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To enhance the surface insulation properties of SiO2/epoxy resin composites, the SiO2 filler is co-modified with a chemical method and dielectric barrier discharge plasma in this work. The effects on the micro-structures, electrical parameters and surface insulation properties of the materials are studied. The results show that chemical modification using the silane coupling agent (KH550) can effectively introduce organo-functional groups into SiO2 filler. On the other hand, plasma modification shows little effect on the organo-functional group but significantly increases the dispersity of the nanoparticles, therefore reducing filler conglobation in epoxy resin composite. The composite samples with SiO2 doping concentration of 1 wt.%, 2 wt.%, 3 wt.%, 5 wt.% and 7 wt.% are prepared and characterized. It is found that the synergy of chemical and plasma methods could significantly improve the surface insulation of composite samples. Through doping 2 wt.% of the co-modified SiO2 filler, the direct current flashover voltage of the composites in dry air at atmospheric pressure can be increased to 1.53 times of the pure epoxy. The enhanced surface insulation properties are explained by the trap effect and the change of electrical parameters through the co-modification process. [ABSTRACT FROM AUTHOR]

Gas insulated switchgear may be exposed to AC-DC mixed voltages in bipolar high voltage direct current (HVDC) systems. To improve the insulation performance of the epoxy insulator, this paper develops the multi-dimensional functionally graded materials (MFGM), which combines the bulk permittivity graded materials (ϵ -FGM) and the surface nonlinear conductivity materials (SNCM). The ϵ -FGM bulk and the SNCM layer of the MFGM insulator were prepared by the layer-by-layer pouring method and the air spraying technology. Results show that the electric field strength of the MFGM insulator around the HV triple junction is reduced by over 37% and 39% under AC and DC voltages. Compared with the uniform insulator, the AC and the DC flashover voltages of the MFGM insulator are raised by 17.5% and 27.5%, respectively. The MFGM insulator can adapt to both stationary and transient conditions, and thus has a promising application in HVDC compact gas-insulated apparatuses. [ABSTRACT FROM AUTHOR]

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

In this article, the influence of polishing orientation on surface charge accumulation and flashover characteristics of the basin spacer in a downsized dc-gas insulated transmission line (GIL) are explored by experiments. Results show that the surface charge distribution of the polished spacers is different from the untreated one. Heteropolar charges can be observed in the polished area and outward expansion area under prestressing condition. The flashover voltages of all polished spacers are decreased. The radial polishing (RP) has the greatest impact on the flashover voltage, and the flashover voltage of the radially polished spacer is decreased by 11% under positive prestressing condition. The metal dust adsorptions of the spacers are also measured, which shows that the radially polished spacer is easier to absorb metal dust and the metal dust diffuses in the radial direction. SEM and energy spectrum scanning of different spacers show that there are more exposed alumina particles on the surface of the polished area. The microdischarge induced by alumina particles is the source of heteropolar charges. When the polished area of the spacers is repaired with epoxy paint, heteropolar charges disappear on the surface of the repaired spacer. It is confirmed that charge accumulation and flashover along the spacer surface are mainly affected by the change of surface morphology on the polished area. [ABSTRACT FROM AUTHOR]

A polypropylene (PP) film is usually employed as the main insulation of the peaking capacitor, which is important in an electromagnetic pulse simulator to generate high-amplitude nanosecond pulse. The flashover voltage of PP films under nanosecond pulse limits the highest working voltage of a peaking capacitor. Surface fluorination was employed to increase the flashover voltage of PP. The flashover voltages of PP samples with different fluorination times (0, 4, and 6 h) were tested in an oven with nanosecond pulse voltage. The results showed that the flashover voltage of the PP film with 6-h surface fluorination was increased about 15% than the untreated film in the air. To clarify the influential mechanism, the physicochemical properties of PP film samples were tested and characterized. The results of thermally stimulated depolarization current (TSDC) showed that the trap density of the PP film increased obviously after fluorination treatment. With the increase in treatment time, the trap depth and density were increased obviously. The surface conductivity of PP films slightly decreased with the increase in fluorination time. The mechanism of surface fluorination on the influence of the flashover performance of the PP film under nanosecond pulse is discussed. It is concluded that surface fluorination significantly increases the carbon–fluorine (C–F) bond of the PP film, resulting in the increase in the depth and density of the surface trap, and then, a large amount of homocharges trapped in the surface trap reduces the electric field near the electrode. [ABSTRACT FROM AUTHOR]

This paper proposes training an artificial neural network (ANN) by a particle swarm optimization (PSO) technique to predict the flashover voltage of outdoor insulators. The analysis follows a series of real-world tests on high-voltage insulators to form a database for implementing artificial intelligence concepts. These tests are performed in various degrees of artificial contamination (distilled brine). Each contamination level shows the amount of contamination in milliliters per area of the isolator. The acquisition database provides values of flashover voltage corresponding to their electrical conductivity in each isolation zone and different degrees of artificial contamination. The results show that ANN trained by PSO can not only provide better prediction results, but also reduce the amount of computation efforts. It is also a more powerful model because: it does not get stuck in a local optimum. In addition, it also has the advantages of simple logic, simple implementation, and underlying intelligence. Compared to the results obtained by practical tests, the results obtained present that the PSO-ANN technique is very effective to predict flashover of high-voltage polluted insulators. [ABSTRACT FROM AUTHOR]

Superhydrophobic (SH) and superamphiphobic (SAP) coatings have been viewed as an alternative to conventional hydrophobic room temperature vulcanizing (RTV) silicone rubber coatings in anti-pollution flashover application. However, being one of the most important properties in RTV-based anti-flashover materials and devices, the hydrophobicity transfer property was rarely documented for SH and SAP coatings, which restricts their practical applications in environments with heavy contamination. Herein, we propose for the first time a superhydrophobicity transfer effect in superwetting (SW) coatings (e.g., SAP and SH coatings) containing low-surface-energy molecules (e.g., polydimethylsiloxane (PDMS)) as a migratory reagent. When the surface is stained by artificial simulated pollutants, PDMS molecules can migrate from the coating to the contamination layer, followed by a surface modification. Through this process, the surface wettability of the contaminant layer gradually evolves from superhydrophilicity to hydrophobicity, and finally to SH state. This evolution is investigated in relation to the amount and species of migratory reagents, migration time, pollution grade, and pollutant species. The superhydrophobicity transfer effect offers the coated glass insulators an outstanding anti-pollution flashover strength. This work can provide a novel and universal protocol to realize a superhydrophobicity transfer property in SW coatings, which may stimulate further investigation and applications in not only anti-pollution flashover but also other fields such as anti-fouling and anti-icing. • Superhydrophobicity transfer effect is proposed for the first time. • Superwetting coatings with superhydrophobicity transfer property are obtained. • The mechanism behind the superhydrophobicity transfer effect is proposed. • Superhydrophobicity transfer effect improves the anti-pollution flashover strength of insulator. [ABSTRACT FROM AUTHOR]

Alumina/epoxy resin (Al2O3/EP) composite material is widely used in the manufacture of insulators. However, the operation environment of long‐term high‐voltage direct current will destroy Al2O3/EP surface insulating performance. In this article, Al2O3/EP was modified by atmospheric pressure Ar and Ar/CF4 plasma jet, and its aging effect was studied by investigating the physicochemical characteristics and the electrical performances of the sample 0 ~ 100 days after modification. The experimental results show that after plasma treatment the surface roughness of the material increases; the O/C ratio on the surface of the material increases after Ar treatment, and the F element is grafted on the surface after Ar/CF4 treatment. These changes lead to the increase of surface energy and hydrophilicity, and the improvement of electrical performance. The surface properties change within 100 days owing to the oxidation reactions and the variability of recombination chemical bonds and molecular chains after high‐energy plasma treatment. The surface O/C ratio of the materials treated by Ar plasma is obviously reduced, the hydrophobicity is restored to some extent, and the electrical properties are also obviously weakened. In comparison, the properties of Ar/CF4 plasma‐modified materials do not change significantly. [ABSTRACT FROM AUTHOR]

In recent years, dry‐type air‐core reactors have frequently experienced inter‐turn short circuits due to the aging of the inter‐turn insulation. In this paper, we prepared epoxy/glass fiber samples and carried out an accelerated thermal aging test up to 840 hours. In different stages of aging, we tested the surface insulation properties, dielectric properties, thermal and mechanical properties of the samples. The results show that: Flashover voltage drops significantly, and when aging for 35 days, it has dropped by 12.4%. This is because aging is accompanied by the conversion of shallow traps to deep traps and the reduction of conductive channels, which slows down the charge dissipation rate and decreases the flashover voltage. Dielectric, thermal, and mechanical properties also show a deteriorating trend. Through the analysis of the changes in thermal and mechanical properties, it is inferred that thermal aging will damage the epoxy matrix more than the glass fiber. In addition, combined with the scanning electron microscope, Fourier transform infrared spectrometer, and X‐ray photoelectron spectrometer characterization results, we believed that the main reason for the material deterioration is the detachment of the glass fiber and the break of the long chain of the matrix. This article has certain reference value for the subsequent engineering application and online monitoring of this material. [ABSTRACT FROM AUTHOR]

To investigate the high-altitude electromagnetic pulse (HEMP) immunity of electrical equipment in operation, a 10-kV transmission line (TL) experimental platform is built in this paper. The conducted transient electromagnetic disturbance (TED) could be injected to the electrical equipment of 10-kV TL with power on or power off. The TED is produced by the pulsed current injection (PCI) generator, whose rise time is less than 20 ns and full width at half maximum is in the range of 500 ∼ 550 ns on short-circuit state with 60 Ω resistor. On the other hand, the 10-kV TL is equivalently designed in cross section to make its characteristic impedance being 330 Ω to conform to the value of practical case. The voltages and currents applied on the tested equipment can be measured at nano-second level simultaneously, which are of great use to learn the effect mechanisms and compare the results under different working conditions. Some 10-kV pin-type porcelain insulators are tested under different conditions, which shows the capacity of the proposed platform to test immunity of 10-kV electrical equipment. [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]

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. [ABSTRACT FROM AUTHOR]

In power system, the post-insulator is a critical apparatus which carries the conductor and also provides isolation between the conductors as well as ground. Besides, it offers mechanical support. However, extreme weather and pollution cause post-insulator flashover, which results in interruption of power supply and revenue loss. Therefore, post-insulator's pollution flashover study is necessary. The pollution flashover voltage (FOV) is directly related to dominating metrological circumstance and how this pollution severity on the surface of insulator. Mostly, anti-pollution flashover coating is deliberated to be one of the most effective means to prevent and reduce pollution flashover. This paper investigates and compares the application of Epoxy Resin and Room Temperature Vulcanize (RTV) Silicone Rubber for enhancing the performance of ceramic outdoor (near coastal thermal plant area) insulator to defeat the effect of environmental pollution. At first, a real-time pollution performance has been carried out in controlled laboratory setup. It shows that the withstand ability of post-insulator has been 25% with Silicone Rubber coating. Subsequently, Artificial Neural Network (ANN) has been used to predict the FOV of post-insulator under wet and dry condition. It shows that critical FOV has enriched with anti-reflection coating rate. After that, post-insulator has been modeled by COMSOL multiphysics software, which is used for estimating field distribution on post-insulator. From the modeling, we found that anti-reflection coated post-insulator surface has low electrical stress than that of others. [ABSTRACT FROM AUTHOR]

Alumina/epoxy composites are widely used in the manufacture of basin insulators, but their surfaces tend to accumulate charges under the high‐voltage direct current (HVDC), which induce the decline of surface insulating property. In this article, the modification method of depositing ZrO2 film sprayed by plasma atomization was proposed to improve the surface insulation performance of the material. Argon was used as the plasma discharge gas, and ZrO (NO3)2.xH2O was used as the zirconium source. The morphology, surface roughness and the element content of materials were measured, and the surface conductivity, flashover voltage, and charge characteristics of the treated samples were tested. The experimental results displayed that a zirconia film was formed on the epoxy resin surface, which restrain the accumulation of surface charges. The surface conductivity of the modified sample was improved by 3 to 4 orders of magnitude, and the flashover voltage was increased by 20%. Studies have shown that: ZrO2 film sprayed by plasma atomization can improve the insulation performance of epoxy resin surface, and it provides an effective method for the surface modification of insulating materials. [ABSTRACT FROM AUTHOR]

In this paper, a novel procedure is put forward to fabricate epoxy insulators with surface functionally graded material (SFGM) with optimized surface conductivity as obtained from the field non-uniformity and the leakage current. For fabrication, a temperature control system is employed to form a spatial temperature gradient, thus regulating fluorination from top to bottom of the insulator surface. Flashover tests are reported under DC voltage, and with DC voltage with polarity reversal; the results show the effectiveness of the SFGM to improve the performance of the insulator. A trap distribution and carrier transport model are utilized to analyze the improved flashover characteristics. [ABSTRACT FROM AUTHOR]

Calcium 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. [ABSTRACT FROM AUTHOR]

This study presents a dynamic arc model of a polluted insulator based on the formulation of the Obenaus model and the Hampton criterion for discharge propagation. An experiment was conducted on a practical glass insulator installed in the Algerian network for the purpose of measuring the flashover voltage and estimating the arc parameters (A and N) using a genetic optimisation algorithm. The parameters used in the dynamic model were the arc current, arc length, and arc resistance calculated using MATLAB. Moreover, an attempt was made with finite element software to calculate the voltage and electric‐field throughout the insulator surface with and without the presence of contaminants. Finally, the obtained simulation and experimental results showed high performances under operational conditions and respect IEC 60060‐1 standard recommendations. [ABSTRACT FROM AUTHOR]

• Effects of asymmetrical distributed algae contaminates of flashover characteristics were evaluated quantitatively based on triangle plate model. • At continuous algae column condition, radial growth ratio of algae played an important role in the decreasing of flashover voltage, because insulator surface transferred into hydrophilic and insulation resistance of the specimens plummeted after algae colonization. • At intermittent algae column condition, axial growth width negatively affected the flashover voltage. Polymer insulators are reported to be contaminated by algae in tropical and subtropical climates around the world. Here, the biological contaminates were sectorial distributed on the insulator surface, stretching from the edge of the shed to the interior section near the core. The radial growth ratio and axial length of the algal column was varying under different environmental conditions. To explore the flashover characteristics under these conditions, the triangle plate model was established, in which algal colonization varied in radial growth ratio and algal column length quantitatively, and the inorganic pollutants were divided into three pollution degrees. The results showed that the increasing algal distribution gradually decreased the flashover voltage, whereas when the algal column was too slender, the flashover voltage increased. Meanwhile, the arc tended to elongate within the bio-contaminated area, and the flashover voltage significantly decreased when the algal column nearly covered the full specimen. Furthermore, surface conductivity and pollutant resistance were theoretically deduced from the Obenaus model, the results of which coincided with the calculated value from the flashover measurements. The change in discharge characteristics was attributed to the loss of hydrophobicity. This research could provide valuable information for the maintenance of bio-contaminated insulators in transmission lines of power systems. [ABSTRACT FROM AUTHOR]

The elevated temperature in operating capacitors speeds up the transportation of charges and causes the flashover to occur easily. Direct fluorination was used to modify the polypropylene film applied as capacitor dielectric, and behaviors of surface charging and flashover voltage at different temperatures were investigated. The surface morphology, functional groups and elemental composition of polypropylene film before and after modification treatment were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray analysis (EDAX), respectively. The surface charging behaviors were analyzed by the surface potential decay (SPD) method at temperature varying from 293 to 353 K. The flashover voltage was analyzed by the view of surface charge and trap characteristics. A thin layer of fluorination which changed the surface state of polypropylene film was formed, which can effectively inhibit the surface charge injection and accumulation at different temperatures. Shallow traps were introduced by the surface molecular structure modification, which was confirmed by the simulation of three-dimensional (3D) electrostatic potential and density of states (DOS). The modification of surface molecular structure, which suppresses the accumulation of surface charge leading to the inhibited distortion of electric field, effectively increased the flashover voltage at different temperatures. • Surface charging and flashover decline the performance of power capacitor. • A fluoride layer of -(CFn) is formed on the polypropylene film after treatment. • Charge injection and flashover are inhibited by the newly introduced shallow traps. • The simulation of 3D electrostatic potential and DOS confirms the speculation. [ABSTRACT FROM AUTHOR]

Electric field optimization plays a significant role in the insulation design of gaseous insulated pipeline (GIL) for the DC power system. Functionally graded material (FGM) with spatial distribution of conductivity σ (σ-FGM) provides a potential method to uniform the electric field and thus reduces flashovers to some extent. However, researches at present are nearly at a standstill for the complicated fabrication techniques and huge bulk conduction losses. In this paper, a novel cone-type insulator with surface conductivity gradient was proposed based on direct fluorination treatment. Theoretical analysis shows that the electric field distortion near the high voltage electrode can be effectively suppressed with increasing the thickness and conductivity of the fluorinated layer. Epoxy cone-type insulators with homogeneous and graded surface conductivity were then prepared by different fluorination treatments to verify the effectiveness of σ-FGM design. As for the homogeneously fluorinated cone-type insulators, the DC flashover characteristics were improved with the rise of fluorination time. Especially, the flashover voltage of the insulators with σ-FGM layers can be raised by up to 36.3 % compared with that of the traditional ones, owing to a more uniform electric field distribution. Theoretical and experimental results prove that the insulator with surface σ-FGM is a promising choice for DC compact GIL. [ABSTRACT FROM AUTHOR]

As an important part of pulsed high-current launcher, insulator takes the functions of electrical insulation and support. Surveys were conducted after multishot to analysis matrix damage and insulation performance of insulator based on a medium-caliber and high linear current density launcher. Mechanical damage of matrix is mainly related to local current. The most serious damage located at zone of flattop and initial decline stage. In addition, serious damage may be caused by sprayed molten aluminum rather than high-temperature plasma. Metal contamination is dominated by local current and contact condition of rail–armature. There are more metal deposits on surface of high current and high muzzle voltage zones, and corresponding flashover voltages decrease significantly. Considering the effect of different damage forms and the operation conditions, the main damage form is matrix ablation located at the contact position of rail–insulator rather than the degradation of electrical insulation. Moreover, the main damage form of bore insulators is different for variety of caliber and linear current density launchers. Insulation damage may be considered mainly in small-caliber and low linear current density launcher, while mechanical damage may be considered mainly in large-caliber launcher and high linear current density launcher. [ABSTRACT FROM AUTHOR]

The aim of this work is to estimate the flashover voltage of cap‐and‐pin insulator using a novel improvement of the pollution resistance evaluation. In cap‐and‐pin suspension insulators, local arcing starts around the pin where the dry bands first appear due to the evaporation of the conductive layer. In appropriate conditions, a unique dominant arc starting from the pin propagates toward the cap resulting in a complete flashover. Since the highest current density is concentrated around the arc root during propagation, the pollution layer residual resistance variation, with respect to the arc position, is non‐linear. Thus an original three‐dimensional model, which depicts a real insulator using COMSOL MultiphysicsTM to evaluate the residual resistance, is developed. This model takes into consideration the actual geometry of the insulator and the current restriction at the arc root for a specific arc radius. A novel mathematical model for calculating the residual resistance of this polluted insulator was elaborated for all possible arc radii. The mathematical model and the 3D simulation results are in satisfactory agreement. To evaluate the flashover voltage, a new approach based on Saddle Point Finding Method is proposed. The new approach and model have been validated using experimental results of previous studies. [ABSTRACT FROM AUTHOR]

Superconducting magnet is one of the core components of international thermonuclear experimental reactor (ITER). Due to the harsh operating environment, for the sake of ensuring the stable operation of the superconducting magnet, the superconducting magnet insulation is required to have excellent electrical and irradiation resistance. However, pure epoxy resin is difficult to adapt to the harsh environment in the ITER, so it needs to be modified to improve its insulation performance. In this paper, the epoxy/AlN nanocomposites with 1 wt% filler content of AlN nanoparticles were prepared, and the dispersion of nanoparticles was observed. High-energy electron beam was used to treat nanocomposites with the dose of 300, 500, and 700 kGy. The relative permittivity and conductivity of the nanocomposites after irradiation were tested. In addition, the data of surface potential were measured after surface charging for analyzing the dynamic behavior of surface charge and calculating the trap distribution of the nanocomposites with various irradiation doses. The flashover voltage of the nanocomposites influenced by irradiation in LN2 was also analyzed. The results show that irradiation can cause the change of trap distribution and flashover voltage, and the change trend is not monotonous. [ABSTRACT FROM AUTHOR]

Highlights • All the measurement were conducted on an actual well-built GIS/GIL platform. • Quantitative influence of surface charge on the flashover voltage are put forward. • Impacting mechanism of surface charges on flashover voltage is proposed. • The conclusion could provide guidance for the insulation design and fault diagnosis. Abstract Under AC, DC and switching impulse voltages, the surface charges accumulated on the basin insulators of Gas Insulated Substation (GIS) or Gas Insulated Metal Enclosed Transmission Line (GIL) could distort local electric field and even reduce the surface flashover voltage. In order to quantitatively measure the influence of surface charge accumulation on flashover voltage of insulator in actual GIS/GIL apparatus, a high-precision 3D surface charge measurement platform and a reasonable model were established for flashover tests in reference to the insulation design and flashover properties of actual 220 kV GIS basin insulator. The surface charge accumulation dynamics and corresponding flashover voltages of the built models under different conditions were captured and analyzed. The results indicate that, as the density of accumulated surface charges increases under either AC, DC or switching impulse voltage application, the surface flashover voltage would decrease from 62.1 kV to 55.7 kV, namely a margin of 10.3% under AC voltage application. In the context of DC voltage, there appears a 22.8% flashover voltage drop, from 61.0 kV to 47.1 kV. While for the case of switching impulse voltage, the charge accumulation reduced the flashover voltage to 52.9 kV with a 13.6% decline from 61.2 kV. Based on the simulation and theoretical calculations, the 'enhanced electric field zone' was identified to justify the influencing mechanism of surface charges on flashover voltage. The research results could contribute to optimal insulation design and fault diagnosis of basin insulator in GIS/GIL. [ABSTRACT FROM AUTHOR]

In this paper, the effect of surface charges and pollution on flashover voltage of polymeric insulators under DC voltage have been investigated and analyzed. For this purpose, four types of polymeric insulators with different profiles have been selected and then experimental tests of DC flashover voltage have been performed. According to the obtained results, with increasing pollution in presence of positive surface charges flashover voltage reduce, but negative charges increase it. Also in this paper, a model based on geometric parameters including specific leakage distance, shed spacing to shed depth ratio, amount of surface charges and pollution is proposed using an artificial neural network. The comparison of the obtained results from experimental tests and ANN model show that the results of ANN are consistent with experimental tests. [ABSTRACT FROM AUTHOR]

The authors investigated the effect of the insulator hydrophilic fraction on the pollution flashover performance by the up‐and‐down method. The hydrophobicity of parts subjected to a high electric field intensity such as two ends of an insulator, may be weakened by corona discharge. In this study, they simulated the behaviour of composite insulator surfaces at six hydrophilic fractions. Furthermore, arc discharge was recorded using a high‐speed camera and the probability of arc discharge was analysed. They found that as the hydrophilic fraction was increased, the 50% probable flashover voltage first decreased and then increased. The wetting process and discharge type could be classified into two types and the flashover process could be divided into two stages by a clear hydrophilic fraction boundary through leakage current characteristic, discharge probability, and arc shape analysis. The results indicated that uneven hydrophobicity loss might lead to further flashover voltage reduction, up to 26.5% lower, than that with uniform hydrophilicity. This should be considered in transmission line design and maintenance of composite insulators. [ABSTRACT FROM AUTHOR]

Surface modification of polytetrafluoroethylene (PTFE) is performed by nitrogen ion implantation for improving the PTFE surface flashover voltage in vacuum. In this paper, nitrogen ions are produced by an electron cyclotron resonance ion source. The properties of the samples are investigated with X-ray photoelectron spectroscopy, electrometer, microhardness tester, surface potential measurement, and surface flashover system. The Stopping and Range of Ions in Matter software is used to simulate the ion implantation. Experimental results show that the surface flashover voltage of treated samples improves remarkably and increases with the injection energy. After ion implantation, the content of fluorine in the treated samples decreases, and the content of oxygen increases. The surface conductivity increases from $1.15\times 10^{{-15}}$ to 1.36 10−13 S/m, the surface potential decreases faster, and the trap density and energy increase with the implantation energy. The process of electron avalanche and the accumulation of surface charges have been suppressed, thus hindering the development of flashover and improving the surface flashover voltage. [ABSTRACT FROM AUTHOR]

Environmentally friendly DC gas insulated transmission line (GIL) is currently one of the hot topics in advanced electric power equipment. Recently, fluoronitriles have been widely studied and considered to replace SF6 in GILs. In this paper, the breakdown voltage, insulator flashover voltage, and the partial discharge inception voltage of fluoronitriles / CO2 gas mixtures are reported in a DC electric field. The mole ratio of the mixed gases are 4 : 96 % and 8 : 92 %, and the gas pressure is in the range 304.7 to 717.83 kPa. Based on the results, the breakdown field strength of fluoronitriles / CO2 gas mixture shows a growth tendency with increasing gas pressure in a uniform electric field. At 717.83 kPa, the positive breakdown field strength is higher than the negative and reached a maximum. In a non-uniform electric field, the negative breakdown voltage of fluoronitriles / CO2 gas mixture increases with increasing gas pressure. In the contrast, the positive breakdown voltage decreases with the rise of gas pressure, which exhibits a significant polarity effect. The flashover voltage of fluoronitriles / CO2 gas mixture increases with increasing gas pressure. At the same gas pressure, the negative flashover voltage is slightly higher than the positive. The negative flashover voltage of fluoronitriles / CO2 gas mixture at 717.83 kPa is equal to 96.06 % of SF6 gas at 0.5 MPa abs. The negative partial discharge inception voltage (PDIV) of the fluoronitriles / CO2 gas mixture is greater than the positive, and both 4 : 96 % and 8 : 92 % gas mixtures showed higher PDIV than the SF6. Considering the insulation characteristics, the fluoronitriles / CO2 mixture has the potential to replace SF6 in DC gas insulated transmission lines. [ABSTRACT FROM AUTHOR]

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

Polluted insulators at high voltages has acquired considerable importance with the rise of voltage transmission lines. The contamination may lead to flashover voltage. As a result, flashover voltage could lead to service outage and affects negatively the reliability of the power system. This paper presents a dynamic model of ac 50Hz flashover voltages of polluted hydrophobic polymer insulators. The models are constructed using the regression tree method, artificial neural network (ANN), and adaptive neuro -fuzzy (ANFIS). For this purpose, more than 2000 different experimental testing conditions were used to generate a training set. The study of the ac flashover voltages depends on silicone rubber (SiR) percentage content in ethylene propylene diene monomer (EPDM) rubber. Besides, water conductivity (μS/cm), number of droplets on the surface, and volume of water droplet (ml) are considered. The regression tree model is obtained and the performance of the proposed system with other intelligence methods is compared. It can be concluded that the performance of the least squares regression tree model outperforms the other intelligence methods, which gives the proposed model better generalization ability. [ABSTRACT FROM AUTHOR]

The inner area close to cap and pin of insulator is sometimes heavier polluted than the outer area, causing the contamination pattern on insulator surface look like ring-shape. This kind of non-uniform pollution may affect insulator flashover voltage. In this paper, artificial pollution tests of 4 types of porcelain and glass insulators with ring-shaped non-uniform pollution were carried out. Experimental results indicate that the SDD (salt deposit density), the non-uniform pollution degree K (the SDD ratio of inner part to outer part), the heavily polluted area with radius r, and the insulator profile all have significant effects on insulator flashover performance. The effects of K and r on flashover performance can be reflected by the change of pollution layer conductivity during flashover. Under ring-shaped non-uniform pollution, the relationship between Uso and SDD can still be expressed by negative power function, while coefficient a varies obviously with pollution non-uniformity, but exponent n does not. Finally the correction coefficients of flashover voltage considering non-uniform pollution degree K were also calculated for outdoor insulation design. [ABSTRACT FROM AUTHOR]

The study of the surface morphology changes in epoxy resin under direct current power supply in SF6 is of great significance to research into the surface flashover mechanism and the improvement of flashover voltage. In this paper, the epoxy resin was subjected to different degrees of aging in an electric field formed by rod-rod and pin-pin electrodes. Taking the pin-pin electrode as an example, the surface morphology of the same position with different number of flashovers were measured by atomic force microscopy and scanning electron microscopy, and the surface chemical characteristics were explored by Fourier transform infrared spectroscopy and energy dispersion spectrum. Meanwhile, the fractal dimension was introduced to characterize the surface morphology in a quantitative manner: the influence of aging on the flashover voltage was then explored. The research results showed that swelling, cracking, and granular bumps, were three typical surface features, and these were successively formed during aging. As the aging time increased, organic groups on the surface of epoxy resin decreased in number, whilst the inorganic filler mass fraction increased. Moreover, with increasing number of flashovers, the surface morphology gradually changed from disorderly to orderly, from complex to simple, from chaotic to self-similar, when the aging region was changed from the electrode position to the middle of the two electrodes. Furthermore, with prolonged aging, the flashover voltage was reduced to a certain extent. [ABSTRACT FROM AUTHOR]

Poly(styrene-co-divinyl benzene) was irradiated under gamma-rays at various doses up to 25.6 kGy. The samples were analyzed by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) before and after the irradiation, and the flashover voltage of materials under different irradiation dose was measured. Results showed that the surface of material was oxidized after irradiation and the oxygen content was the highest (12.29%) when the irradiation dose was 19.2 kGy. In addition, flashover voltages decreased for irradiated samples as compared with the non-irradiated one (R0), and their flashover voltages values were inversely proportional to the oxygen content. [ABSTRACT FROM AUTHOR]

• Comparative tests of LPSs under the same electro-geometric conditions. • Experimental validation of the lightning-repelling performance of CTSs. • Experimental validation of the improved lightning protection performance of ESE terminals. There are still several uncertainties and conflicts regarding the lightning protection performances of conventional and nonconventional lightning protection systems. Discharge physics and experimental studies reveal the lightning protection systems' performances. However, there are also some studies suffering from commercial concerns. Theoretical efforts and test results are generally valid for specific configurations and are insufficient in generalizations. Another shortcoming of the experimental studies is that the experiments and experimental parameters are limited due to the limited laboratory facilities. This paper presents compact and comparative test results for Franklin Rods (FRs), charge transfer systems (CTSs), and early streamer emission (ESE) rods. For this purpose, the flashover voltage tests and lightning attachment rates of the mentioned protection systems are determined using switching impulses under the same electro-geometric conditions. Experimental results showed that FR and ESE terminals had similar flashover voltage and lightning attachment characteristics. CTSs could have performed better in diverting the lightning strikes when used alone. Therefore, there is a need for additional tests and field data to validate the claimed better lightning prevention performance of CTS systems and the lightning attachment performance of ESE terminals. [ABSTRACT FROM AUTHOR]

In this paper, an atmospheric-pressure dielectric barrier discharge is used to modify the surface of the epoxy material and enhance the dissipation of surface charge to reduce the accumulation of surface charge. In the experiments, atmospheric-pressure air dielectric barrier discharge is driven by a microsecond pulse generator. Surface properties of epoxy before and after the plasma treatment are characterized by water contact angle, surface potential, and surface/volume conductivity measurements. Atomic force microscope and X-ray photoelectron spectroscopy are used to investigate the changes of the morphology and the chemical composition of the epoxy surface. Experimental results indicate that the surface of epoxy is etched by the plasma and the increase of the surface roughness enhances the surface insulation ability. The O radicals in plasma and the carbonyl groups formed on the surface make the surface charge trap shallower, change the epoxy surface composition then increase the surface conductivity and accelerate surface charge dissipation. When the epoxy is treated for an appropriate time, the epoxy surface insulation performance will be enhanced obviously and the surface charge dissipation will be accelerated. [ABSTRACT FROM PUBLISHER]

EHV and UHV high voltage transmission lines frequently pass through high vegetation areas as well as national forests where there is a significant risk of wildfire by natural or manmade causes. Firefighters use aerial vehicles to douse fires by dumping large amount of fire retardant liquid that is conductive, thus increasing the risk of insulator flashover and power interruptions. In this paper, an ammonium polyphosphate based fire retardant liquid was evaluated to understand its effect on insulator flashover properties. Composite and ceramic insulators, suitable for 115 kV transmission lines, were studied by the solid layer test method. Tests were conducted with and without external wetting by fog. Results indicate that there is a high probability of flashover if the entire insulator is coated with the fire retardant liquid. Statistical methods were applied to extend the validity of testing results to predict flashover voltages at higher voltage levels of 230, 345 and 500 kV. It is shown that standard insulator dimensions used for EHV and UHV lines in fire prone areas could be deficient and additional insulation required to improve the flashover performance to acceptable levels in such locations has been determined. [ABSTRACT FROM PUBLISHER]

This paper presents a study on the electrical performance of ceramic (ANSI 52-1, ANSI 55-2) and polymeric (ANSI DS-15) insulators used in medium voltage electrical systems (between 7kV y 35 kV) when fungi growth of Phanerochaete chrysosporium and Penicillium Sp. on their surface is presented. Biological contamination of electrical insulators is a problem that has been reported in tropical areas in Europe, Asia and Oceania and it may reduce the reliability of electric power systems. The biocontamination was conducted in Bogota, Colombia for 50 consecutive days (for each microorganism) using a chamber that controls light, moisture and temperature. Laboratory tests of flashover voltages and leakage currents were performed. After fungus biocontamination reductions in flashover voltages about 21% and 8% were reported for ceramic and polymeric insulators, respectively. In all cases, the leakage currents increased by 20% or higher. [ABSTRACT FROM AUTHOR]

Ice flashover threatens the security and reliability of power transmission. However, the ice flashover mechanism of insulators remains poorly understood. This study analyses water droplet freezing and ion distribution in ice layer under alternating electric field. It also investigates ion migration during icing process of insulator string under alternating electric field and its effects on insulator flashover. Results showed that the average freezing time of water droplets was related to electric field strength. The extent of ion migration during freezing decreased with increasing electric field strength. The maximal melting water conductivity of the ice layer and icicle of the insulator formed under energized condition was higher than the corresponding freezing water conductivity but lower than that under non-energized condition. Furthermore, the hanging location of each insulator significantly affected the melting water conductivity of the ice layer. The surface conductivity of the ice layer increased because of the conductive ion migration in freezing water during freezing, which was an important factor that decreased the flashover voltage of the ice-covered insulator. The existence of alternating electric field would impact the extent of ion migration. This study may serve as a reference for updating prediction flashover model of ice-covered insulators during the melting period. [ABSTRACT FROM AUTHOR]

Ethylene-vinyl acetate (EVA) composite is widely used in cable accessories to uniform electric field and prevent partial discharge. However, local electric field distortion will cause charges accumulation and flashover, which is susceptible to the tensile strain upon the materials. Carbon Black (CB) nanoparticles can be applied to adjust the electrical properties of polymer composite. The effects of the CB contents on the surface charge and flashover characteristics of EVA/CB nanocomposite under various tensile strains need further investigation. In this paper, samples were prepared by incorporating CB nanoparticles into EVA matrix with fraction of 0, 1, and 5 wt% respectively. Tensile strains of 5, 10 and 15 % were applied to provide three deformations, which were compared with the unstretched sample. The dependence of the relative permittivity, surface charge decay and flashover characteristics on the CB contents under various tensile strains were measured. The trap distribution and carrier mobility were calculated to analyze the tensile strain dependent surface flashover. Obtained results show that the surface flashover voltage decreases with the increasing tensile strains for all the samples. Moreover, the flashover voltage of the samples doping with 1 wt% CB nanoparticles is higher than the other samples. The combination effects of trap distribution and carrier mobility are responsible for the above results. The surface flashover is more prone to occurrence under higher tensile strain, which should draw enough concern for the security of power cable operation. [ABSTRACT FROM AUTHOR]

Affected by long‐term crosswind, insulator surface will get coated with fan‐shaped non‐uniform pollution, which lowers insulator flashover voltage as previous study revealed. In this study, a further research in specific to HVDC line insulation is presented. Taking typical dc insulator as the sample, its dc flashover performance under fan‐shaped non‐uniform pollution was tested. Then the influence of that kind non‐uniformity was investigated through analysing the pollution layer residual resistance, the flashover process and critical flashover voltage. Finally the relevant HVDC insulation selection was made. Research results indicate that: under fan‐shaped non‐uniform pollution, insulator flashover voltage (U50) gets impaired, and is more obviously impaired by ratio J of windward to leeward side salt deposit density (SDD) than leeward side area proportion T; under various T and J, there is still an exponential relationship between U50 and SDD; under fan‐shaped non‐uniform pollution the pollution layer residual resistance decreases, which theoretically promotes the arc propagation and flashover process, and thus finally lowers flashover voltage; for the transmission line in area with fan‐shaped non‐uniform pollution, adding insulator units to strengthen the withstand property are needed. [ABSTRACT FROM AUTHOR]

The occurrence of large‐scale haze–fog weather in some developing countries brings a new threat to the safe operation of outdoor insulation. In order to study the effect of the haze–fog on the flashover performance of insulators and the flashover mechanism, kieselguhr, calcium sulphate (CaSO-4) and ammonium sulphate ((NH4)2SO4) in different particle sizes were mixed with ultrasonic fog to simulate the haze–fog environment and quantitative ac flashover experiments on the standard suspension porcelain insulator were carried out. The test results indicate that the flashover voltage is related with the pollution degree, particle component, particle size and fog‐water conductivity, and may decrease by more than 20% under haze–fog environment. The effect of salt aerosols on flashover voltage is determined by the solubility and larger than that of non‐soluble mineral aerosols or organic carbon aerosols. The flashover voltage increases with the increase of the particle size, but decreases with the increase of fog‐water conductivity. The flashover of insulator under haze–fog condition is a special kind of pollution flashover in essence. [ABSTRACT FROM AUTHOR]

This paper is aimed at the study of the propagation of discharge at the surface of solid insulator and the development of an analytical model of flashover in air. The experimental results show that the critical conditions of flashover are met when the discharge reaches the half of creeping distance. Using electrical equivalent circuit and the impedance criterion, we developed a relationship giving the flashover voltage (FOV). This formula evidences the fact that flashover voltage depends on the discharge temperature, the capacitance and the resistance of solid insulator, and the propagation conditions of the discharge. We also show that the computed FOV are in a good accordance with the experimental data. [ABSTRACT FROM AUTHOR]

This paper presents a self-consistent multi-arcs dynamic model for high voltage polluted insulator under impulse voltage. This model is an improvement of that one developed for single arc; it is based on an electrical equivalent circuit consisting of a series of different partial arcs and residual layer resistance. It takes into account the configuration of insulator, applied voltage polarity and the instantaneous changes of discharges parameters. The proposed model enables to compute the flashover voltage and leakage current and to show the influence of dry bands on the voltage distribution along the surface and furthermore on the electrical performance of polluted insulator. It is validated using a simple plane model in the case of uniform and non-uniform polluted bands. The computed flashover voltage and leakage current are found in good agreement with those measured experimentally. [ABSTRACT FROM AUTHOR]

The flashover performance of insulators is significantly affected by the degrees and ways of wetting the pollution layer. However, there have only been a few reports on the wetting condition and its effects on the flashover characteristics of pollution on insulators to date. In this paper, a phase-angle difference-based method is proposed to test the wetting conditions of the pollution layer on insulators. A corresponding measuring device is also developed. The wetting process of the pollution layer on aerodynamic-type glass insulators is studied in an artificial climate chamber using the developed device. The related flashover performance is studied via the even-rising voltage method. Test results show that the phase-angle difference (PAD) curve accurately reflects the entire wetting process of the pollution layer from the initial stage, through the saturated stage to the oversaturated and washing away stages. Over the wetting process, the PAD curve initially drops sharply, and then remains stable for a few minutes before eventually rising slowly to the initial value. The PAD curve has its lowest value when the pollution layer is wetted to saturation, which occurs after approximately 5 min in our experiments. The flashover voltage characteristics of insulators are also significantly affected by the wetting conditions of the pollution layer. The flashover voltage in the saturated stage is shown to be lower than that in the other stages. Therefore, to improve the accuracy of the artificial pollution tests, quantitative methods (including PAD) should be used to obtain the exact time of wetting to saturation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A nanosecond pulsed Ar/OMCTS plasma system is developed for epoxy resin fabrication. • Multiple properties of EP are improved simultaneously by regulating OMCTS contents. • Formation of shallow traps contributes to the increment of surface conductivity. • Quantum chemical simulations verify the mechanism of improved electrical insulation. Epoxy resin (EP) is one of the most widely-used insulating support materials in electrical power systems, with its insulating performance playing an important role in high-voltage engineering. In this study, a nanosecond pulse-driven Ar/Octamethylcyclotetrasiloxane (OMCTS) plasma jet is developed for fabricating nanocomposite dielectric materials to enhance their EP properties. It is demonstrated that the plasma-enabled polymerization effectively modifies the physical morphology and chemical composition of EP surfaces, where the surface roughness greatly increases with the deposition of less-polar silicon-containing films. Moreover, with an increased OMCTS carrier gas flow rate, the surface conductivity of the EP increases by two orders of magnitude, which is directly related to the appearance of shallow traps in the dielectric surface after Ar/OMCTS plasma treatment. Results show that the trap depth of the electron decreases from 1.21 to 0.99 eV post-treatment, with the OMCTS fragments becoming shallow trap points for charge detrapping and transportation processes. Moreover, the addition of a controlled amount of OMCTS increases the plasma discharge intensity, promotes silicon film deposition, and thus significantly improves the insulation and wettability performance, with higher flashover voltages and water contact angles (WCA). By contrast, excessive addition of OMCTS inhibits the plasma discharge due to the absorption and consumption of energetic electrons by OMCTS molecules. Quantum chemistry calculations are further developed to explore the mechanisms of plasma-induced surface modifications. Overall, the proposed plasma polymerization strategy offers a promising fabrication technique and provides guiding insights into the fabrication of nanocomposite dielectric materials in electrical engineering. [ABSTRACT FROM AUTHOR]

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

Previous simulation and observations showed that, the air flow field at windward and leeward side of insulator string will probably be different if the wind velocity is over a certain value, and thus causing the imparity of contamination degree at the two sides. In this paper, fan-shaped non-uniform polluting method was used to artificially simulate the different pollution severity at windward and leeward side of insulator string. Then, the effects of fan-shaped non-uniform pollution on ac flashover performance of 5 types of insulators were discussed. Test results indicate that, SDD, the ratio SDD of windward to leeward side (W/L), the occupation ratio of leeward side (k), will affect the ac flashover performance of insulator string. U50 and SDD still can be expressed by the negative power function. A reduction in W/L from 1/1 to 1/15 would give a decrease about 23% in a value, which causes U50 reducing about 25%, but n value changes little. The correction method proposed by EPRI is also applicable for fan-shaped non-uniform pollution, but has difference. A larger creepage distance of insulator does not mean that the creepage distance utilization rate is higher. Due to the influence of fan-shaped non-uniform pollution, the existing insulation configuration of transmission lines in heavily polluted areas may not satisfy the required insulation margin. The results have certain reference significance for the design and selection of transmission line external insulation. [ABSTRACT FROM AUTHOR]

DC transmission helps to solve the decentralization of distributed wind power generation and other renewable power sources to enhance system performance. But the existence of surface charges by the corona makes earlier insulation failure and plays an important role during the development of the surface flashover. The influences of the ambient temperature and the polarity reversal voltage on the surface charge and the flashover of the heat-shrinkable polymer are not completely clear. In this paper, the carrier mobility and the volume conductivity were employed to explain the temperature dependent surface charge decay results. The initial surface charge density and decay rates served for analyzing the effects of polarity reversal voltage. Furthermore, the flashover experiments of the samples charged by the polarity reversal voltage at different ambient temperatures were conducted. Obtained results show that the descending speed of the surface charge becomes faster at higher temperature. An obvious temperature dependence of the carrier mobility and the volume conductivity is observed. Moreover, the surface charges of the samples charged by the voltage with shorter reversal time decay more rapidly. The flashover voltage increases with the increasing ambient temperature because of less accumulated surface charges in this condition. Considering the accelerated surface charge decay by the increasing temperature and easier charge accumulation during the steady negative period, attentions should be paid to the design of DC insulation and the security of operation. [ABSTRACT FROM AUTHOR]

Super-hydrophobic coatings have recently drawn a lot of attention in research and applications towards reduction of ice accumulation on insulators. This paper presents a new type of hybrid coating fabricated via self-assembly of a super-hydrophobic layer on a semi-conducting layer. Hydroxy-terminated polydimethylsiloxane (OH-PDMS) modified nano-silica is used for fabrication of the super-hydrophobic layer. Fabrication procedures, hydrophobic characteristics, and flashover performances of the hybrid coating are presented. Experimental results show that the hybrid coating has a dual micro- and nano-scale hierarchical structure and a water contact angle greater than 155°. Surface resistivity, volume resistivity, temperature rise, and surface flashover voltages of the hybrid coating are also presented. Temperature distribution on the hybrid coating is simulated for further analysis. The results show that the hybrid coating is capable of improving the electrical field and surface temperature along the surface of the coating. [ABSTRACT FROM AUTHOR]