voltage insulator at different environmental condition

This paper presents a Rough Set Theory (RST) based approach for predicting the surface contamination level of porcelain type insulators at different environmental condition. The sample insulators have been contaminated by Solid layer Method (SLM) according to IEC60507. Leakage current of the insulators are recorded at different contamination level and at different humidity conditions. In the proposed method, autocorrelation technique is used for feature selection from leakage current because it is well suited for non-stationary leakage current signals and cancels out the effect of noise present in the signal. Rough Set Theory is used for classification of extracted features as it suits well with the correlation technique. Result shows that the proposed method is able to detect the contamination level with acceptable range of accuracy.

DC flashover performance of ice‐covered insulators under complex ambient conditions

The electrical characteristics of ice-covered insulators in coexisting conditions of high altitude, icing and pollution are a basis for external insulation selection of transmission lines in icing regions. Ice accretion on insulators has been studied for decades, while few studies focus on the flashover performance of ice-covered insulators polluted by two types of contamination, that is the solid layer method and icing water conductivity method, simultaneously. On the basis of the investigations on DC flashover performance of ice-covered insulators in the artificial climate chamber, the influence of different parameters, such as insulator string length, icing water conductivity, salt deposit density as well as atmospheric pressure on DC icing flashover voltage of insulator strings is studied. According to the experimental results, the relationships between the flashover voltage and each of such factors are determined and analysed. Moreover, the correction formula for DC flashover voltage of ice-covered insulators in complex ambient conditions is proposed.

Investigations on AC pollution flashover performance of insulator string under different non‐uniform pollution conditions

Observations of contamination tests showed that, the contamination distribution of insulators is usually uneven. In this study, the solid layer method was used to imitate different non-uniform pollution conditions and the AC pollution flashover tests of 7-unit insulators were carried out. The results indicate that the increase of uneven pollution degree J from 1 to 15 will give a 39% raise of U 50 under non-uniform pollution on top and bottom surfaces, a 23% decrease for fan-shaped non-uniform pollution and a 21% higher U 50 with ring-shaped non-uniform pollution. A higher occupation ratio (k) of leeward side will reduce U 50 under fan-shaped non-uniform pollution and a bigger radius R of heavy polluted area has certain effect on U 50 for ring-shaped non-uniform pollution. The U 50 and salt deposit density still can be expressed by the negative power function, and non-uniform pollution conditions and J have great effect on a, but less impact on n. The correction equations of different non-uniform pollution conditions are obtained and the relative errors are acceptable. The research has certain reference significance for the design and selection of AC transmission line external insulation.

Artificial pollution flashover performance of porcelain long rod UHVDC insulators at high altitudes

Porcelain long rod insulators are recommended for outdoor insulation of UHV/EHV dc transmission lines because of their excellent service experience obtained in Central Europe. However, very few studies have been conducted on dc pollution flashover performance or the UHVDC insulators at high altitudes. Artificial pollution tests on 300 kN and above porcelain long rod insulators were carried out with dc voltage in natural high altitude areas (about 2000 m), in which the solid layer method was used and the 50% flashover voltage (U50%) was measured with the up-and-down method. Test results show that dc pollution flashover performances of the 300 and 400 kN insulators are similar. The exponents characterizing influence of salt deposit density on the flashover voltage vary from 0.46 to 0.57. A nearly linear relationship between the flashover voltage and the string length of the insulators is presented. Both double suspension strings and tension string patterns have a significant influence on the flashover voltage. The influence of non-uniform pollution distribution between the top and bottom surfaces of the insulator sheds on the flashover voltage is analyzed, and a correction coefficient for the insulators is proposed.

AC pollution flashover performance and flashover process of glass insulators at high altitude site

The ac pollution flashover performance and flashover process of LXHY 3 -I6O insulators was investigated at a high altitude site (altitude of 1400m) in this paper. The solid layer method was used, and even-rising voltage method was adopted. According to the test results, the average pollution flashover voltage ( U av ) decreased with the increase of pollution, and there was no obvious relationship between the exponent characterising the influence of pollution and the length of the insulator strings. The relationship between U av and the length of the insulator strings was nearly linear. Subsequently, the effect of the pollution and the length of insulator strings on the critical flashover arc trajectory were analysed. It concluded that the critical flashover distance ( l c ) decreased with the increase of pollution, and it was shorter than the leakage distance ( L 0 ), whereas there was no significant relationship between l c / L 0 and the length of insulator strings. The arc appearance at the high altitude site was very irregular with obvious bending and rocking; the local arcs deviated from the surface of the polluted insulators even more seriously and the diameter was thicker than those obtained in the normal environment. Moreover, the brightness and diameter of local arcs was related to pollution.

Pollution flashover performance of full-scale ±800 kV converter station post insulators at high altitude area

On the background of the peculiar technology problems with the external insulation of UHV dc equipment in China, caused by high altitude and heavy pollution, this paper presents the pollution flashover performance of full-scale ±800 kV converter station post insulators at actual high altitude area. The tests were carried out according to the solid layer method, and the 50% withstand voltage (U50%) was determined by the up-and-down method. The artificial contamination test results indicated that the shed configuration and the rod diameter had a significant influence on the flashover voltages. Shed parameters of one big and one small alternating shed composite post insulator which had superior dc pollution flashover performance had been recommended. The relationship between U50% and insulation height was approximately linear at actual high altitude area for post insulators. It was found that partial discharges occurred at the top section firstly and partial arcs easily appeared at the parts nearby the connecting fittings during the flashover process. And arc floating phenomenon was significantly serious in actual high altitude area. Furthermore, comparison was made between the U50% values of composite post insulators in fog and in rain. The U50% values in fog of composite post insulators were generally higher than that in rain. Thus, the outdoor insulation design of composite post insulators should primarily consider the U50% value in fog. This work thus provides useful reference for the design, operation and maintenance of UHV dc converter stations outdoor insulators in China.

Aging evaluation of silicone rubber insulators using leakage current and flashover voltage analysis

Ultraviolet (UV) radiation decreases the hydrophobicity of silicone rubber (SiR) insulators. Lack of hydrophobicity on the surface of such insulators lowers the flashover voltage and increases the Leakage Current (LC) of insulators in the moist environment. This paper presents the artificial UV radiation effects on three types of 20 kV SiR insulators in a chamber with nine UV-C lamps (50 W/m2) for up to 5000 hours. To simulate the moist environment, solid layer method is applied according to IEC 60507 that includes artificial pollution deposition on the insulator surface. Fast Fourier transform of the LC waveforms indicates that the third and the fifth harmonic components are quite sensitive to any incremental discharge on the insulator surface. This sensitivity makes the frequency spectrum of the LC a good criterion to distinguish three distinct SiR insulator situations under the electric stress: 1) no discharge, 2) dry band arcing/corona discharge and 3) continuous arc. Thermogravimetric analysis (TGA) and scanning electron microscope images depict that the polluted insulators include much larger degraded parts under electric stress after aging. Measurements also show that the flashover voltages and the hydrophobicity of aged insulators decrease as the UV exposure time increases for different levels of moisture and pollution.

Comparison of pollution flashover performance of porcelain long rod, disc type, and composite UHVDC insulators at high altitudes

Aiming at porcelain long rod, disc type and composite long rod UHVDC insulators, this paper presents a comparison of their dc pollution flashover performances and an analysis of arcing behavior at high altitudes (1970m). The solid layer method was used in artificial pollution tests, in which sodium chloride and kaolin powder were used to simulate conductive and inert materials. The insulators were wetted by steam fog in a fog chamber. The 50% flashover voltage (U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50%</sub> ) was measured with the up-and-down method. According to the test results, the three types of insulators are similar in the characteristic exponent which characterizes influence of the salt deposit density on the flashover voltage. Due to lower utilization ratio of leakage distances, pollution flashover voltage gradient for the porcelain long rod insulators is lower than that for the disc type insulators. Whereas covered with Room Temperature Vulcanized (RTV) silicone rubber coatings on the trunk surfaces, the porcelain long rod insulator is much superior to the disc type insulators in pollution flashover voltage gradient. The dc pollution flashover performance and the utilization ratio of leakage distances for the composite long rod insulators are much better than those for the other two types of insulators, which are induced by the special configuration of composite long rod insulators.