Dynamics and modeling of AC arc on surface of ice

A self-consistent dynamic model allowing the prediction of AC discharge activities leading to flashover on ice-covered insulator surface is presented. This model takes into account the effects of a number of parameters including insulator geometry and applied water conductivity. The instantaneous variations of major parameters are discussed in order to develop a sequential time-dependent simulation of the flashover. The temporal evolution of arc current and axial arc velocity are determined in a consistent manner. The critical flashover voltage characteristics, as a function of surface conductivity, insulator length, and insulator diameter, calculated by the model are quite satisfactory when compared to the experimental results from empirical models reported in the literature     

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。     

Modeling of DC Flashover on Ice-Covered HV Insulators Based on Dynamic Electric Field Analysis

In this paper, a model based on dynamic electric field analysis has been developed to predict the flashover voltage of the ice-covered HV insulators, under dc voltage. The potential and electric field calculation models before and after air gap breakdown are built respectively based on finite element method (FEM). The arc initiation process is determined based on the model before air gap breakdown. The critical applied voltage and leakage current to maintain an arc with certain length are obtained based on the electric field calculation model after air gap breakdown and the U-I characteristic of the arc. Moreover, the improved Hampton criterion has been employed to determine the critical flashover of the ice-covered insulator. The results obtained from the dynamic electric field analysis model have been compared with other mathematical and experimental results of other researchers and got a great agreement.     

A combined engineering model for the analysis of switching surge flashover characteristics of long air gaps

The flashover characteristics of long air gaps submitted to switching surge voltages may be predetermined by use of a mathematical model of leader propagation. The present model is developed from each combination of previous engineering models, and is also applied to positive rod-to-plane geometries with gap lengths up to 20 m. However, four parameters to determine leader propagation with respect to our model are adjusted in the present calculation so as to fit experimental flashover voltages and calculated flashover voltages which depend on waveforms of the applied voltage and gap length. The calculations show that these parameters are only a function of gap length. Our combined engineering model using parameters that depend on gap length allows the flashover characteristics of long air gaps to be easily determined with a microcomputer.     

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     

污秽绝缘子闪络机理研究综述

文章综述了几十年来国内外对污秽绝缘子闪络机理的研究状况,包括电路模型、能量模型、动态模型、交流电弧重燃条件、电场模型以及低气压下的电弧特性等,并根据真型绝缘子串污闪放电过程的拍摄结果,提出了由剩余污层电阻、沿面电弧和空气间隙电弧串联组成的低气压下绝缘子长串直流放电数学模型,同时对未来绝缘子污秽闪络机理的研究方向进行了展望,指出真型绝缘子长串放电过程、绝缘子剩余污层电阻、低气压下局部电弧特性的测量等是今后研究的重点。     

交流污闪电弧动态特征探究

通过将污闪电弧模型化,并结合有关污闪试验结论和物理学说,详细讨论了在交流冲击下,污闪电弧的动态特征。绘制了起弧、电弧延伸、临界态、电弧收缩、熄弧各状态之间的电弧状态发展轨迹,将径向延伸和“电容效应”引入了电弧动态方程。从而揭示了电弧发展过程中有关状态量的变化趋势和特征,并针对有关结论做了必要的解释和验证。结果表明:电弧的延伸和收缩状态轨迹不是重合的,考虑弧径延伸和“电容效应”能够弥补现有模型的不足。这对于进一步研究污闪机理,建立更加科学合理的污闪模型具有参考价值。     

低气压下空气间隙电弧对覆冰绝缘子串直流闪络的影响

覆冰绝缘子串在直流闪络过程特别是低气压条件下中易产生空气间隙电弧形成"飘弧"现象,飘弧易桥接覆冰绝缘子串,且空气间隙电弧和冰面电弧具有不同的伏安特性,而传统的覆冰绝缘子串直流闪络模型由冰面电弧和剩余冰层电阻构成,没有考虑空气间隙电弧,在低气压下计算结果与实际情况相差较大。为了解此一现象,首先从理论上分析了飘弧对低气压下覆冰绝缘子串直流闪络电压的影响,建立了考虑和忽略空气间隙电弧的覆冰绝缘子串直流闪络模型,根据理论模型计算了相应的闪络电压,并与试验结果进行了比较分析。试验与理论计算结果表明,飘弧现象随着气压的降低和绝缘子串覆冰及污秽的程度增加而增加,低气压下进行绝缘子串直流闪络建模、预测和特性试验时应考虑空气间隙电弧及其飘弧的影响。     

交流电弧沿染污绝缘表面发展过程的研究

作者用高速摄影机拍摄了交流电弧沿染污绝缘表面发展的全过程,同时记录闪络过程中外施电压和泄漏电流的变化。通过综合分析,阐述了交流污闪电弧的物理特征,电弧的极性效应、电弧延伸的最大速度以及临界闪络电压、电弧长度,为研究污秽闪络机理提供了科学的依据。     

110 kV覆雪绝缘子串电场有限元仿真分析

近年来,我国内陆重污区输电线路在冬季频发短时积污雪而引起的快速污雪闪。快速污雪闪相比于传统污闪具有以下显著特点:一是地域性,快速污雪闪多发生在内陆重工业污染地区久旱之后的降雨雪过程;二是短时性,绝缘子在短时间内快速受潮且积污严重湿润,其污秽条件与受潮条件几乎是同时具备。为了研究覆污雪对输电线路外绝缘电气性能的影响,对覆雪110 kV绝缘子串进行了三维建模与电场仿真研究。结果表明,覆雪会畸变绝缘子串电位分布,导致导线侧与杆塔侧绝缘子分担电压显著提升;当绝缘子表面严重积雪并形成雪柱时,绝缘子串有效爬电距离被短接,污雪柱之间空气间隙电场畸变严重,电场增强约27.5倍,易形成"污雪柱-空气间隙-污雪柱"放电通道,从而引起绝缘子串闪络。     

A new flashover dynamic model of polluted HV insulators

In this work, a model based on field criterion has been developed to represent the flashover phenomenon, which occurs due to surface pollution on high voltage insulators, under ac voltage. The values of potential and electric field on an insulator surface have been determined using the finite element method (FEM). The open model of the insulator has been used for calculating the resistance in series with the arc, in addition to the values of the leakage current and the arc gradient. As a new approach, this dynamic model uses Lagrange multipliers for the solution of the pollution flashover problem. Both the impedance and the electric field criterion have been used for the propagation of arc on the surface. A computer program called NFDM (new flashover dynamic model) has been developed to achieve this. The results obtained from the program have been compared with theoretical and experimental results of other researchers.     

Polluted insulator flashover model for ac voltage

Considerable theoretical and experimental research on polluted insulators has yet to yield a perfect generalized mathematical model which can predict accurately critical flashover voltages and currents. In this paper an ac model has been proposed especially applicable to static arcs. The salient feature of the proposed model is that it takes into account the appropriate selection of arc constants for different chemical nature of the pollutants. The computed results closely follow the experimental curves and can predict rms value of critical flashover voltages with a mean absolute error (MAE) of <4%. The validity of the model was verified by comparing the computed results of rms critical flashover voltages and currents against experimental and theoretical data of other researchers for a number of practical insulators of different geometries and good agreement has been obtained     

35～1000kV线路绝缘子污闪电压值的估算

针对目前绝缘子污闪电压缺乏系统研究的现状,建立了35~1 000 kV输电线路用普通型绝缘子交流污闪电压的计算模型即展开普通型绝缘子成平面模型后分析交流污闪条件,计算出绝缘子在不同表面污层电导率条件下的临界污闪电压值;对35~1 000 kV输电线路用5种不同吨位的普通型绝缘子进行交流人工污秽试验,获其在各盐密下的50%污闪电压;通过计算值和试验值的对比,可将绝缘子表面污层电导率转化为盐密,从而算出各普通型绝缘子在不同盐密下的交流污闪电压值。试验验证计算结果误差小,说明该模型能够有效估算代表普通型绝缘子的50%污闪电压情况。该研究结果可供各电压等级输电线路外绝缘选择参改。     

XZP/XZWP4-160直流绝缘子覆冰闪络电弧特性的研究

在人工气候室内对覆冰XZP/XZWP4-160绝缘子的闪络特性及放电发展过程进行了试验研究。根据试验结果进行分析得出:弧根周围空气的热电离导致了电弧的发展,静电场力对电弧的发展起到了加速作用,电击穿仅发生在闪络最终的跳跃阶段;通过测量闪络过程中的放电电压、泄漏电流、闪络时间、覆冰水电导率、电弧长度及电弧半径等参数,得到电弧的发展速度及临界电弧长度均随覆冰水电导率的增加而减小,弧根电流密度随着气压的降低而增大;与正极性电弧相比,负极性电弧的发展速度快且弧根半径大。进一步分析覆冰绝缘子的闪络过程可知:覆冰绝缘子存在2个不同的闪络路径,即沿冰层外部和内部,这是由于电弧热作用蒸发的Na原子进入弧柱的方式不同造成的。     

Effects of low air pressure on AC and DC arc propagation on ice surface

The effects of air pressure on the AC and DC arc process on an ice surface, including velocity, parameters and flashover voltage, were studied. The results obtained showed that air pressure has an obvious influence on the arc propagation velocity, arc constant A, electrode voltage drop V_e and consequently on the flashover voltage of the ice surface, V_f. This decrease in V_f is explained by the decrease in the E-I arc characteristics and arc propagation velocity, and by the relatively higher density of Na atoms in the arcs at pressures below standard air pressure. Based on these results, the mechanism underlying the decrease in the flashover voltage of ice-covered insulators at high altitude was analyzed     

染污绝缘子串直流污闪放电的电路模型

绝缘子污秽闪络事故严重威胁电力系统的安全可靠运行,目前国内外对污闪机理的研究主要以平板模型为基础。以7片串XP–160绝缘子为例,开展染污绝缘子串直流污闪电路模型的研究。根据高速摄像机拍摄的结果得知,染污绝缘子串直流污闪放电过程中局部电弧存在飘弧现象,即局部电弧由沿面电弧和空气间隙电弧2部分组成;提出染污绝缘子串直流放电过程的电路模型由剩余污层电阻、沿面电弧和空气间隙电弧串联组成;根据模型推导得到染污绝缘子串直流污闪电压的污秽影响特征指数在0.22~0.34之间,并从理论上解释了不同型式绝缘子污秽影响特征指数存在差异的原因。     

Prediction parameters of dimensioning of insulators under non-uniform contaminated conditions by multiple regression analysis

Surface tracking on solid insulators is one of the most severe breakdown mechanisms. Accurate assessment of real insulation conditions can be achieved by using the statistical techniques that assist the measurement and monitoring of contamination severity, flashover voltage and leakage current.To address the uncertainties that surround the exact physical mechanisms underlying the mathematical models, it has been shown that it is possible to include in the assessment of insulator performance contamination accumulation that is predicted by using a short historical of chemical components and atmospheric conditions. The results from this work are useful to predict the contamination severity, flashover voltage as a function of contamination severity, leakage current as a function of applied voltage, arc length and contamination severity, and especially to predict the flashover current.     

Investigation of Flashover Performance of Snow-Covered Breakers

When snow is unevenly distributed on horizontal insulators there is a higher risk for flashover. This was investigated for a 400 kV circuit breaker with horizontal breaking chamber insulators. The highest risk occurs when connecting a line to a generator. For a short moment during the synchronization the voltage can reach 2.5 times the normal phase-to-earth voltage. A test method that simulates worst snow conditions in Norway during the synchronization was developed. When simulating these conditions it was possible to construct flashover curves as function of time under voltage. A comparison with the synchronizing voltage made it possible to estimate the risk for flashover during the synchronizing time. There is a very low flashover risk at nominal phase-to-earth voltage. At 25% overvoltage one can expect 50% flashover probability during critical snow condition. A mechanism that shows the interaction of the important flashover factors is presented.     

基于有限元的绝缘子污闪模型计算

为精确模拟模型绝缘子污闪发生过程以探索污闪的机理、建立污闪的预测机制,用静态电场有限元分析法计算了典型模型绝缘子的临界闪络条件、闪络发展中弧长和电流的变化、弧足场强分布及形成系数等参数。比较该计算法、传统分析计算法和实测3种结果表明,有限元法仿真计算模型绝缘子的动态污闪过程和有关特征量可方便地处理表面复杂或表面污秽分布不均匀的模型;比电荷模拟法及电路分析法更适合分析计算绝缘子污闪。     

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