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A modern large polyethylene plant requires a sophisticated electrical power supply to meet the requirements of a continuous process industry. The principal features of such an electrical power system are summarized. The power system was designed to achieve project objectives which stressed safety of operation, ease of maintenance, and high reliability. Some of the modern design features discussed are dual 230-kV power supply lines; low-profile 230-kV bus work; personnel safety grounding of main substation to reduce step and touch potential to safe levels; transfer trip signals to utilize the utility company's switching equipment; extensive protective devices to detect and initiate switching equipment action for power equipment malfunctions or power system faults; vacuum switched under-load tap changers on main power transformers; vacuum breakers for 13.8-kV switching equipment; climate-controlled elevated substation buildings to permit bottom entrance and exit with all power and control cables; nonmetallic sheathed power and control cables in open cable tray; medium resistance ground derived by zig-zag grounding transformers in the 13.8-kV distribution system; high-resistance grounding at the secondary wye connection of all 4. 相似文献
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The existing code for ampacity of cables in a tray does not account for load diversity among the cables and it does not consider the presence of tray covers. This paper provides two factors that can be used to determine ampacity values for these two cases. These factors can be used in conjunction with existing code ampacity values so that cable ampacities can be calculated for diversely loaded, covered and uncovered trays. Also, the case of a few heavily loaded cables in an otherwise lightly loaded tray is addressed. This particular situation can produce nonconservative ampacity values if treated with a one-dimensional heat transfer model. The problem of both load diversity, and the presence of a cover are addressed with a computer code that has been described in previous papers. The computer model is designed to provide conservative ampacity values by assuming that the more highly-loaded cables are placed along the tray centerline and the lightly-loaded cables are positioned on the outer surfaces of the cable bundle. In this way the heavily-loaded cables are insulated from the environment and thus the program calculates a conservative cable temperature. The factors that account for load diversity show that a small percentage of cables in the tray can be loaded significantly beyond the code allowable ampacity value if the remainder of the cables are lightly loaded or unenergized. On the other hand, the code-allowable ampacity must be reduced by up to 25% when a solid cover is placed over the tray 相似文献
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Neal T.E. Bingham A.H. Doughty R.L. 《Industry Applications, IEEE Transactions on》1997,33(4):1041-1054
Since 1982, when R. Lee wrote (see ibid., vol.IA-18, p.246), industrial and utility engineers have been attempting to better quantify the degree of risk to personnel associated with electric arc exposure and the appropriate protective clothing to wear to mitigate serious injury. Activity by OSHA, NFPA 70E, and ASTM F-18 has further emphasized the need to protect workers from arc flash burn injuries. This paper discusses the results of multiphase arc testing which has enhanced knowledge about potential arc energy as a function of prospective fault current and arc protective clothing designs that are suitable for different levels of incident arc energy. Incident energy levels are correlated with second-degree burn criteria for unprotected human skin, protective clothing systems consisting of flame-resistant outer layers in single-layer and multiple-layer construction, as well as combination systems of flame-resistant outer layers with natural and man-made fiber inner layers are discussed. Protection recommendations for the face, head, hands, and feet are also included 相似文献
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我国发展直流海底电力电缆的前景 总被引:3,自引:0,他引:3
例举世界重要的海底电缆工程,表明其中大部分为直流海底电缆工程。叙述直流输电特点,着重以不同类型的直流和交流海缆载流量计算,证明直流海底电缆在输电容量、输电损耗和电缆线路长度限制方面显著优于交流海底电缆。肯定了我国发展直流海底电缆的必要性。有些运行条件下直流海底电缆会是优先的方案,甚至是唯一的选择。提出以发展直流交联聚乙烯(XLPE)海底电缆作为主要目标,并在比较不同类型海缆绝缘中的空间电荷对电场分布和电气绝缘性能影响和深入研究空间电荷积聚、抑制和移去机理基础上,积极研发抑制空间电荷积聚的XLPE绝缘料,作为关键技术突破,用于开发直流XLPE绝缘海底电缆,推进我国直流海底电力电缆的技术发展。 相似文献
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采用MATLAB仿真的变电站高压进线温度场和载流量数值计算 总被引:1,自引:0,他引:1
随着电力电缆在输配电线路中的广泛应用,准确确定电力电缆及其周围环境温度场的分布和电缆的载流量对于提高电力电缆的使用率、动态调整负荷具有重要的意义。为此,以地下排管敷设的交联聚乙烯电力电缆为研究对象,其实际模型为1个容量为250MVA、额定电压为230kV的变电站的高压进线。根据传热学和有限元法(finite element method,FEM)基本原理,建立了1种基于有限元法的水泥排管敷设电缆温度场计算模型,并对电缆及其周围环境的求解区域进行复合有限三角形单元剖分,即对电缆区域进行较密集的网格划分,而对电缆周围的土壤区域则进行较为稀疏的网格划分,以提高程序的运算精度和运行速度。结果表明:用MATLAB软件仿真,从而得到电缆及其周围环境的温度场分布,迭代计算了排管敷设交联聚乙烯电缆的载流量。证明使用有限元的方法分析地下电缆温度场,为电力工程中电缆载流量确定提供了一个比较可靠的计算方法。 相似文献
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电缆排管敷设设计之初就考虑到了通过增加电缆回路满足后期增容要求。电缆原始及新增位置不同时,断面温度场和载流量也不同,故有必要对电缆原始及新增位置进行优化。以3×4排管敷设配电电缆为例,建立温度场有限元模型,对比温升试验与有限元计算结果,验证了有限元模型的有效性;基于该模型,在各回路加载相同电流前提下,以发热最严重电缆线芯温度最低为依据,对原始6回路及新增1回路进行位置优化。仿真研究表明,电缆分布越分散温度场分布越均匀,发热最严重电缆线芯温度越低;最优新增电缆位置与原电缆位置有关,因而建议在电缆位置优化时应考虑后期电缆回路的增加。 相似文献
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This paper reviews rating of cables installed in air. The following cable installations are investigated: (1) cables on riser poles, (2) cables in open and closed trays, (3) cables wrapped in fire protection covers, (4) cables in horizontal tunnels, and (5) cables in vertical shafts. The rating of cables in these installations is computed by solving energy balance equations for the unknown surface temperature with a given conductor current. In ampacity computations the conductor current is adjusted iteratively until permissible cable conductor and surface temperatures are achieved. It is shown in the paper how the same energy balance equations can be used to compute the ratings of all the above cable installations 相似文献
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火电厂电气监控系统接入DCS方式的分析 总被引:6,自引:1,他引:5
分析了火电厂电气监控系统(ECS)接入集散控制系统(DCS)的3种模式:硬接线、硬接线+通信、全通信,探讨了不同模式的优缺点和应用中存在的问题,认为硬接线+通信方式是目前火电厂ECS接入DCS的主流解决方案,大大提高了ECS的自动化水平,但目前在应用中还存在ECS与DCS的通信受限、ECS的电气维护和管理功能不十分完善等问题,通过技术的改进、参与各方的密切配合,相信这些问题会很好地得到解决,随着通信技术的日趋成熟和稳定,完全取消硬接线的全通信方式也一定会逐步得到推广。 相似文献
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高温超导电缆在城市地下输电系统应用的可行性研究 总被引:1,自引:1,他引:1
大城市有可能最先采用商业化运行高温超导电缆 ,用于城市地下交流输电系统。其主要应用目标是用于地下电缆工程改造 ,利用现有排管以高温超导电缆取代现有的常导电缆 ,增加地下电缆传输容量以及采用高温超导电缆将巨大电能 (1GVA以上 )输入到城市负荷中心。采用常导电力电缆传输 1GVA以上的电能进入中心城区 ,输电电压一般要求为 5 0 0 k V。在城市中心区不可能建设 5 0 0 k V变电站。 5 0 0 k V电缆线路所需的 5 0 0 k V大长度电缆和相应附件 ,目前尚未研制开发。采用高温超导电缆将有可能降低输电电压等级 ,可以采用 2 2 0 k V高温超导电缆将 1GVA以上的电能输入到城市负荷中心 ,满足特大型城市负荷中心供电需求。采用 110 k V高温超导电缆 ,亦有可能传输 1GVA左右电能。本文通过对交流高温超导电缆系列设计计算对额定电压 35 k V、110 k V、2 2 0 k V的高温超导电缆 ,按不同传输电流 (或传输容量 ) ,以高温超导电缆的传输效率 (损耗与传输容量比 )、高温超导电缆外径限值和超导导体绕制结构限制条件 ,确定高温超导电缆适用性界定条件 ,提出城市地下输电、配电系统用高温超导电缆可行方案。 相似文献
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高压电缆护层交叉互联时的行波故障测距 总被引:2,自引:1,他引:1
为研究采用三相护层交叉互联方式的高压电缆线路的行波测距方法,讨论了裸露高压电缆(电缆沟或隧道敷设)的相量参数和模量参数的计算方法。通过分析模量参数的特征,将电缆中的模量分为内模量和外模量,分别计算了直埋电缆和裸露电缆的内、外模量波速,计算表明裸露电缆的外模量波速高于内模量。电缆护层交叉互联时,内、外模量会因行波折反射而相互转化,波速较快的外模量会对内模量波头造成干扰,给裸露电缆的双端行波测距造成影响。理论分析和数值计算表明,采用三相芯线电流之和作为行波测距信号,可有效消除外模量干扰,大大加强内模量波头特征,有利于提高行波测距准确度。 相似文献
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MOST electrical engineers are aware of the vulnerability of above grade cables to fire and other hazards that could exist, and they are concerned about methods of protecting these cables from such dangers. The intent of underground methods is to provide protection for long cable runs from possible hazards created by nearby units. Other methods can be used within segments of an operating unit where the cables come above grade. 相似文献
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Underground transmission cables are a vital part of any power transmission system which means that the selection of a particular cable must be based upon many considerations ranging from the cost of losses to environmental concerns. The focus of this paper is on the design, selection and testing of power transmission cables within specific geographic regions. Design considerations on a regional basis includes temperature constraints, voltage and voltage stress limits, capacity and ampacity, backfill requirements, cooling and bonding. The material presented in this paper covers land based transmission cables only. Submarine cables, URD or UD cables are not included 相似文献
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A mathematical thermal model is developed to predict the operating temperatures of cables in a single covered tray when there is load diversity in the power cable bundle. The model accommodates two different loading scenarios: one in which the heat is distributed evenly across the cable tray cross section; and one which concentrates the heavily loaded cables along the centerline, while surrounding them with more lightly loaded cables. The temperature predictions provided by the model are compared to data found in other IEEE papers, data collected in laboratory measurements, and new data from a four-year study of cable trays in an operating nuclear plant. Reasons for differences between the field data and the computer results are discussed. The model is used to evaluate the conservatism in the available Codes and Standards. A derating factor is introduced that is defined in terms of the ampacity of power cables in open-top trays. The derating factor accounts for the added thermal resistance present when a cover is placed over the cables, trapping a layer of stagnant air on top of the cable mass. The computer model is then used to predict values for the derating factor as a function of cable depth. The derating factor is shown to be independent of the composition of cables in the tray. The presence of a cover is shown to reduce the ampacity based on an uncovered tray by up to 25 percent depending on the depth of the cables in the tray 相似文献