Flashover dynamic model of polluted insulators under ac voltage

This paper presents a dynamic model allowing the prediction of discharge activity leading to flashover of polluted insulators. It takes into account the instantaneous changes of the discharge (arc) parameters. For a given voltage, geometry and pollution severity, the model enables one to determine the following parameters: temporal evolution of the current, arc resistance, propagation velocity, charge injection and flashover time lag. The flashover voltage characteristic as a function of the surface conductivity of insulators calculated by this model is quite satisfactory in contrast to the empirical and semi-empirical models reported in the literature. The leakage currents computed by our model are found to be in a good agreement with those measured in the laboratory     

Vacuum flashover on diamond-like carbon-coated insulators

Thin coatings of diamond-like carbon (DLC) were applied to cylindrical alumina and high temperature polyimide insulator samples. The coated insulators and uncoated controls were tested for resistance to surface flashover in vacuum under a dc voltage gradient. The DLC-coated insulators had significantly higher flashover potential than the controls and showed no visible tracking on their surface, even after multiple discharges. DLC coatings, applied at temperatures <350°C, show promise for improving the performance of HV vacuum feedthroughs, switches, and in other applications     

污秽绝缘子闪络特性试验研究

通过EMTP仿真分别获取0.5/5μs和2.6/50μs绝缘子串反击和绕击条件下的电压波形,并选取电阻-电容隔离回路作为工频回路与冲击电压发生器的隔离电路,同时确定污秽绝缘子制备方法和湿润方式。通过试验,得到在0.5/5μs和2.6/50μs两种冲击电压波形条件下,污秽绝缘子在工频叠加冲击时闪络电压变化的基本规律。     

覆冰绝缘子交直流闪络场路模型的研究

该文建立了覆冰绝缘子的交直流闪络场路模型,该模型将覆冰绝缘子的闪络分为空气间隙击穿前电弧的起始、空气间隙击穿后电弧在冰表面的发展和临界闪络判定3个阶段。通过对空气间隙击穿前后覆冰绝缘子电场分布的计算,并结合覆冰绝缘子闪络电路模型中电弧的E-I特性和U-I特性,求取覆冰绝缘子的临界闪络电压和电流,进而求取闪络过程中的U-I特性和I-t特性,并可以避免用电路模型采用简化公式计算覆冰各参量所产生的误差。通过与其他理论模型计算结果和真实覆冰绝缘子的试验结果的比较,对该文所建立模型进行了验证。     

Outdoor HV composite polymeric insulators

HV composite polymeric insulators are being accepted increasingly for use in outdoor installations by the traditionally cautious electric power utilities worldwide. They currently represent ~60 to 70% of newly installed HV insulators in North America. The tremendous growth in the applications of non-ceramic composite insulators is due to their advantages over the traditional ceramic and glass insulators. These include light weight, higher mechanical strength to weight ratio, resistance to vandalism, better performance in the presence of heavy pollution in wet conditions, and comparable or better withstand voltage than porcelain or glass insulators. However, because polymeric insulators are relatively new, the expected lifetime and their long-term reliability are not known and therefore are of concern to users. Additionally they might suffer from erosion and tracking in the presence of severe contamination and sustained moisture. This leads to the development of dry band arcing that under certain circumstances could lead to failure of polymer insulators. In this paper a review is presented of the recent performance experience of HV composite polymeric insulators in outdoor service, testing methods, aging, the ranking of the materials, the role of fillers, the role of low molecular weight components present in the insulators, the mechanisms responsible for the loss and recovery of hydrophobicity, one of the most important properties of polymers, the mechanisms of failure, detection of faults, type and quantity of natural contaminants, effects of exposure to rain, hydrocarbons, stationary air and wind, various methods to optimize the electrical performance and a relatively new method for evaluating the performance status of polymeric insulators in the field     

The pollution flashover on high voltage insulators

The pollution flashover, observed on insulators used in high voltage transmission, is one of the most important problems for power transmission. It is a very complex problem due to several factors such as the modeling difficulties of complex shapes of the insulators, different pollution density 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 were developed by making some assumptions and omissions to predict the flashover voltages of polluted insulators. In this study, historical development of insulator modeling was investigated and a dynamic arc model was proposed. For this purpose, scaled shape of a concerned insulator was firstly partitioned into triangular elements, then finite element method (FEM) was implemented and finally potential distribution on the insulator surface, variation of pollution resistance and flashover voltage were determined. The computed flashover voltage values of the selected string insulator have been compared to results from other research.     

Sudden flashover of nonceramic insulators in artificialcontamination tests

This paper presents experimental and theoretical results to explain the phenomenon of sudden flashover on artificially contaminated nonceramic insulators. A sudden flashover in this paper is defined as a flashover occurring on a partially contaminated insulator, and which is preceded by little or no surface discharge activity. Sudden flashovers could occur in the field on those insulators where the wet surface resistance varies over a wide range along the insulator length. The mechanism of sudden flashover is significantly different from conventional contamination flashover that occurs in standard contamination tests. The insulators evaluated had weathersheds made from silicone and ethylene propylene diene monomer (EPDM) rubbers. The impact of the present study from the point of view of weathershed material, insulator design, development of a comprehensive laboratory test and field monitoring for evaluating the performance of nonceramic insulators in service are discussed     

Leakage current and flashover of field-aged polymeric insulators

In this paper results from leakage current (LC) measurements under steam fog and voltage withstand tests under rain conditions obtained on various field aged polymeric insulators are reported. Included in this work are several silicone rubber (SIR) and ethylene propylene diene monomer (EPDM) rubber insulators of ac and dc design that have been energized at suitably high ac and dc voltages under coastal conditions for a period of more than nine years. Their performances are compared to two sets of identical insulators, namely one that was outdoors exposed without being energized and one that was stored indoors. The LC of each insulator was studied three times, namely as received from the field, after it was gently washed to remove soluble pollution, and finally after a voltage withstand test. In between the measurements, the insulators were left to recover for a period of a week. The results show that the LC of the SIR insulators were generally lower than those of the EPDM. In both cases, the LC of the insulators that were stored indoors were significantly lower than those of the outdoor exposed insulators. The voltage withstand tests revealed an almost linear relation between the flashover voltage (FOV) and the arcing distance of the insulators. In general, for similar SIR and EPDM insulators the FOV of the SIR ones were higher than those of EPDM insulators     

Surface charging and flashover on insulators in vacuum

Investigations have been carried out on right cylindrical Teflon spacers in vacuum under dc stress to study the effect of cathode geometry on surface charging and flashover. Three cathode support arrangements were used. Type 1 involved a recess in the cathode into which the spacer was located, type 2 was a simple flat plate cathode, while type 3 had a raised insert on the cathode surface over which the spacer was located. In all cases the surface charge density and distribution is primarily dependent upon the magnitude of the electric stress. Using the type 1 arrangement inception for charge deposition was always ~10 kV even when the spacer had been subjected to repeated flashovers. At applied voltages higher than this the density of the charge, which was fairly uniformly distributed around the surface, was more or less proportional to the applied voltage. For the type 2 and type 3 arrangements, a distinct, uniformly distributed negative charge of ⩽20 μC/m² was always detected at low values of applied stress and at a fairly well-defined transition voltage this gave way to a distribution which was substantially uniform in the case of type 2 but quite filamentary in type 3, and both involved the deposition of positive charge     

AC flashover performance of insulators covered with artificial ice

A field observation of ice accretion on Hydro-Quebec HV insulators was carried out, as well as a laboratory investigation of the AC flashover performance of various types of insulators covered with artificial ice. The field observations made it possible to identify the type and physical aspect of naturally occurring ice accretions produced during freezing rain precipitation. The laboratory investigation was conducted in a 4.8×2.8 m×3.8 m climate room using a HV transformer of 120 kV, 240 kVA with a short-circuit impedance of 5%. A method based on the standard IEC 507 method was developed for measuring the maximum withstand voltage (V_WS) of ice-covered insulators. Various factors were investigated, including the effects on the insulator V_WS of such particulars as type, thickness, and uniformity of the ice, as well as the arcing distance of the insulators and the conductivity of freezing water. The effects of uniform ice, 2 cm thick, on 5 IEEE insulator units was thus considered to be equivalent to the effect of an ESDD of about 0.13 mg/cm² on the same insulators     

直流线路绝缘子冰闪特性研究

叙述了在人工气候室内对不同形式绝缘子进行的覆冰直流闪络特性研究,根据试验结果分析了不同直流绝缘子的闪络特性,并研究分析了人工污秽与自然污秽对冰闪电压的影响.结果表明,不同材质和型式的绝缘子对覆冰直流闪络电压影响不大,随着冰厚增加以及污秽增加,覆冰直流闪络电压都会下将,提出了绝缘子串直流U50%闪络电压与覆冰厚度及污秽的关系表达式,指出自然污秽下绝缘子的冰闪电压高于相同污秽状况下的人工污秽绝缘子.     

线路污秽绝缘子的在线监测

架空输电线路在运行过程中 ,空气中的尘土、盐碱、工业烟尘等各种微粒或鸟粪都会堆积在绝缘子外表面形成污秽层。绝缘子的污秽程度与其造型、环境污秽种类及程度、线路附近气候条件等因素有关 ,绝缘子的积污是指绝缘子运行一定时间后表面污秽所达到的饱和值 ,即粘附在绝缘子表面的污秽和被雨水冲刷掉与被风吹掉的污秽在宏观上所达到的动平衡状态。在整个积污过程中 ,当受到雨水的自洁作用 ,绝缘子表面的污秽呈锯齿状下降 ,然后再逐渐上升。在未达到饱和值前 ,总的趋势污秽为上升状态 ,直至达到饱和值为止。实际上架空输电线路绝缘子表面的污…     

The pollution flashover of ac energized post type insulators

This paper investigates the application of a theoretical model to predict the flashover of practical post type insulators. In particular, the model is applied to two 132 kV designs with different profiles and leakage path lengths. It is found that arc shortening due to inter-shed and inter-rib flashover and arc movement results in a significant deterioration of the pollution performance of the insulator. The theoretical results are confirmed by salt fog tests and field experience     

输电线路绝缘子冰闪防治措施的研究

结合湖南省电网的基本情况,进行覆冰绝缘子(长)串交流闪络特性的仿真试验研究,找到冰闪形成的机理和规律,根据影响冰闪的因素,探索合理的防冰闪技术措施;建立有限元仿真模型,进行受力分析,提出了防治冰闪的综合措施.     

Flashover of discontinuous pollution layer on HV insulators

This paper deals with discontinuous pollution layers deposited on the insulator surface. Two zones are known to form: a clean (dry) zone and a polluted (wetted) zone. The influence of the length and position of the dry zone on the leakage current and the arc length are investigated. These were made on a plane experimental model under ac voltage. Two configurations were studied: pollution deposited near the HV electrode, and pollution deposited near the ground electrode. This study was made using pollution layers with different conductivities. Based on the experimental results, a theoretical model allowing us to calculate the gap impedance, the transferred (gap) voltage and the leakage current was established. This model enables to predict the pollution severity based on the sample's equivalent impedance     

Role of non-soluble contaminants on the flashover voltage ofporcelain insulators

The influence of non-soluble or inert contaminants on the flashover voltage of HV outdoor porcelain insulators is examined. A dynamic arc model, presented earlier for predicting the flashover voltage of porcelain insulators covered with water soluble contaminants, has been modified suitably. The extended model has been used to predict the flashover voltage of suspension and station post insulators of various shapes for both ac and dc voltages. Good correlation with experimental data has been shown. The model can thus be used as a computer aided tool for design and maintenance of HV porcelain insulators     

运行多年RTV涂料绝缘子防污性能的研究

室温硫化硅橡胶(RTV)涂料具有优异的憎水性和憎水迁移性,可显著提高瓷和玻璃绝缘子的污闪电压,目前已在电力系统广泛应用。通过以挂网运行多年后的RTV涂料绝缘子为试品,对RTV涂层表面的积污状况、憎水性、憎水迁移性和憎水性丧失后的恢复能力及试品在长时间饱和受潮条件下的耐污闪能力进行研究,研究结果对RTV涂料在输电线路绝缘子上的使用提供了有力的技术支持。     

Field solution in polluted insulators with non-symmetric boundaryconditions

A finite difference (FD) method to calculate the electric field in polluted insulators with asymmetric boundary conditions is proposed. The method is based on neglecting the displacement currents that circulate through the porcelain and through the air, in comparison with the conduction currents that circulate over the semiconductive pollution layer covering the insulator. This assumption reduces the 3D problem to a 2D one over the insulator surface. The FD method is applied by superposing a grid composed of parallels and meridians over the insulator surface, setting up an FD equation for each mode, and solving the resultant set of simultaneous equations     

A fuzzy logic optimization methodology for the estimation of the critical flashover voltage on insulators

The objective of this paper is to present a new methodology for predicting the critical flashover voltage of polluted insulators based on fuzzy logic. The prediction contains not only the estimated value, but also the respective confidence interval based on the re-sampling method. Various parameters, such as the number and the base width of the triangular membership functions used for the fuzzification process, etc., are assigned different values in order to optimize the estimation of the critical flashover voltage. Additionally, different methods for training the fuzzy system are applied and compared for their appropriateness in accurately predicting the critical flashover voltage.