Using rainwear as switching jackets: a reasonable solution forelectric arc exposure

Louisville Gas and Electric, Louisville, KY, USA, has tested numerous types of clothing for worker protection under electric arc exposure situations and discusses the test methods used, along with practical application of the arc thermal protective value and heat attenuation factor results which are being reported by manufacturers of arc-resistant clothing. This paper focuses on the newly discovered and documented feasibility of using flame-resistant (FR) rainwear in high fault current switching applications. This paper includes data and a comparison of several popular rainwear materials in their performance under electrical arc conditions. Some of these rainsuits have been shown by mannequin testing to withstand arcs up to 30 000 A, 15 cycles without sustained fire or ignition of clothing covered. Using rainwear as switching jackets could allow “double-duty” use of rainsuits in plants and on line trucks. Further, Neoprene/Nomex and some PVC/Nomex/Kevlar rainsuits have, in testing, proven more protective than woven Nomex “switching jackets” costing substantially more     

Testing update on protective clothing and equipment for electricarc exposure

Even though significant progress has been made in understanding and quantifying the hazards to personnel from electric arcs, additional testing is required to better estimate the incident energy produced by electric arcs on the many different types of electric power distribution systems. Additional arc testing has indicated that placing a three phase arc in a specific cubic box increased the incident energy by a factor of 3 compared to the same arc exposure in open air. Peak noise levels during the three-phase electric arc tests were found to be at levels sufficient to cause traumatic ear damage. Leather work gloves were found to provide protection for hands exceeding that of a Class 2 FR clothing system, but less than that of a Class 1 FR clothing system. Of all the head protective systems evaluated, hoods with 80 mil gold-coated polycarbonate windows were found to be the most protective     

Minimizing burn injury: electric-arc hazard assessment andpersonnel protection

Significant progress has been made in understanding the arc flash hazard and protecting people. Standard tests have been established to determine the incident energy required to cause ignition of non-FR clothing and evaluate the protective characteristics of FR clothing. One process for selecting FR clothing to protect personnel against arc flash injury has been presented. Protective characteristics for classes of FR clothing and rainwear have been summarized. This performance information is based upon test data produced in a laboratory simulation, not in real-life conditions that may vary. The user is responsible for determining appropriate FR clothing and protective equipment based upon the actual conditions of use and exposure. Incident energy levels produced by three-phase arcs with a 1.25 in electrode gap on a 600 V electrical system with varying bolted fault values have been experimentally determined in a laboratory setting. Algorithms have been developed for predicting incident energy as a function of available bolted fault current, arc duration, and distance from the arc electrodes; and constant incident energy boundary distances     

Comparison of methods for selecting personal protective equipment for arc flash hazards

In 1960, a large global chemical company began documenting and implementing requirements for preventing injuries from electric arc flash hazards, including appropriate personal protective equipment (PPE). Methods evolved from requiring a 100% natural fiber long-sleeve shirt for a specific task to a detailed analysis with multiple flame-resistant clothing options. This paper compares the PPE required by these methods, based on hazards analysis in more than 65 manufacturing and laboratory facilities. The total costs for the example company are estimated for each method.     

IR sightglasses protect against arc-flash exposure

The intense energy and duration of an electric arc flash represents a very unique exposure. Everyday work clothes made from regular cotton or polyester cotton blended fabrics, regardless of weight, can be readily ignited at some exposure level. Once ignited, the clothing will continue to burn, adding to the extent of the injury sustained from the arc alone. The National Fire Protection Association (NFPA 70E) standard for electrical safety requirements for employee workplaces now requires employees to wear flame-resistant (FR) protective clothing wherever there is possible exposure to an electric arc flash. This clothing must meet the requirements of ASTM International, formally known as the American Society for Testingand Materials (ASTM) document reference F1506. It also requires employers to perform a flash hazard analysis to determine the flash protection boundary distance.     

Analytical Method for Coordination of Surge Arresters with Current-Limiting Fuses

Many industrial power systems have lightning exposure, requiring surge (lightning) arresters; dry-type transformers, requiring low protective levels; and high available fault currents, making the use of current-limiting fuses desirable. On occasion, current-limiting fuse arc voltages have resulted in destruction of low characteristic arresters. A traditional guideline has been to select arrester types and ratings that will not spark over on current limiting fuse maximum arc voltage?an approach that may not be entirely viable for industrial systems. A step-by-step analytical approach to the selection of surge arresters for use with current-limiting fuses is presented. The method presumes arrester sparkover and is based on determination of system energy, fuse arc voltage and arrester back voltage characteristics, and arrester energy capability.     

IEEE 1584-2002

IEEE 1584-2002 was developed to help protect people from arc-flash hazard dangers. The predicted arc current and incident energy are used in selecting appropriate overcurrent protective devices and personal protective equipment, as well as defining safe working distance. Since the magnitude of the arc current is inherently linked with the degree of arc hazard, the arc is examined as a circuit parameter. Furthermore, since estimation are often useful, simple equations for predicting ballpark arc current, arc power, and incident energy values and probable ranges are presented in this work.     

Fire-Retardant Cable Systems

The increasing use of nonmetallic cables in cable trays for industrial plant applications as recognized in the 1975 National Electrical Code, Article 340, mandates that these cables be suitable for this application and that the outer sheath be flame-retardant. The significance of various flame tests is discussed, and data obtained following procedures and modifications of IEEE Standard 383-1974, Section 2.5, are presented. It is evident that nonmetallic sheathed tray cables are available that will comply. Furthermore, when a flame-resistant jacket is applied over type ALS, MC, or AC armored assemblies, it results in an exceptionally rugged, corrosion, and flame-resistant nonpropagating construction.     

Design aspects of industrial distribution systems to limit arc flash hazard

Industrial distribution systems have been designed in the USA, considering prevalent standards, i.e., American National Standards Institute (ANSI), IEEE, National Electrical Code (NEC), Occupational Safety and Health Administration (OSHA), etc., and arc flash was not a consideration for designing electrical power systems in the industry. Functionality and economics were the important factors, and will always be so. However, the arc flash analysis and limiting the incident energy will usher a new parameter in system design. It can be demonstrated that in many current installations and new installations designed without considerations of limiting the arc flash energy, the hazard risk category exceeds the highest Class 4 personal protective equipment (PPE), i.e., an arc thermal performance exposure value (ATPV) of 40 cal/cm/sup 2/. This paper discusses typical industrial distribution systems at low-voltage and medium-voltage levels and demonstrates the impact of system design decisions and protection on the incident energy and arc flash hazard reduction.     

The Behavior of Arcing Faults in Low-Voltage Switchboards

An arc fault is the discharge of electricity through the air between two conductors creating large quantities of heat and light. It is widely accepted that there are many variables which affect the behavior of an arc in real switchboards, and thus, understanding the phenomena is difficult. This paper is based upon the results of several years of arc testing with circuits from 155 Vdc to three-phase 450 Vac and at power levels from tens of kilowatts to several megawatts. The goals of the testing were to understand the general behavior of arcing faults in low-voltage switchboards-well enough to predict the motion of arcs-and to design electronic monitoring systems that are capable of protecting switchboards against arcs. This paper will focus on the arc behavior, whereas our other papers will discuss its implications upon forensic investigations and upon the arc-fault protective systems.     

基于电位转移电弧能量的±800 kV直流输电线路等电位进入路径研究

进入等电位极导线是开展±800 kV特高压直流输电线路带电作业的关键环节,优化带电作业人员进出等电位的路径对确保人员的安全具有重要意义。本研究基于电位转移电流及其电弧能量的计算优化进出等电位路径,搭建了电弧能量计算模型,利用有限元(FEM)计算了3种进入导线方式下的人体电位、不同转移距离、悬浮电位人体-极导线的局部电容,分析了不同进出方式下与电位转移电流大小及电弧能量之间的关系。结果表明:从下方进入导线时人体电位最低,此时进行电位转移时的电弧能量在3种进入方式中最大;从上方进入导线时人体电位最高,其电位转移电弧能量最小。该计算方法和结果可供±800 k V直流输电线路带电作业进入路径选取和安全防护用具设计时参考。     

长间隙小电流空气电弧动态特性(英文)

单相接地故障引起的配电网短路电弧和输电网潜供电弧在大气中自由燃炽,电弧的非线性使电弧试验和建模都存在较大的难度.本文对这种长间隙小电流空气电弧的物理特性进行了测试和分析,测量了容性和感性回路产生小电流电弧的电压和电流波形,并拍摄了电弧发展的动态图像,以此分析了电弧特性的时变特征.结合电弧理论和物理学说,详细阐明了电弧电压和电流波形的产生机理及发展轨迹,并给出了电弧的弧道电阻和动态伏安曲线,揭示了电弧各物理参量之间的关系和变化趋势.最后提出了电弧自熄判据,并以此计算了燃弧时间,与实测时间基本吻合.结果表明,长间隙小电流空气电弧特性研究的方法合理、结论可信,对分析电弧自熄特性和建立科学的电弧模型具有参考价值.     

超/特高压架空输电线路短路接地线烧伤分析

通过EMTP仿真计算,分析了淮南—皖南—浙北—上海1 000 kV交流同塔双回线路单回停电时的感应电压和感应电流,结合接地线服役情况,发现停电线路上的感应电压过大,以及接地线挂设过程中存在的反复拉弧放电是造成接地线烧伤的主要原因。利用模拟试验,在计算得到的最大感应电压下,对搭接接地线过程中的电弧进行试验研究,得到电弧能量对导线及工器具影响的临界值,通过引入消弧技术有效地解决了烧伤问题,为输电线路检修人员的作业安全提供了保障。     

CO2气体保护焊在中厚板焊接中的应用

随着国内经济的发展,钢制构件在市场中的需求量也随之迅速增加,各种材质的中厚板及超厚板在钢制构件的制造中,被越来越多的应用,在钢制构件的生产中主要的焊接方法有：焊条电弧焊、CO2气体保护焊和埋弧焊。目前,CO2气体保护焊已被广泛地应用到钢制构件的中厚板的焊接中。从分析CO2气体保护焊的焊接特点着手,探讨了CO2气体保护焊在中厚板焊接中的应用。     

Dynamic modeling of DC arc discharge on ice surfaces

A dynamic model for predicting DC arc behavior and critical flashover voltage of ice-covered insulating surfaces is presented. The model takes into consideration insulating geometry, pre-contamination level, and characteristics of ice layers. Assuming arc behavior as a time dependant impedance, it is possible to determine various arc characteristics such as time histories of leakage currents, potential gradient, channel radius, trajectory, propagation velocity and the energy injected into the zones free of ice (also called air gaps). The simulated results provided by the model are in agreement with those obtained experimentally using a simplified ice-covered cylinder as well as a short string of five IEEE standard porcelain suspension units covered with artificial ice.     

低压配电领域中的故障电弧防护

综述国外近年来在电弧故障防护方面的研究成果。在阐述故障电弧物理现象的基础上,介绍了故障电弧防护标准。在分析了目前常用的几种常规保护线路后指出,它们并不能对故障电弧进行全面保护。分析了故障电弧产生的原因,并给出了防护措施。重点介绍国外几个实用的故障电弧防护系统。最后对我国开展电弧防护技术的工作提出建议。     

低压配电领域中的故障电弧防护(续)

综述国外近年来在电弧故障防护方面的研究成果。在阐述故障电弧物理现象的基础上,介绍了故障电弧防护标准。在分析了目前常用的几种常规保护线路后指出,它们并不能对故障电弧进行全面保护,分析了故障电弧产生的原因,并给出了防护措施。重点介绍国外几个实用的故障电弧防护系统。最后对我国开展电弧防护技术的工作提出建议 。     

基于电弧特性的特高压输电线路单相自适应重合闸

提出了一种基于电弧特性的特高压线路单相自适应重合闸方案。通过EMTP-ATP软件中的MODELS模块建立二次电弧模型，模拟了瞬时故障时二次电弧的反复燃烧-熄灭-重燃的过程。利用数学形态学的多分辨形态学梯度提取故障相母线电压信号的暂态分量，通过比较故障相母线电压谱能量的差异来判别瞬时性与永久性故障。EMTP仿真数据都证明该方案能准确地区分故障类型，可靠地实现自适应重合闸。     

基于新型故障电弧模型的电弧能量特性分析

建筑物低压配电系统中频繁发生的电气火灾现象主要由故障电弧引起。电气火灾发生的频率和严重程度与故障电弧释放能量的大小密切相关。为此,分析了故障电弧引起的电路特征变化,根据该特征建立了能描述发生故障时电弧电路动态变化特征的新型故障电弧时变电阻模型,利用该模型计算了不同负载情况下故障电弧的电压、电流。在此基础上,分析了不同负载条件下故障电弧能量特性,并讨论了故障电弧的能量与负载有功功率、功率因数的关系。研究结果表明,负载有功功率越大、功率因数越小,故障电弧释放的能量越大,越容易引发电气火灾,需要重点进行故障电弧检测与防治。     

基于小波分析信号特征频段能量变比的故障电弧诊断技术研究

为了分析和研究故障电弧的特性,进而快速及时地检测出电弧故障,以便快速切断故障线路,笔者提出一种利用小波变换来分析故障电弧电流特征频段能量变比的诊断方法,通过采用db5小波基函数分别对线路正常工作情况下电流信号和串联型故障电弧电流信号进行6层小波分解,从而提取正常情况下和故障电弧发生情况下的频带能量值及其前后的能量变比,其中d4、d5细节信号所在的频段为故障电弧的特征频带。利用此故障电弧的典型特征可以准确地实现对故障电弧的诊断,且该分析结论对于线性负载情况下的故障电弧诊断研究具有普适应意义。