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     

绝缘地线间隙放电对距离保护影响的研究

首先从理论上分析了绝缘地线间隙放电对距离保护的影响 ,并且用ATP对几种常见的接地距离保护进行了充分的数字仿真 ,最后得出接地距离保护在地线分段带间隙的线路上宜按所有间隙都击穿情况下的阻抗参数进行整定     

Influence of charged droplet cloud on flashover of air gaps for lightning impulse voltage

Transmission lines passing through a mountainous region often are struck by winter lightning. As a result, numerous double-circuit faults occur. Space charge might be responsible for this phenomena. Several investigations on flashover characteristics have been performed focusing on reduction of flashover voltage due to ionic space charge formed by corona discharge. In this paper, flashover characteristics of an air gap within a charged droplet cloud ejected from an airless nozzle using an induction charging method are discussed. The droplets are charged in the range -200 to 200 μC/kg, forming the space-charge density of approximately 13 μC/m³. The flashover voltage and the time lag to flashover were measured when 1.2 × 50 μs lightning impulse voltage applied to a rod-sphere gap is placed within the charged cloud. Flashover voltage for a positive rod increased markedly within a positive charged cloud by increasing the charge-to-mass ratio. The increase of flashover voltage was up to 80 percent in comparison with uncharged droplets. Flashover voltage for the negative rod decreased about 20 percent in the cloud of either polarity. The results show that the presence of charged droplets in the air gaps affects the discharge process significantly.     

绝缘地线间隙放电对距离保护影响的研究

首先从理论上分析了绝缘地线间隙放电对距离保护的影响,并且用ATP对几种常见的接地距离保护进行了充分的数字仿真,最后得出接地距离保护在地线分段带间隙的线路上宜按所有间隙都击穿情况下的阻抗参数进行整定.     

固体继电器虚拟装配系统开发

论述了产品装配模型的特点,讨论了在电气领域引进虚拟现实技术就产品装配过程进行仿真的原理和可行性,分析了开发固体继电器虚拟装配系统面临的主要问题及解决方法,并基于AutoCAD 2000图形平台和ARX开发工具实现了该系统.     

固体继电器虚拟装配系统开发

论述了产品装配模型的特点,讨论了在电气领域引进虚拟现实技术就产品装配过程进行仿真的原理和可行性,分析了开发固体继电器虚拟装配系统面临的主要问题及解决方法,并基于AutoCAD2000图形平台和ARX开发工具实现了该系统。     

一起500kV复合绝缘子操作冲击干耐受电压试验对地闪络事件分析

以±800kV新东直流输电工程新松换流站某500kV交流复合绝缘子操作冲击干耐受电压试验过程中发生的对地闪络事件为背景,以试验现象和试验结果为基础,通过简化试验模型的方式,最终查明试验过程中产生对地闪络现象的根本原因,在未安装试验工装时复合绝缘子均压环对地的操作干耐受电压小于试验电压.探究操作冲击干耐受电压试验时,是否...     

Flashover characteristics of vapor-mist dielectrics under lightning impulse and means to increase the flashover voltage

It has been reported that the flashover voltage of gaseous dielectrics may increase greatly when they are mixed with carbon-halide mist. However, the factors which bring about the increase of the flashover voltage still are not clarified fully. Based on the study on the basic flashover characteristics of vapor-mist dielectrics, the authors have suggested the scarcity of initial electrons as the predominant factor. This paper investigates further the effect of UV light irradiation, flashover characteristics under forced supply of initial electrons, and for lightning impulse superimposed on dc voltage. These results have verified that the scarcity of initial electrons is the decisive factor in increasing the lightning impulse flashover voltage of vapor-mist dielectrics. It is clarified also that the scarcity is attributed principally to: (1) the reduction of effective period (lifetime) of initial electrons, and (2) the suppression of photoelectric emission from electrodes.     

Discover relay design and application problems usingpseudo-transient tests

The authors describe how pseudo-transient tests using commercially available instruments have revealed several relay design problems and application limitations. The test method is briefly described, and the results of several series of tests are discussed as examples of its application. The method is not suitable for fully assessing the performance of relays. Its limitations are discussed. In series compensated transmission lines, or in EHV cable circuits (with high shunt capacitance), where power system signals have a large proportion of nonfundamental frequency components, pseudo-transient tests may be of limited use. Even in such cases, depending on the design of the relay input filters, pseudo-transient tests may provide useful benchmark test results for future routine maintenance tests     

The electrical breakdown characteristics of oil-paper insulationunder steep front impulse voltages

Disconnecting switch operations in gas insulated equipment cause transient voltages with risetimes as steep as 5 to 20 nanoseconds and magnitudes as high as 2.5 pu. There is very little information on the effect of these transients on oil-paper insulated equipment. There have been reports, however of transformer and bushing failures caused by these transients. The electrical breakdown characteristics of oil-paper insulation under steep front impulse were studied in this project, which was co-sponsored by the Canadian Electrical Association and BC Hydro. V ₅₀ (50% breakdown probability voltage) breakdown data was obtained with steep front (10 ns/2500 μs), lightning and switching impulse waveforms. Insulation breakdown voltage vs breakdown time (V-t) data and multiple impulse breakdown data were obtained with the steep front impulse waveform. The V₅₀ results showed that the breakdown strengths were lower for steep front impulses than for lightning impulses. The multiple impulse breakdown results showed that oil-paper insulation breakdown strength can be lower than 100 kV/mm. These results are alarming, since they suggest that oil-paper insulated equipment subjected to steep front transients will fail at voltages below the lightning impulse design level (BIL). The volt-time data had a discontinuity. The breakdown process at risetimes below about 50 ns was different from the breakdown process at risetimes above 50 ns     

Comparative investigation of lightning impulse tests on electrical submersible pump motors

This paper investigates the capability of some samples of electrical submersible pump (ESP) motors to withstand standard basic “lightning” impulse level (BIL) and to get the destructive voltage for all phases. Tests were performed on samples from different ESP vendors and with a voltage rating between 1 kV and 2 kV, to fulfill the lightning impulse standard test requirements. All the tested ESP motors showed a decrease in the terminal impedance between one line and the motor casing with the frequency, i.e. low-pass filter effect for fast transient overvoltages. In addition, all ESP motors passed the standard lightning impulse withstand tests with no significant change in the terminal impedance. Used ESP motor failed at 37 pu of the BIL, while all the new ESP motors failed at much lower level up to 22 pu. This trend is attributed to the better oil infiltration in the used motor during runtime than in the new motor with zero runtime.     

电流互感器饱和引起的保护误动分析及试验方法

近年来．广东省内多个发电厂出现过高压厂用变压器或起动一备用变压器在区外故障时或厂用大容量电动机起动时差动保护误动作的情况。为此．介绍了通过电流互感器伏安特性试验确定其饱和特性的方法．并用试验验证了这种方法的可行性。最后提出了关于避免差动保护因电流互感器饱和而误动的措施。     

The influence of wave front duration of impulse voltage on creeping discharges along aerial insulated wire

In high‐voltage aerial distribution systems, creeping discharges progress along the cable surface from the free end of the binding wire when overvoltages caused by a lightning surge have invaded the central line of an insulated cable. Consequently, various accidents such as punch‐through breakdown, melting, or snapping of a cable, often occur at these systems. In our previous studies, it has been clarified that the lengths and aspects of creeping discharges under a 1.2/50 µ s impulse voltage condition can be markedly affected by changes in the electric field strength on the cable surface. However, lightning impulse surges which may invade the central line of a cable have various wave front durations. This will further complicate creeping discharge phenomena due to lightning. In this paper, we report the influence of the wave front duration on both the lengths and the aspects of the creeping discharges which progress on the cable on application of lightning impulse voltages. It has been shown that the behavior of negative creeping discharges reveals pronounced changes in response to the duration of the wave front of the applied voltage. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(2): 30–38, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10263     

Results of lightning impulse tests for a 275‐kV full GIS substation

This paper describes the outline and results of the lightning impulse tests for a 275‐kV full GIS substation. The behavior of lightning surges is a very important factor for the rational design of substations and low‐voltage and control circuits inside the substations. For the above reason, we carried out lightning impulse tests for a new 275‐kV full GIS substation. In these tests, we measured voltage induced in low‐voltage and control circuits, transient characteristics of grounding grid, injected voltage and current waveforms, and so on. By investigating these data, we confirmed the behavior of lightning surges inside the substation. We also compared simulated waveforms by EMTP analysis with the measured waveforms. The simulated results agreed well with the measured results. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 46–58, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10230     

Critical condition of DC flashover on a circular sector model

In order to find the electrical size which determined the critical condition of flashover, the authors have examined the propagation of the discharge on surface under DC voltage in a new laboratory model which has a continuous and radial current distribution. This model is a vat having a circular sector form of variable angles, radiuses and depths filled by an electrolyte. The obtained results on this model show that for a given resistivity of electrolyte: if the current distribution in the horizontal plane is uniform according to the sector angle, the applied critical voltage and the critical current per unit of angle (1deg) are constant for all sectors of various angles, if the current distribution in the vertical plane is uniform according to the depth, the critical flashover voltage and the critical current per unit of the electrolyte depth (1 mm) are constant for all the depths. These results lead to the critical conditions of flashover to be determined by the current per unit of angle and per unit of electrolyte depth (A/deg/mm)     

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。     

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.