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Insulators and auxiliary equipment are used to provide electrical isolation in energy transmission. The high electric field distribution on the composite insulators causes a decrease in the hydrophobicity and increases the aging of the insulator over time. Corona rings are used to balance the electric field distribution with insulators. The corona rings used are designed according to thickness, diameter, and height parameters. In this study, the design parameters of the corona ring used in composite insulators are evaluated by finite element analysis. In this context, different types of corona rings were modeled in real scale in the computer environment and transferred to the Ansys Electronics Suite finite element software program. Analyses were performed with appropriate analysis settings and material definitions. Different design parameters were examined in the analysis, and the results were interpreted and shown in detail in the article. As a result, the necessity of system evaluation with finite element analyses in designing insulation systems used in energy transmission has been demonstrated. [ABSTRACT FROM AUTHOR]

To obtain a more comprehensive knowledge of the surface electric field distribution of composite insulators, a three-dimensional (3D) simulation model of a 10 kV FXBW4-10/70 composite insulator was established, and the distribution of the axial and radial electric fields on the surface of the insulator under normal, damaged, internal defect, and fouling fault conditions were calculated and analyzed based on the finite element method. The results showed that the axial and radial electric field distributions on the surfaces of the normal composite insulators were "U" shaped, the radial electric field at the damaged location had a greater change than the axial electric field, and both the axial and radial electric fields at the internal defect location increased significantly. For the insulator covered with NaCl conductive fouling, the axial electric fields at the high-voltage (HV) and low-voltage (LV) ends showed a greater change. The results can provide a basis for the fault identification of composite insulators and the optimal design of insulation structures. [ABSTRACT FROM AUTHOR]

The rod in the composite insulator is a load-bearing component, and glass-fiber-reinforced plastic (GRP) has always been regarded as the most suitable material. However, the investigation reveals that the performance shortcomings of GRP rods are the main cause of emergency heating defects of 131 new 500-kV ac composite insulators in South China. The finite-element simulation is conducted to understand the potential mechanism of heating. It is demonstrated that the holes with moisture distort the electric field, increasing heating power. A hole with moisture in the GRP rod longer than 500 mm could lead to emergency heating defects with temperature rise exceeding 5 K. For the holes in the GRP rod are formed by adjacent voids, the emergency heating defect is inevitable unless the porosity decreases. The fiber infiltration process of the GRP rods is analyzed on the basis of Darcy’s Law, and an improved process is proposed to reduce porosity. Maintaining the mass fraction of fiber by at least 70% and replacing the damp infiltration fluid in time in the production of GRP rods are necessary to restrain porosity. 300-h water diffusion test with a 50- $\mu \text{A}$ threshold is an effective evaluation method of the GRP rod performance. This method should be used before putting composite insulators into operation. [ABSTRACT FROM AUTHOR]

• Modelling of three-dimensional model of a 220 kV composite insulator and its associated corona ring using COMSOL software. • Investigating the relationship between corona ring design variables and electric field strength. • Bat Algorithm is an innovative method to reduce electric field intensity in critical areas of composite insulators. • Combining Experimental Design Methodology and Bat algorithm can be a powerful tool for optimizing corona ring design. • Achieving a significant decrease in maximum electric field strength. The distribution of the electric field plays a crucial role in evaluating the effectiveness of composite insulators. This research presents an innovative approach for optimizing the design of corona rings, aiming to decrease the electric field intensity in critical areas to satisfactory levels. The investigation examined the correlation among corona ring design variables and the intensity of the electric field close to the energized-end fitting in a 220 kV composite insulator equipped with a corona ring. Using design of experiment methods, the impact of three corona ring design parameters – corona ring diameter (R), ring tube diameter (Dr), and corona ring height (H) – was assessed. A novel nonlinear mathematical objective function was formulated, connecting the electric field magnitude to the structural parameters of the corona ring. Subsequently, the Bat algorithm, a bio-inspired optimization technique, was employed to enhance the initial corona ring design and mitigate the electric field intensity. Finally, the Finite Element Method (FEM) was utilized to simulate and evaluate the voltage distribution and electric field stress. The optimization process resulted in a substantial decrease in the highest electric field magnitude, by 58.6 % compared to the insulator with the threshold value, and 75 % when devoid of a corona ring. Additionally, the research highlighted the significant influence of ring tube thickness on the distribution of the electric field. The combination of experimental design and the Bat algorithm proved to be a powerful tool for optimizing the design of corona rings on transmission line composite insulators, providing precise solutions for optimizing corona discharge problems and enhancing the reliability of power transmission systems. [ABSTRACT FROM AUTHOR]

The present investigation highlights simulation study performed considering the temporal transformation of the electric field from capacitive to resistive. The effect of uniform pollution, single dry-band, multiple dry-bands and non-uniform pollution are studied in detail. The simulation results indicate the effect of surface current can literally decrease the voltage withstand capability of the insulator. The simulations are carried out under time domain so that the simplicity and the physical integrity of the problem is retained. Experimental investigations are conducted to verify the obtained theoretical results. Investigations show that there is substantial decrement of scintillation inception voltage with time, further experimental observations are explained based on the theoretical results that have been derived. Based on the theoretical and experimental observations, it is thought that proper insulation design and optimal creepage should be provided under DC, as field distribution can change over a period with increasing surface conductivity. [ABSTRACT FROM AUTHOR]

Electric field intensity is one of the factors affecting the corona discharge and insulation of high voltage composite insulators. Accordingly, it is necessary to adjust the potential distribution and electric field along the insulator. Using the corona ring on the high voltage side has a great potential to minimize the intensity of the electric field. Since the design and installation conditions of the corona ring can change the electric field, in this paper, Derivative-Free Solvers (DFS) based numerical solution methods are used to obtain optimal parameters. Three-dimensional finite element method (FEM) in COMSOL software is employed to simulate and compute the electric field. Comparison of the results has shown that Derivative-Free Solvers have acceptable speed and good convergence. The parameters obtained from the optimization methods can reduce the electric field by up to %66. According to the results, FEM-DFS hybridization technique could be very helpful in optimization of corona ring design. [ABSTRACT FROM AUTHOR]

Water droplets on the surface of insulators can distort the electric field and cause the generation of surface partial discharge or flashover. In this study, the inception and the development of surface partial discharges on a 110 kV composite insulator were evaluated by using a solar‐blind ultraviolet imager. Several experiments were conducted by using water droplets differing in volume, conductivity, and position on an insulator housing. The results showed that the corona inception voltage decreases with the increasing volume of the water droplets. The relative permittivity of the water droplet decreases with the increase of the conductivity and then reduces the electric field intensity and increases the corona inception voltage. Installing the grading ring can increase the value of the corona inception voltage by 38% at most. To investigate the influence of the water droplets on the corona inception characteristics of the insulator, the sheath and shed models were proposed according to the feature of the electric field distribution. By changing the parameters of the water droplets, the corona inception voltage, discharge position, and electric field were analysed. Furthermore, the flashover voltage of the water droplets is influenced by its conductivity, while the corona inception voltage by its relative permittivity. [ABSTRACT FROM AUTHOR]

The abnormal temperature rise of glass fibre reinforced polymer (GRP) composite in the composite insulator, which has been reported as the early stage of decay-like fractures, has gained significant attention from both industrial and academic sectors. In this study, GRP rod samples, obtained from composite insulators were subjected to hygrothermal ageing and were tested under the conditions according to IEC 62217. The leakage current, partial discharge and temperature rise of the samples were measured. All three parameters tended to increase with the ageing time under AC and DC electric fields. The power contribution supplied by partial discharge could be ignored. Simulation results proved that the temperature rise was mainly caused by the volume current. Under the DC electric field, the conductive current was the heating source, whereas under the AC electric field, the heating power was supplied by both conductive current and the polarisation loss. The content of absorbed moisture in the GRP rod sample showed a linear relationship with the temperature rise. The moisture absorption property can be used as an index to evaluate the ageing state of GRP rod in the composite insulator. [ABSTRACT FROM AUTHOR]

• 3D modeling of 230 kV composite insulator and corona ring in COMSOL software. • 3D Modeling of the tower structure, conductor, hardware, and mutual phases and investigating their effects on the EFI distribution of the creepage distance of the composite insulator in COMSOL software. • Determining the ideal corona ring parameters, such as the diameter, thickness, and installation position. • The use of DFSs such as NM and BOBYQA algorithms in COMSOL optimization software. One of the key elements in lowering the electric field intensity (EFI) on the creepage distance of composite insulators is the usage of the corona ring and its ideal design. First, using the Finite Element Method (FEM) in the 3D COMSOL Multiphysics program, this paper investigated and calculated the changes in the EFI of the creepage distance of the 230-kV composite insulator with and without taking into account the effects of the corona ring, tower structure, conductor, hardware, and mutual phases. Next, the ideal goal function is chosen in order to minimize the insulator creepage distance's maximal EFI. Nelder-Mead (NM) and Bound Optimization by Quadratic Approximation (BOBYQA), two optimization techniques, are used for the best design of corona ring parameters on the 230 kV insulator. Finally, the diameter, thickness, and installation position of the ideal corona ring are determined using the suggested methodologies and different restrictions. The obtained results demonstrate that, in contrast to previous studies that have only focused on a few of the aforementioned constraints, taking into account the tower structure, conductor, hardware, and mutual phases will have a significant impact on the distribution of the EFI on the insulator creepage distance. [ABSTRACT FROM AUTHOR]

The transmission corridors can be effectively saved using 750 kV four-circuit transmission line on the same tower. In order to reduce the corona level, structure optimisation of fittings plays an important role in the transmission line design. In this study, the electric field distribution of 750 kV transmission line on six cross-arms tower was calculated based on finite element method, and the influences of pipe diameter, ring diameter and installation position of the grading ring were analysed. The results show that the increase of pipe diameter can reduce the electric field strength of grading ring while the increase of installation position and decrease of ring diameter are important to protect the end fitting of composite insulator. When using grading ring with the pipe diameter of 100 mm, the ring diameter of 700–900 mm and the installation position of 150–250 mm, the electric field strength can be controlled in a reasonable range. These results can provide references for the grading ring design of 750 kV four-circuit transmission line on the same tower.

The transmission corridors can be effectively saved using 750 kV four-circuit transmission line on the same tower. In order to reduce the corona level, structure optimisation of fittings plays an important role in the transmission line design. In this study, the electric field distribution of 750 kV transmission line on six cross-arms tower was calculated based on finite element method, and the influences of pipe diameter, ring diameter and installation position of the grading ring were analysed. The results show that the increase of pipe diameter can reduce the electric field strength of grading ring while the increase of installation position and decrease of ring diameter are important to protect the end fitting of composite insulator. When using grading ring with the pipe diameter of 100 mm, the ring diameter of 700–900 mm and the installation position of 150–250 mm, the electric field strength can be controlled in a reasonable range. These results can provide references for the grading ring design of 750 kV four-circuit transmission line on the same tower. [ABSTRACT FROM AUTHOR]

Abstract This paper presents measurements and calculations of electric field in samples with deliberately planted superficial and internal defects. Samples evaluated include full-scale composite insulators and cylindrical rods of the housing material. The goal of this work is to ascertain the viability of electric field as an indicator of impending failure of composite insulators that can develop such defects during manufacture and/or service. Measurements were performed with an Electro-optic probe based on Pockels effect. Calculations were performed using 3-dimensional Boundary Element Method package. Good agreement between the measurements and calculations has been demonstrated. The results show that conducting defects originating from the HV electrode produce a greater change in the electric field when compared to a healthy insulator than defects originating from the ground electrode or anywhere in between. The magnitude of the change in electric field when compared with a healthy sample diminished with increasing radial distance from the sample. Hence, it is important that the probe be placed close to the insulator shank for maximizing defect detection. [ABSTRACT FROM AUTHOR]

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In recent years, the local temperature rise of composite insulators has become a serious problem. In this paper, the temperature rise characteristics of the insulators at different humidity were studied at first in the laboratory. High humidity was found to be the prerequisite of temperature rise. Then the electrical characteristics of temperature rise area were analyzed. The housings of samples showed different surface currents under AC and DC electrical field. The temperature rise of the sample caused by the surface current was simulated and calculated afterwards. It was proved that the temperature rise of the housing was caused by the surface current. Finally, a temperature rise model of the housing was established. Dielectric loss in the surface layer of the silicone rubber induced by moisture is the primary factor that caused temperature rise on field-aged composite insulator housings. [ABSTRACT FROM AUTHOR]

There has been a growing concern over recent years regarding the phenomenon of local heating of composite insulators. In this paper, the influences of humidity, contamination and local electric field on the temperature and dielectric properties of field-aged insulators were studied experimentally. Aging of the silicone rubber (SIR) material on the weathershed surface, rather than resistive current flow from contamination, was found to be the major cause of local heating observed by thermography. The aged SIR material exhibited strong dielectric loss under high localized AC electric field and high relative humidity. A hypothesis was developed to mitigate the moisture induced local heating on composite insulators. [ABSTRACT FROM AUTHOR]

The shed configuration has obvious effects on the flow field characteristics and electric field distributions around composite insulators, and then impacts their icing flashover performance. In this study, the AC flashover comparative tests for 12 types of 220 kV composite insulators with different shed configurations under non-energized and energized ice accumulation conditions are conducted in the artificial climate chamber. The influences of shed configuration on icing flashover voltages and flashover arc paths are analyzed. Results indicate that with the increase of the icing stress, both the flashover arc path and the ratio of the air gap arc gradually decrease. These variations lead the icing flashover voltage to gradually decrease and then approach to saturation. For ice-covered composite insulators with different shed configurations, the ratios of the air gap arc to the total flashover arc are different due to the differences of their shed spacings, icicle lengths, differences of shed diameters, (extra) large shed diameters. These result in the differences of icing flashover voltages and their characteristic exponent c describing the influence of ice thickness. Besides, for insulators iced under energized condition, their icing flashover voltages and flashover arc paths are different from that under non-energized condition. Hence, the energized icing test, which is also the only normative reference of icing test proposed by the IEEE standard, should be carried out to optimize the shed configuration of composite insulators used in ice areas. [ABSTRACT FROM AUTHOR]

This paper is aimed at numerical simulations and experiments on the coalescence of pairs of sessile water droplets deposited on dielectric composite insulating surfaces. The mechanisms as well as parameters involved in coalescence under the influence of DC electric field are investigated. A mathematical approach based on a diffuse interface model that essentially consists of a coupling between Navier-Stokes equations, the computing of electric force and a Cahn-Hilliard type equation describing the interface evolution including capillary phenomena, is developed. Experiments are performed to analyze the behavior of these water droplets depending on their size, conductivity and location with respect to electrodes as well as the hydrophobicity of insulator. Simulations showed reasonably good agreement with the experimental data. It also showed that the coalescence process depends mainly on three parameters: the location of the droplets on the insulating surface, the volume of the droplets and the distance between droplets. [ABSTRACT FROM AUTHOR]

Corona rings can improve the insulation performance of insulator strings because of their electric field grading property or can decrease the insulation performance due to their arc clearance reduction property. The resulting insulation performance of the string which is under the influence of those two conflicting effects depends on the corona ring parameter settings. Therefore, a detailed experimental work is required to determine the insulation performance for different types of test voltages under different ambient conditions. This paper presents the results of experimental studies regarding the effects of corona rings on the insulation performance of 380 kV non-ceramic V-insulator strings. Those effects and flashover routes were determined for lightning impulses, switching impulses and AC voltages. Corona ring diameter, corona tube diameter, and mounting height were selected as the ring design parameters. Experimental studies were performed for the strings including corona rings of different design parameters as well as for the ring free strings. Test results were discussed from discharge development physics point of view and optimal configuration was determined for the strings. [ABSTRACT FROM AUTHOR]

In this article, analysis of electric field stress and electric potential distributions of a 33-kV composite insulator and factors that affect the electric field are discussed. Accordingly, the article is classified into two parts. In the first part, the designs of three different configurations of non-ceramic (composite) insulator based on their geometry modification in end fittings and water shed are discussed. The electrical performances are analyzed using electric field and electrical potential distribution. In the second part, a reduction of the electric field near the end fittings is done to control the electric field stress intended for long-term performance. For that, the grading material is placed between the core and housing materials by fitting the arcing horn near the end fittings. A 33-kV composite insulator is modeled in two dimensions by the finite-element method to investigate the electric field and electric potential distribution under normal and polluted conditions. The results reveal that an optimum installation of an arcing horn at the high-voltage end in the composite insulator with silicone rubber overlapping the edges of metal end fittings made a significant reduction in electric field stress on 33-kV non-ceramic insulators. [ABSTRACT FROM AUTHOR]

The grading ring (GR) can adjust the potential distribution along the composite insulator and reduce the electric field (E-field) strengths near its end fittings. However, little research has been conducted about the effects of GR on the insulation performance of composite insulators under icing condition. Therefore, the ac icing flashover performance of two kinds of 220 kV composite insulators under different GR arrangement patterns are tested in the artificial climate chamber. Combining with the numerical simulation, the effects are analyzed. The results indicate that when GR is installed at the high voltage (HV) end, the E-field strength close to the end fitting and the icing uniformity on the whole insulators are both improved. These cause the effect of icing degree on the icing flashover voltage to be larger than that without GR at the HV end. When GR is installed at the grounded end, the perpendicular icicles on the GR will impact the flashover arc path, which causes the icing flashover voltages to be lower than that without GR at the grounded end. When different GRs are only installed at the HV end, the characteristic exponents b (characterizing the influence of freezing water conductivity on icing flashover voltage) are all larger than that without GR. Moreover, the value of b increases with the decrease of GR?s diameter and with the raise of GR?s height. But b changes slightly when there are variations in GR?s pipe diameter and structure. The research can provide reference for the application of GR for 220 kV composite insulators in icing regions. [ABSTRACT FROM PUBLISHER]

The energized icing of composite insulators has been studied by the researchers around the world, but not much about the effects of electric field distribution on their icing and flashover performance. For this purpose, the ice accretion and flashover performance of 220 kV composite insulators with two shed configurations on occasions of different electric field distributions considering the effect of grading rings are analyzed in this paper. The test results indicate that the intensity and homogeneous distribution of electric field have positive effects on the appearance, density and weight of ice; the improvement of electric field distribution after installing grading ring has more effects than the icing characteristics, such as quality, density as well as appearance of ice, on flashover voltages of ice-covered composite insulators; the icing flashover voltages are increased by the improvement of electric field distribution and the increasing ranges of icing flashover voltage were relied on shed configuration. Icing accumulation patterns have less effect on flashover performance of composite insulators with alternatediameter or widely spaced shed configurations. [ABSTRACT FROM AUTHOR]

Serious corona discharges occur on some grading rings of 500-kV compact transmission lines in China owing to defects in the structural design. The noise of the corona is heard clearly even 50 m away from the tower. In order to solve this problem, we have optimized the structure of the grading rings to suppress the corona. In this study, the grading rings that had serious corona discharges were identified and observed with an ultraviolet imager (UVI), and the electric field (E-field) distributions of the grading rings were calculated by means of the three-dimensional finite element method. Based on an analysis of the areas on the grading ring where excessive high E-field magnitudes were observed, we optimized the structures of the grading rings to improve the field distributions on their surfaces. Based on the optimization suggestions, new grading rings were manufactured to replace the old ones. UVI observations showed that the new grading rings could effectively prevent the occurrence of corona discharge. [ABSTRACT FROM AUTHOR]

The electrical performance of composite insulators with adhered ice is less than that of porcelain or glass insulator strings, which is mainly caused by the shed configuration differences. In this paper, the shed con-figuration optimization for ice-covered Extra High Voltage (EHV) composite insulators is discussed in order to improve the electrical performance of ice-covered composite insulators. The effects of the position and length of the air gaps on the electric field distribution of ice-covered composite insulators are investigated and analyzed based on the electric field calculation model. The basic optimization principles of the shed con-figuration for ice-covered composite insulators are based on the electric field calculation results. Moreover, the artificial icing flashover tests on the ice-covered composite insulators with different shed configurations were carried out in artificial climate chamber, and the flashover path was recorded by a high speed cam-era. According to the flashover voltage and the flashover path of composite insulators with different shed configurations, it can be concluded that the composite insulators with large shed spacing and various shed diameters have better electrical performance and can be used in the transmission lines across the icing area [ABSTRACT FROM AUTHOR]

This paper provides an overview of the electric field (E-field) distribution on transmission line composite insulators applied in alternating current applications. Factors that affect the E-field distribution are discussed as well as the influence of the E-field distribution on the short and long term performance. Modeling and measurement methods are reported and examples of calculated E-field magnitudes determined are presented together with corona ring application information. This paper was developed by the IEEE Task Force on Electric Fields and Composite Insulators. [ABSTRACT FROM AUTHOR]

Considerable work has been done on the live detection of faulty elements in the insulators of overhead ac transmission lines but very little on their dc equivalents. One method that has proved successful for the ac case is the measurement of the electric field along the insulators, parallel to the axis and at the rims of the sheds (composite insulators) or of the insulators in a string (porcelain insulators). The dc transmission-line voltage will always include ripple; therefore, it was considered possible that the field due to the ripple component, the "harmonic electric field," could be used in a similar manner. This has proven to be the case as demonstrated by the results of the experiments, both in the field and the laboratory, which are presented in this paper. Field measurements showed that the harmonic electric field could be measured under live conditions and provide repeatable results, both on composite insulators and on porcelain insulator strings. Laboratory measurements of the harmonic electric field were made along healthy composite insulators and some with artificial faults, and along strings of healthy porcelain insulators and strings with a faulty insulator included. The results of laboratory experiments showed that the faults could be identified and located effectively. [ABSTRACT FROM AUTHOR]

Through spatial electric field monitoring, it is expected to realize insulator pollution condition monitoring and contamination flashover warning in a non-contact way. Therefore, in this paper, the spatial electric field distribution characteristics of 110 kV composite insulators are simulated, where the effects of different surface states and their discharge levels on the spatial electric field of insulators are analyzed. On this basis, a non-contact monitoring method for composite insulator pollution based on the spatial electric field is proposed. The results show that there are significant differences in the spatial electric field of the composite insulator among three conditions, namely cleaning, pollution layer wetting, and dry band arcing. Increases of pollution layer wetting and dry band arcing would lead to an increase of the amplitude of the spatial electric field of the insulator. Verification experiments well indicated that it is feasible to identify the degree of pollution layer wetting as well as dry band arcing of the insulator string by fixed-point monitoring, the spatial electric field signal at the cross-strand of d = 0.5 m and directly opposite the last three positions. Research results can provide references for the online monitoring of overhead line polluted insulators and its flashover warning. [ABSTRACT FROM AUTHOR]

This paper modeled the dry band formation and arcing processes on the composite insulator surface to investigate the mechanism of dry band arcing and optimize the insulator geometry. The model calculates the instantaneous electric and thermal fields before and after arc initialization by a generalized finite difference time domain (GFDTD) method. This method improves the field calculation accuracy at a high precision requirement area and reduces the computational complexity at a low precision requirement area. Heat transfer on the insulator surface is evaluated by a thermal energy balance equation to simulate a dry band formation process. Flashover experiments were conducted under contaminated conditions to verify the theoretical model. Both simulation and experiments results show that dry bands were initially formed close to high voltage (HV) and ground electrodes because the electric field and leakage current density around electrode are higher when compared to other locations along the insulator creepage distance. Three geometry factors (creepage factor, shed angle, and alternative shed ratio) were optimized when the insulator creepage distances remained the same. Fifty percent flashover voltage and average duration time from dry band generation moment to flashover were calculated to evaluate the insulator performance under contaminated conditions. This model analyzes the dry band arcing process on the insulator surface and provides detailed information for engineers in composite insulator design. [ABSTRACT FROM AUTHOR]

During ultra high voltage (UHV) transmission, the discharge caused by high intensity electric fields aggravates the aging process of external insulation materials used for composite insulators. The microstructural characteristics of its base material polymer—methyl vinyl silicone rubber—are the key basis for the performance of insulation materials under electric field exposure. Based on molecular dynamics simulations, a molecular model of methyl vinyl silicone rubber was established. Mechanisms influencing the microstructure evolution under electric fields had been studied at the atomic level. The results showed that the initial reaction characteristics of silicone rubber molecules involve the violent vibrated of all the methyl and vinyl atoms, and shortening of the chemical bonds. The neighboring groups were close to each other and generated different amounts of -Si-Si- bonds. This promoted the helical shrinkage of the molecule, and protrusion of the middle of the molecule which presented an inverted U shape. The high electric field greatly reduced the total energy of molecules, and the potential energy in particular was more severely destroyed, resulting in degradation of its structure. Besides, as the electric field intensity increased, the elastic modulus of the molecule gradually increased. It was shown that high electric fields would make the stiffness of silicone rubber become larger, and the brittleness to become stronger, which reduced the mechanical properties of materials, accelerating its aging. The results provide a theoretical basis for establishing the connection between the micro appearance and macro characteristics of materials, as well as reference values for the optimization of base materials used for making composite insulators. [ABSTRACT FROM AUTHOR]

In the paper, a new approach is proposed to improve the outdoor insulation properties of transmission lines. It is achieved by installing the insulation jackets and additional grading rings onto transmission line conductors. The impact of insulation jacket parameters on the electrical field distribution along a 220 kV composite insulator was simulated by a finite element program assuming dry surface contamination. The corona inception voltage was measured on real composite insulators and the measurement results verified the conclusion from the simulation. Furthermore, the correlation between the insulation jackets? length and the contamination flashover voltage of composite insulators was studied. Based on the measurement and simulation results, the optimal insulation jacket parameters are suggested. In the last part of this paper, insulation jackets manufactured according to the optimal parameters are installed onto the transmission line conductor in the field. During one year of operation, the positive effect on the electric field distribution and the reliability of the installed insulation jackets have been confirmed. [ABSTRACT FROM PUBLISHER]