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Ceramic insulators on High Voltage Overhead Lines (SUTT) in Indonesia, particularly on the Payakumbuh-Koto Panjang transmission line, are often exposed to natural contamination. This research evaluated the impact of natural contamination on the Total Harmonic Distortion (THD) of leakage current in 150 kV insulators, representing a new approach to understanding insulator performance in contaminated environments. Tests were conducted at the High Voltage Laboratory at Universitas Gadjah Mada using various types of contamination: moss, dust, flashover marks, and clean insulator conditions. The results showed that insulators contaminated with moss exhibited a maximum leakage current of 0.306 mA, with the highest THD reaching 36%, while insulators in clean condition had an average THD of 32.5%. Insulators contaminated with moss, dust, and flashover marks showed THD values of 25.37%, 19.03%, and 28.71%, respectively. Moss and flashover can significantly increase THD, especially when the number of disc-type insulators increases. These findings underscored the importance of a more intensive and targeted maintenance strategy for insulators to minimize the negative impacts of natural contamination, particularly in mountainous areas. This approach contributes to the enhancement of the reliability of high-voltage transmission lines in Indonesia. [ABSTRACT FROM AUTHOR]

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Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Operation accidents caused by deteriorated insulators occur from time to time, which poses a direct threat to the safe and stable operation of transmission lines. Much research has been done at home and abroad on the degradation mechanism of deteriorated insulators, the electric field distribution characteristics of insulator strings and the influence of deteriorated insulators on the space electric field, but there is little research on the influence of three-phase electrification on the space electric field of insulator strings. Therefore, this paper studies the simulation and detection of electric field distribution of deteriorated insulators in three-phase transmission lines. First, the difference between three-phase electrification and single-phase electrification on the space electric field of insulator strings is simulated and analyzed, and the influence of deteriorated insulators on the space electric field distribution of insulator strings under three-phase electrification is studied. Second, based on simulation results, a detection method for deteriorated insulators in three-phase overhead trans-mission lines is proposed, and a non-contact space electric field measurement device based on Unmanned Aerial Vehicle (UAV) is developed. Finally, a Unmanned Aerial Vehicle inspection system is used to test the transmission lines in combination with an electric power department, and the simulation results and the effectiveness of the proposed detection method are verified. Results show the electric field distribution of insulator strings is obviously different between three-phase electrification and single-phase electrification, and when the detection distance is 300 mm, the proposed detection method and device can effectively identify deteriorated insulators in three-phase transmission lines. [ABSTRACT FROM AUTHOR]

Flashover at gas/insulator interface acts as a vital challenge to the safe and stable operation of gas-insulated system especially when involved with surface metallic particle. In this paper, flashover characteristics at SF6/epoxy insulator interface were investigated concerning on the tracking property based on image analysis. DC flashover experiments were operated for basin-type spacer with metallic particle at various locations. Flashover voltage was obtained and tracking on the surface after successive flashover was captured. Improved image analysis method based on fractal theory was carried out to evaluate tracking pattern quantitatively. The relation between the fractal dimension of tracking and field distribution at particle tip was revealed. Obtained results showed that flashover voltage decreased due to severe field distortion with moving particle from ground to HV electrode. Meanwhile, fractal dimension of tracking covering the area from particle to ground electrode indicated centralized tendency. Simulation result confirmed this variation as the consequence of centralized field distribution at the tip of particle. The quantitative relation between fractal dimension and field distribution suggests new sight to estimate the influence of metallic particle on insulation property in the gas-insulated system.

In present decade, amidst all the remarkable equipment belonging to the power systems—the insulator stands out to be all-important because of their crucial role in power generation and transmission networks. Despite the above fact, they also transpire to have many constraints with respect to their normal function and longevity. Reports states that insulators are the weakest link due to their instant breakdown nature and other facts. Among all those notable facts, breakdown due to surface contamination of the insulators emerges to be intriguing for the present research world. Researchers present countless techniques to eliminate the same. Out of all the techniques, superhydrophobic coating stands out to be noteworthy for their resistance against moisture, wetting, ice and dust. Also, this coating outperforms the conventional RTV (Room Temperature Vulcanizing) silicone rubber coating with respect to delayed flashover occurrence. That is the time required for flashover occurrence is delayed in superhydrophobic coating. This novel attribute of superhydrophobic coating requires an experimental analysis. Hence, the proposed work serves this objective by preparing a superhydrophobic solution with PDMS (Polydimethylsiloxane) chemical. Results show that the contact angle and sliding angle of the water droplet dropped on this coating are above 170° and 5°, respectively. Simulation model for studying flashover occurrence, adhesion property of water was built using COMSOL Multiphysics Software. [ABSTRACT FROM AUTHOR]

Insulator pollution flashover has a high probability in the faults of transmission and distribution system. Due to its complex formation process and various influencing factors, the relevant studies are mostly based on experimental tests and empirical formulas, which do not fully consider the impact of random factors on the flashover process. The quantifiable algorithms are lacking, and it is difficult to effectively predict pollution flashover. In this article, the quantum transition theory is introduced in the streamer theory to calculate the energy-level transition probability of the particle on the surface of polluted insulator. The randomness of particle collision cross section is considered, and the initial discharge voltage is calculated by probability theory. The effects of active particle content, ambient temperature, and relative humidity on the initial charge number of insulator pollution flashover are analyzed. On this basis, the initial discharge process of insulator pollution flashover is studied. The experimental results show that the calculated results of insulator pollution flashover initial discharge voltage based on quantum energy-level transition probability are consistent with the experimental values, which has engineering application value for insulator pollution flashover prediction. [ABSTRACT FROM AUTHOR]

SF6/CF4 mixture is considered a potential substitution for SF6 in gas-insulated equipment owing to the considerable insulation and low temperature characteristics of CF4. This paper concerns the substitutability of the mixture on the surface flashover property. Epoxy resin composites for solid insulators are applied since flashover at the insulator interface often occurs and results in severe damage to the safe operation of the equipment. Two kinds of electrode systems are designed to study DC flashover properties with different electric field uniformities. The obtained result shows that the flashover voltage in the 20% SF6/80% CF4 mixture achieved more than 70% of the voltage in SF6 at the same pressure. The mixture shows considerable synergy in the surface flashover process and performed different tendencies with varying gas pressures and contents under different electrode systems due to the influence of surface accumulated charge. Moreover, it is considered that surface charge due to ionization may result in a reversal phenomenon for voltage polarity with increasing pressure. The results indicate the possibility of SF6/CF4 functioning as an efficient substitution of SF6 with a considerable insulation property and improved environmental protection characteristics. [ABSTRACT FROM AUTHOR]

This paper introduces an analytical model of contaminated insulators under critical conditions. The dynamic mathematical model based on the description of the equivalent electrical circuit approach and the criterion for the propagation of discharge has been improved. A few laboratory tests were conducted on practical insulators installed to measure the flashover voltage and determine dynamic arc parameters (A and n). The electric arc constant values are extracted based on the simulation of the experimental results using the genetic algorithm technique with several levels of pollution. The critical parameters, which are the current, length, and resistance of discharge, have been measured and calculated based on the proposed model. The actual results of the proposed models' voltage were compared with the experimental results and previous research study under various resistance of pollution layers. Statistical analysis based on different coefficients were applied to validate the reliability of the proposed models. The experimental and simulation findings show the insulator's expected performance under various operating conditions per the IEC 5070 Standard. [ABSTRACT FROM AUTHOR]

The surface voltage of an insulator assumes importance for understanding tracking and flashover characteristics. Until now, determination of surface voltage of insulating surfaces is left to simulation software and such simulations are left unverified experimentally, leading to uncertainty of the results, which may sometimes be erratic with improper choice of boundary or initial conditions or inaccurate material properties, nonlinearities etc. The paper presents a novel method, using which the surface voltage of any insulating surface such as insulator strings or transformer bushings can be measured. Unlike a conducting surface, the measurement of insulating surface voltage using voltage dividers would be erratic as the measuring arrangement itself will vary the voltage division due to the local unknown impedance between the insulated surface and hv conductor. Recently a method for measurement of surface voltage of an insulated conductor using cylindrical strips was reported. In this paper, based on analytical derivations, a more generalized method of measurement, applicable to any point on an insulating surface of arbitrary geometry is proposed using circular-disc strips. The proposed experimental method is applied to insulator strings and transformer bushings and validated by simulation of the entire systems. The simulation and experimental results are in excellent agreement. [ABSTRACT FROM AUTHOR]

Insulator pollution flashover occurs frequently and is harmful to the power transmission and distribution network. But the randomness of the pollution flashover and the complex influencing factors make it difficult to be predicted. The objective of this paper is to study the mechanism of the discharging on insulator surfaces and design a the calculation method which derives flashover probability. By calculating the distorted electric field in the initial streamer discharge quantitatively and combining it with the equivalent circuit of the insulator surface, the initial discharge voltage is derived. By analyzing the change in power input and dissipation in the process of the arc discharge, we propose the criterion on arc development and extinction, and the critical flashover conductivity of the insulator is obtained. Based on the probability density function, the behavior of the factors on the critical flashover conductivity is described, and the probability of insulator pollution flashover is calculated under different environmental conditions. In the validation experiment, the measured initial discharge voltage and pollution flashover ratio are close to the calculated values. The methods proposed in this paper could be used in the quantitative calculation of the initial discharge voltage and the prevention of the pollution flashover on insulators. [ABSTRACT FROM AUTHOR]

This paper aims to assess the effect of dry band location of contaminated porcelain insulators under various flashover voltages due to humidity. Four locations of dry bands are proposed to be tested under different severity of contamination artificially produce using salt deposit density (SDD) sprayed on an insulator. Laboratory tests of polluted insulators under proposed scenarios have been conducted. The flashover voltage of clean insulators has been identified as a reference value to analyze the effect of contamination distribution and its severity. The dry band dimension has been taken into consideration in experimental tests. The flashover voltage has been predicted using an artificial neural network (ANN) technique based on the laboratory test data. The ANN approach is constructed with five input data (geometry the insulator and parameters of contamination) and flashover voltage as the output of the model. Results indicated that the pollution distribution based on the proposed scenario has a significant influence on the flashover voltage performances. Validation of the ANN model reveals that the relative error values between the experimental results and the prediction appeared to be within 5%. This indicates the significant efficiency of the ANN technique in predicting the flashover voltage insulator under test. [ABSTRACT FROM AUTHOR]

• This study innovatively explores the impact of insulator ribs on arc paths, addressing challenges associated with pollution flashovers and arc bridges. • The research introduces flashover voltage gradients and creepage distances as metrics, providing a systematic evaluation of insulator performance and practical design guidance. • Practical recommendations for rib configurations, emphasizing specific ratios and alternating ribs, contribute valuable insights to prevent arc bridging and enhance insulator efficiency. Disc insulators serve as the primary insulating and supporting components in transmission lines. Pollution flashover incidents pose challenges for power practitioners. The disc insulator's ribs can improve the flashover voltage. However, pollution flashover are more likely to occur when there are arc bridges between insulator ribs. This study aims to investigate the impact of insulator ribs on the development path of arcs and flashover performance. The experimental circuit for flashover is constructed to analyze the arc's behaviour and evaluate the insulation performance. Utilizing flashover voltage gradients and creepage distances to evaluate the effectiveness of insulator structures. The insulator forms an arch hinge when two adjacent ribs are close in length, and the uneven air pressure within the arch hinge creates a thrust that causes the arc to break away from the surface and form a bridge. Maintaining a rib spacing to rib length ratio between 0.83 and 1.5 is recommended to prevent arc bridging. Alternating ribs improve creepage distance utilization, enhancing insulation with a recommended rib spacing to rib length ratio between 0.67 and 1.5. Avoiding low or high coefficient values is crucial to prevent arc bridging or inefficient insulator space use. The spacing between the insulator connector and the nearest rib should be more than the length of the rib, otherwise there is an increased likelihood of direct arcing connector the upper and lower umbrella skirts The spacing between the insulator connector and the nearest rib should exceed the rib length and the nearest rib to minimize the risk of direct arcing between the upper and lower umbrella skirts. The research content can provide a theoretical and experimental basis for improving the insulator structure and increasing its flashover voltage. [ABSTRACT FROM AUTHOR]

Electric field optimization is a critical technique to ensure the compact structure and reliable operation for AC gas insulated power apparatus. To obtain a more uniform electric field distribution, this paper proposes the concept of the d-SFGM insulator, i.e., applying the surface functionally graded material (SFGM) with a designed thickness (d) distribution of high permittivity along the insulator surface. The magnetron sputtering technique was used to fabricate the d-uniform insulator and the d-SFGM insulator by depositing BaTiO3 layers. The theoretical analysis indicates that the electric field distribution is optimized using the d-SFGM insulator, followed by the d-uniform insulator. The finite element simulations were employed to investigate the electric field distributions and dielectric losses of different insulators. The results show that for the case of the d-uniform insulator, a higher permittivity or larger thickness of the sputtering layer results in a more uniform electric field distribution. With the application of the d-SFGM insulator, the maximum electric field strength and dielectric loss are both significantly reduced compared to the d-uniform insulator. Finally, experimental tests were conducted to further verify the feasibility of SFGM. The AC flashover voltage of the d-SFGM insulator is much higher than those of the conventional insulator and the d-uniform insulators. Therefore, the d-SFGM insulator has great potential for improving the reliability of the AC gas insulated power apparatus.

High Voltage Direct Current (HVDC) systems are increasingly being adopted around the world to integrate renewable resources, increase power transfer, and allow flexible grid operation. HVDC overhead lines play a critical role in this, and focus is needed on the research of composite outdoor insulators failure. In the case of a pole to ground fault of a bipolar scheme, the healthy pole experiences a slow transient overvoltage similar to a Switching Impulse (SI) superimposed on the operational DC voltage. However, there is no standard test for such voltage superimposition. This paper investigates the performance of a composite insulator stressed with such superimposition under dry and rain conditions. To determine the direct voltage influence on the flashover voltage, the results have been compared with the SI only case. Four different rain conductivities have been used in the test program because these insulators can be exposed to different acid conductive rain types, typical of industrialized environments. Both vertical and horizontal orientations have been studied. It was possible to conclude that, in most cases, the direct voltage pre-energization has a negative impact on the flashover performance. The increase in rain conductivity leads to lower flashover values, and the horizontal orientation outperforms the vertical configuration. Under these test conditions, the flashover voltages were all larger than a typical DC operational switching surge. Thus, in the case of pole to ground fault, the healthy pole failure risk appears to be low. However, further research is needed on higher voltages and polluted conditions. [ABSTRACT FROM AUTHOR]

The demand for DC gas-insulated switchgear/gas-insulated transmission line (GIS/GIL) becomes more and more urgent in recent years owing to the rapid development of high voltage direct current (HVDC) transmission systems. Insulators in DC GIS/GIL could easily accumulate a large number of charges on its surface during long-term operation, which might lead to overstressing of polymeric insulation or surface flashover. Therefore, it is of great significance to propose an effective method for dissipating extra surface charges. However, achieving charge dissipation without opening the tank is still a great challenge to SFC6-insulated equipment for a long time. In this paper, a novel method, which is named X-ray based non-contact charge dissipation method (XNCDM) for insulators in SF6-insulated equipment, is proposed. The effects of X-ray irradiation on the charges dissipation and the influences of irradiation dose were experimentally investigated in SF6. The mechanisms underlying are discussed in detail. Results show that surface charges on the insulator can be almost completely dissipated after short-time X-ray irradiation with enough dose, owing to the significant enhancement of electric conduction along the insulator surface and charge neutralization by gas ions near the gas-solid interface. This paper provides a novel technique for realizing rapid surface charge dissipation on the insulator, which is of great significance for a variety of engineering applications of DC GIS/GIL. [ABSTRACT FROM AUTHOR]

Flashovers seriously affect the safe operation of high-voltage transmission lines. The influence of different pollutants on the flashover of insulators differs greatly. For hygroscopic aluminum phosphate, glucose, and other contaminants, the saturated moisture and flashover characteristics can cause flashovers at low humidity. Therefore, it is of great significance to quickly detect the moisture content in the field. In this article, based on the laser-induced breakdown spectroscopy (LIBS) method, the spectral characteristics of aluminum phosphate contamination were studied, and the spectral lines that characterize the content of aluminum phosphate were obtained. The detection limit for phosphorus was calculated according to the calibration curve. The difference in the moisture content of aluminum phosphate contamination also affects the LIBS signal. The atomic spectrum of phosphorus is selected as the analytical spectral lines. Within a certain relative humidity range, spectral data normalization reduces the influence of the moisture content on the mass fraction of aluminum phosphate samples detected by LIBS. The research results are of great significance for the rapid detection of special contamination, such as aluminum phosphate, in actual lines. [ABSTRACT FROM AUTHOR]

In this paper, the influence of surface charges is quantitatively analyzed based on the study of surface charge distribution under DC voltage and flashover characteristics of insulators under superimposed voltage of DC and lightning impulse. It is found that when DC and impulse voltage are in the same polarity, surface charges weaken the electric field along the insulator surface and flashover voltages under superimposed voltage increases. When DC and impulse are in the opposite polarity, surface charges enhance the electric field along the insulator surface, and flashover voltages will decrease. The calculation results of the electric field along the flashover path show that the changing rate of the maximum field strength is approximately equal to the changing rate of flashover voltage, which proves that the influence of surface charges on flashover characteristics of insulators mainly depends on their distortion of the electric field. [ABSTRACT FROM AUTHOR]

Successive flashover would result in carbonized tracking on insulator surface and cause deterioration to the insulation. Thus, investigation of the tracking can be beneficial in understanding flashover characteristics during long-term operation. In this paper, DC flashover was operated on the insulator, and the image of tracking after successive discharge were captured. Improved differential box-counting method (IDBM) was applied to analyze these images based on fractal theory. Weighted item was suggested during the counting procedure for rectangle image with margin covered by cut-size box. Fractal dimension of the tracking was calculated according to the suggested method. It is claimed that the suggested method could estimate the discharge propagation property and deterioration characteristics on the insulator surface. Moreover, IDBM showed advantages in image pre-processing and deterioration property revealed compared to traditional box-counting method attributing to the consideration of color depth. This image analysis method shows universality in dealing with tracking image and could provide additional information to flashover voltage. This paper suggested a potential approach for the investigation of discharge mechanism and corresponding deterioration in future research.

For many years Eskom has followed international guidelines in selecting transmission and distribution insulator products for use in polluted environments. [ABSTRACT FROM AUTHOR]

This paper reports on an investigation into the surface flashover of an insulator in a C4F7N/CO2 mixture which is used as an alternative to SF6. To date, no studies on this aspect have been reported in the literature. This study was done for a uniform field using a 220 kV AC experimental platform. The influence of molar fraction, gas pressure and creepage distance is reported and compared to that in SF6. The results show that small quantities of C4F7N mixed in CO2 can increase the surface flashover voltage but, as the fraction of C4F7N increases, saturation of the surface flashover occurs. The relative surface flashover voltage of 13.0% C4F7N/87.0% CO2 is approximately 80% that of SF6. The empirical formulae on the critical flashover electrical field has been obtained, which may be referenced in the design of environment friendly high voltage equipment. [ABSTRACT FROM AUTHOR]

The flashover of pollution, observed on the insulators used in high voltage transmission, is one of the most important power transmission stakes. It is a very complex problem due to several factors including the modelling difficulties of complex shapes of insulators, different pollution densities at different regions, non-homogeneous pollution distribution on the insulator surface and unknown effect of humidity on the pollution. In the literature, some static and dynamic models have been developed by making some assumptions and omissions to predict the flashover voltages of polluted insulators. This paper aims to experimentally analyse the flashover process and simulation of the distributions of the potential and the electric field under 50 Hz applied voltage on a real model simulating the 175CTV outdoor insulators largely used by the Algerian Company of Electricity and Gas (SONELGAZ). This real model is studied under non-polluted (distilled water), and polluted (distilled water and sand) environments. The simulations were carried out by using the COMSOL multiphysics software. This program uses the finite element method to solve the partial differential equations that describe the field. Experimental results made in the laboratory and simulation results are original and found to be congruent. [ABSTRACT FROM AUTHOR]

The porcelain ceramic insulators have been used for outdoor insulation applications for a long time due to their impressive electrical and mechanical properties. The lightning impulse withstand voltage and flashover voltage characteristics of the insulators are important for insulation coordination of transmission lines and substations. This study presents a computer‐based simulation methodology to determine the positive polarity lighting impulse flashover voltage of porcelain suspension and station post‐insulators. The flashover voltage is determined by evaluating the streamer inception, propagation and sustenance criteria along the suitable paths based on finite‐element‐method‐based electric field computation. The streamer propagation path is found through air along the dry arcing distance rather than along the creepage path of the insulator. The lightning impulse flashover voltage of suspension and post‐insulators are computed based on simulation. The comparison of computed results with the experimental results gives a good agreement between them. [ABSTRACT FROM AUTHOR]

The non-uniform electric field (E-field) distribution is typically considered a key factor in triggering surface flashover inside gas insulated lines (GILs). To improve the E-field distribution along GIL insulators, this study proposes the concept of an interfacial E-field self-regulating (IER) insulator. The capability of the IER insulator with a resistivity-nonlinear (ρ-nonlinear) skin layer to regulate the E-field distribution is validated via theoretical analysis. In this paper, cone-type insulators are coated with epoxy (EP)/SiC composites to fabricate EP/SiC coated IER insulators. Next, an electrical simulation model is built to calculate the E-field distributions and energy losses of the insulators. As the coating thickness or SiC content increases, the E-field regulation function of the EP/SiC coated insulator becomes increasingly significant with increasing leakage current and energy loss. Under DC voltage, nearly 24 hours is required for the E-field distribution along the conventional insulator to reach the steady state. When the SiC content in the coating layer is increased, the transient time of the EP/SiC coated insulators decreases because of the reduced volume resistivity. Furthermore, coating thickness measurements and DC flashover tests are conducted. The coating thickness of the EP/SiC coated insulator is found to increase with increases in the SiC content because of the higher viscosity of the liquid-state coating. The DC flashover voltage of the EP/SiC coated insulator is found to be higher than that of the conventional insulator, with the flashover voltage increasing with the SiC content in the coating layer. [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 breakdown rule of coated inorganic insulators under impulse is illustrated. • Flashover processes under steep-front impulses are recorded. • The breakdown mechanism under steep-front impulse is demonstrated. • Optimization approaches for coating insulators are proposed. Insulators play the vital role in the power transmission, including traditional porcelain/glass insulator and silicone rubber based polymeric insulator. By coating the glass/porcelain insulators with silicone rubber, the advantages of organic and inorganic dielectrics are integrated. However, it was found that the breakdown probability of coated insulators under steep-front impulse increases significantly. It suggests the possible degradation of insulator material and might become the hidden danger of power system. Therefore, in this research, a great deal of steep-front impulse voltage tests are carried out over various types of insulators. It demonstrates that the performance degradation is introduced by RTV coating instead of intrinsic defects. Then, based on the analysis of flashover paths and breakdown locations, the breakdown mechanism of coated insulator under steep-front impulse is illustrated. Also, numerical simulation of electric field distribution is performed for verification, taking the surface arc development into account. It indicates that the development of surface arc is distorted by the coating which results in the intense local field and dielectric breakdown. Next, different controlled experiments are designed and conducted to validate the theory. Besides, the corresponding modification towards the current coating method is proposed. [ABSTRACT FROM AUTHOR]

This paper is aimed at a systematic study of the leakage current of high voltage polyamide insulator string under different conditions of pollution for possible application in the electric locomotive systems. It is shown that in the case of clean/dry and clean/wetted insulators, the leakage current and applied voltage are linear. While in the case of pollution with saline spray, the leakage current and the applied voltage are not linear; the leakage current changes from a linear regime to a nonlinear regime up to total flashover of the insulators sting. Traces of erosion and tracking of insulators resulting of partial discharges are observed.

Pollution flashover is harmful and has caused huge economic losses. Thus, it is important to evaluate the contamination condition of insulators to prevent the pollution flashover. The objective of this paper is to discriminate the insulator contamination grades by the noncontact method. In this paper, a method of visible light images assisted with infrared information is proposed. The proposed method evaluates the contamination condition using the visible light images, and is corrected by the infrared information in the wet environment. A mathematical model is established to study the relationship between the equivalent salt deposit density (ESDD) (mg/cm2) and the color features. The influences of illumination L and relative humidity (RH) on the color features are analyzed and their eliminated methods are proposed. The infrared image information is proposed to assist the visible light image method when RH ≥ 60%. In the experiment, the visible light images of the artificial polluted insulators are acquired by a digital camera under different illuminations L and RHs, and the average value of V component Vave in the YUV color space is selected for the discrimination of contamination grades. In the test, the proposed method gives an 84% accuracy rate when RH < 60% and gives an 89% accuracy rate when RH ≥ 60%. Finally, naturally polluted insulators were tested. The general test error of ESDD is about 0.0119 mg/cm2. Therefore, it might be concluded the condition of naturally polluted insulators could be evaluated by the proposed method of visible light images assisted with infrared information. [ABSTRACT FROM PUBLISHER]

Accurate and timely detection of insulator flashover on power transmission lines is of paramount importance to power utilities. Most available solutions mainly focus on the exploitation of the flashover mechanism or the discharge area detection, rather than the identification of a damaged area due to flashovers using captured aerial images. To this end, this paper proposes a multi-saliency aggregation-based porcelain insulator flashover fault detection approach. The target area of the insulator is determined using the Faster-Pixelwise Image Saliency by Aggregating (F-PISA) algorithm based on the color and structural features. The color model can be established based on the color feature of the damaged areas on the insulator surface, and hence the damaged area can be identified. Based on the information obtained above, the contour information can be extracted. With the preceding process, the fault location can be confirmed with a good accuracy. The performance of the proposed detection approach is assessed through a comparative study with other available solutions. The numerical result demonstrates that the suggested solution can detect the insulator flashover with improved performance in terms of the average detection rate and average efficient detection rate. Additional analysis is carried out to evaluate its robustness and real-time performance, which confirms its deployment feasibility in practice. [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]

Flashover is a disorder condition that occurs in the form of sparks appearing between insulators or electrical component of high voltage. This can occur due to insulation failure of the high voltage system. Failure of insulation in high voltage insulators in Tanjung Jati B Jepara Substation is one of the causes of acid rain due to the condensation of smoke from the Tanjung Jati B power plant chimney. Acid rain arises due to failure Flue Gas Desulphur ( FGD ) devices were installed in the plant to reduce gas emissions as a condition of eco-friendly power plant that is planned by the government through the department of Environment. The real action is taken to dismiss the notion that Coal Fired Power Plant (CFPP) is one of the industries that emit SOx and NOx emissions are high on operational processes. The effects of gas emissions is one of the causes of acid rain on the environment. The amount of acidity of acid rain that occurred in the industrial area will always affect the high voltage power lines that distribute power in operation. Sometimes the equipment functions as an insulator in high voltage substations that distribute power at 500 kV network SUTET JAMALI network on the island of Java in a system of operation is interrupted because of pollutants attached to the insulator. Rain with a pH between 4-5 categorized as acid rain and the test affects the time of the flashover voltage drop of 145.5 kV – 142.5 kV of the working voltage , this causes an insulator as insulation materials can be minimized distance insulator surface so that termites can affect the resistance of an insulator in its function as a tool to restrain the occurrence of flashover voltage from voltage parts.

Pollution materials affect insulator flashover performance, and there is long-term significance in researching it. In this paper, common kinds of nitrates were used as the soluble pollution, and the ac flashover performance of four types of insulators under different nitrates were investigated. Basing on a large amount of primary data, the calculation of flashover gradient in specific to different pollution materials was discussed, and the effects of nitrates on it were analyzed. Research results indicate that, flashover gradient of insulator under nitrates is commonly higher than that under NaCl; among the nitrates, KNO3 corresponds to lower insulator flashover gradient while Ca(NO3)2 corresponds to a higher one; the exponent b, which characterizing the influence of ESDD on flashover gradient, is lower under nitrites than that under NaCl; for the four insulator samples polluted by nitrates, the flashover gradient of the porcelain type can be expressed by A?ESDD?0.21?NSDD?0.16, the flashover gradient EL of the glass type can be expressed by A?ESDD?0.22?NSDD?0.14, while that of the composite samples can be expressed by A?ESDD?0.19?NSDD?0.13. Research data may provide references for the better prediction of flashover voltage as well as for the better design of external insulation. [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]

Accurate and timely detection of insulator flashover on power transmission lines is of paramount importance to power utilities. Most available solutions mainly focus on the exploitation of the flashover mechanism or the discharge area detection, rather than the identification of a damaged area due to flashovers using captured aerial images. To this end, this paper proposes a multi-saliency aggregation-based porcelain insulator flashover fault detection approach. The target area of the insulator is determined using the Faster-Pixelwise Image Saliency by Aggregating (F-PISA) algorithm based on the color and structural features. The color model can be established based on the color feature of the damaged areas on the insulator surface, and hence the damaged area can be identified. Based on the information obtained above, the contour information can be extracted. With the preceding process, the fault location can be confirmed with a good accuracy. The performance of the proposed detection approach is assessed through a comparative study with other available solutions. The numerical result demonstrates that the suggested solution can detect the insulator flashover with improved performance in terms of the average detection rate and average efficient detection rate. Additional analysis is carried out to evaluate its robustness and real-time performance, which confirms its deployment feasibility in practice.

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 PUBLISHER]

After the formation of local violet arcs across air gaps on an ice-covered insulator, which is the first step of the flashover process, these arcs can extend along the ice surface and form a white arc under certain conditions. The white arc can propagate on the ice surface and reach a critical length of about two-thirds of the dry arc distance. This step, which includes the formation of a white arc and its propagation to a critical length, is the second step of the flashover process. It plays a crucial role because after this step the electric field between the column and root(s) of the arc and ground electrode (or HV electrode or both electrodes) is sufficient to result in a complete flashover at the third step. Besides the electrical breakdown process ahead of the arc column, increasing the thickness of the surface film, made of highly conductive water, on an ice surface may play a significant role in the movement of the arc root during the second step. Film thickness increase is mainly due to heating effect of the arc root temperature and joule heating of flowing leakage currents through the surface film. In this paper, the heating effect of the positive dc arc root temperature on the thickness of the surface film is accurately modeled and studied using COMSOL Multiphysics, a commercial software. Rotational temperature of an arc formed over an ice surface, which was measured in previous studies at CIGELE through optical emission spectroscopy, will be used as input parameter in the model. The simulation results show that the time taken for heat transfer to increase ice temperature from − 12 °C to its melting temperature is only a few seconds and can thus influence the arc root movement during the second step. The obtained results allow improvement over the previous hypothesis consisting of ignoring heat transfer effects of an arc during its propagation over the ice surface. These findings will be useful to improve prediction of critical flashover voltages of ice-covered insulators. [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 PUBLISHER]

In order to investigate the ice flashover performance and characterization parameter of composite insulators, numerical calculation was applied to simulate the icicle growth and make comparison with different structures. It was found that the number of booster sheds existed an optimized range and saturated icicle bridged degree of big sheds or booster sheds could be considered as the characterization parameter to reflect the ice flashover voltage. Booster sheds applied to 500 kV composite insulators show its advantage on anti-icing performance. However, when design for lower structural height insulators, such as 110 kV composite insulators, excessive booster sheds could form a shorter flashover path. Experiments show there is a good corresponding relation between flashover voltage and saturated icicle bridged degree. Moreover, when applied to 500 kV composite insulators, saturated icicle bridged degree of big sheds dominated the flashover process, while the value of booster sheds played more important role for 110 kV samples. [ABSTRACT FROM AUTHOR]

This paper presents a probabilistic model for insulator flashover based on numerical electric field calculation and random walk theory. The advancement to the state-of-the-art lies in the ability of the model to consider realistic events like arc jumping between the sheds by evaluating the electric field on the insulator surface and in the immediate vicinity of the insulator in an efficient manner. For high ESDD values (above 0.1 mg/cm2), the results from the proposed model and deterministic model are not significantly different. For ESDD values in the range 0.01-0.1 mg/cm2, which represents the majority of locations, the values obtained by the statistical model are closer to experimental results than obtained from the deterministic model. The model presented is for insulators using non-hydrophobic materials, such as porcelain, glass and several polymers. [ABSTRACT FROM PUBLISHER]

Electrode erosion is a notable issue influencing the performance and restricting the lifetime of gas switches. In the erosion process, electrode materials heated by spark channel will melt or evaporate and be driven to depart from electrode surface, contaminating the gas switch insulator, and potentially inducing flashover accidents. In this paper, sputtering spots are observed near the erosion crater in a two-electrode gas switch, which indicates the existence of molten droplet ejection. In addition, a set of polymethyl methacrylate rings are inserted in the gas switch to detect the ejection of molten droplet as well as to simulate the switch insulator for investigating the degradation of surface insulation strength. The results show that the ejection of molten droplet is along the tangent surface of electrode with a small divergent angle. After repeated discharges, the insulator surface is bombarded by the droplet ejection and forms dense cracks and embedded metal particles in a narrow band. The spatial varied droplet ejection causes a decrease in both flashover electric field and surface resistance. It also leads to different surface resistances in different regions, which can result in an uneven electric field distribution. Thus, droplet ejection increases the probability of surface flashover accidents in gas switches. [ABSTRACT FROM PUBLISHER]

The type of pollution materials may influence the flashover performance of an insulator. In this paper the pollution flashover performance of a 7-unit insulator string, consisting of typical discs, is determined by laboratory tests while varying the weight percentage of soluble (NaCl and CaSO4) or non-soluble (SiO2, Al2O3 and Fe2O3) materials. When studying the effect of pollution materials on flashover performance, the influence of volume conductivity and equivalent salt deposit density (ESDD) under different weight percentages of soluble materials is firstly investigated, and then the underlying factor, the thermal ionization of pollution materials, is considered. Finally, the measurement results of leakage current under different pollution materials are presented. The research results indicate that the effect by weight of CaSO4 is not as severe as that of NaCl, and the reason is not just its effect on the layer conductivity and ESDD, but its effect on the thermal ionization during the arc propagation process may also be one of the key factors. The fact that a small amount of Al2O3 and Fe2O3 causes the flashover voltage to decrease by 20%, may result from the lower ionization potentials and the higher leakage currents caused by non-soluble materials containing Al2O3 and Fe2O3. [ABSTRACT FROM AUTHOR]

Ice morphology was established from field failure observations on electrical insulators, considering partial and full bridging conditions. Small scale laboratory simulations showed an important effect of droplet ejection on the probability of flashover. During the experiments, factors including applied water conductivity, icicle length, combinations of air gap and icicle length and duration of melting period were investigated using typical in-service stress levels. According to the experimental results, applied water conductivity and icicle length affected the residual ice layer resistance. Flashover voltage decreased by 33% as the conductivity increased from 150 μS/cm to 750 μS/cm and reduced by 10% as icicle length declined from 6 to 4 cm for constant 2-cm air gap. Fully bridged icicles required extra energy for ice melting, leading to higher flashover voltage compared to partially bridged icicles of the same morphology. A single 3-cm air gap had 14% higher flashover voltage than a pair of 1.5 cm air gaps. [ABSTRACT FROM AUTHOR]

In bridged vacuum gaps, it is believed that the secondary electron emission avalanche (SEEA) and the resultant insulator charging play a crucial role in the progress of discharge leading to the surface flashover. This paper deals with the electric field just before the flashover that includes the accumulated SEEA charge component (EsF) and applied geometrical field component (EgF) on a cathode and their relation to the flashover voltage. The test gap consists of parallel disc electrodes bridged by an insulating solid cylinder made of Al2O3. The test insulator changes its length from 5 to 50 mm. As it has been clarified in our previous works that surface roughness of the insulator affects SEEA charge accumulation, we have examined the roughness ranging from 0.2 to 6 ?m. Aluminum electrodes are mainly examined, and copper and stainless electrodes are used for comparison. A ring type electrostatic probe embedded near the triple junction on the cathode is employed to measure the electric field. As a result, the total field strength (EgF + EsF) for various insulator conditions with aluminum electrodes is 6.7 kVmm-1 as an average. However, the rate (?) of SEEA charge component that accounts for the total electric field varies according to the insulator length and the roughness. When ? exceeds ca. 15%, the flashover voltage Vb depends on the square root of the insulator length. On the other hand, Vb is a linear function of the insulator length when the SEEA charging is depressed and thus ? is smaller than 15%. On the condition that ?<15%, the material of electrode makes an impact on the flashover voltage. [ABSTRACT FROM AUTHOR]

Under continuous wind of single direction, the leeward area of insulator string may be polluted more seriously than windward area, making the pollution layer distributes like a fan-shape. In this paper, dc pollution flashover tests of 7-unit XP-70 insulator string with fan-shaped non-uniform pollution were carried out. Then the influence of fan-shaped non-uniform pollution on flashover voltage, flashover process, leeward side surface layer conductivity and surface pollution layer resistance were discussed. Research results indicate that, the ratio W/L of windward to leeward side salt deposit density (SDD) affects the dc flashover performance of insulator string. A reduction in W/L from 1/1 to 1/15 would give a decrease of 28% in flashover strength. Flashover voltage may also decrease when the occupation ratio (T) of leeward side increases from 10% to 30%. Under fan-shaped non-uniform pollution, U50 can still be expressed by a negative exponential function of SDD, and the effect of fan-shaped non-uniform pollution on U50-SDD relationship may mainly lie in changing the proportionality coefficient a rather than the exponent n; discharge path was restricted along the leeward side, which may make the air-gap arc easily formed and benefit the flashover process. [ABSTRACT FROM AUTHOR]

In December 2005, Japan experienced a major outage in Niigata Kaetsu area due to a large amount of wet snow mixed with sea-salt accreted on several transmission line insulators. To clarify the causes of the snow-induced outage and increase reliability of the networks, a 154 kV class full-scale snow test procedure to evaluate various insulator designs was developed, and artificial flashover voltage tests of snow accreted insulators were carried out. High voltage flashover tests showed that the flashover voltage of both long-rod and cap & pin insulators was decreased with the increase of snow conductivity. Also, cap & pin insulators showed significantly higher flashover voltage than long-rod insulators. Thus substitution of long-rod insulators with cap & pin insulators appears to be reasonable as a countermeasure against snow induced flashovers. [ABSTRACT FROM PUBLISHER]

The Rapid Flashover pollution test method (RFO) exposes energized polluted insulators to fog and uses step changes of voltage to identify a minimum flashover voltage. The RFO method reduces test time by a factor of three or more compared to up-and-down voltage application method and is thus time- and cost-effective. In this paper the results from RFO on five ceramic and composite station insulators (line, post and hollow) with median 4.7 m leakage distance are compared closely with duplicate tests using up-anddown procedure. The tests on hydrophobic composite insulators used the preconditioning principles from CIGRE Brochure 555. Full-scale withstand testing of the same five but 420-kV class voltage insulators with median leakage distance 13.3 m are also presented. It is indicated that the flashover test results of RTV-coated station insulators should be specially analyzed and treated. [ABSTRACT FROM PUBLISHER]