电缆防蚁问题

交联聚乙烯绝缘电力电缆由于具有良好的电气性能 ,敷设安装相对简单 ,运行维护方便等一系列优点 ,得到广泛使用。但在南方地区电缆外护套遭受白蚁破坏的问题显得日益突出 ,需引起我们的高度重视。白蚁能把电缆护层咬穿 ,使电缆绝缘受潮 ,绝缘电阻下降 ,从而造成单相接地短路 ,使电缆线路发生永久性故障 ,甚至引起爆炸。1　电缆遭受白蚁蛀蚀实例2 0 0 1年 8月 2 3日我公司在 1 1 0kV××线电缆年度试验中 ,发现电缆外护层绝缘电阻明显下降 ,低于电缆正常运行数值。 2 0 0 1年 1 2月 3日开始 ,经测试、寻查并开挖后发现 ,沿电缆路径每隔 2 0m…     

Grounding effects of HV and MV underground cables associated withurban distribution substations

This paper derives a model for the evaluation of the performances of composite grounding systems of urban main distribution substations and associated power cable networks. The effects of the cables upon the dangerous voltages, transferred potentials and ground fault current distribution are encompassed including the conductive and magnetic coupling among grounding system elements, as well as the nonlinearity of cables sheaths impedances. An application example is presented, as are some experimental data     

Examination and location of partial discharge sites in severelyaged underground distribution cables

This paper presents the results of laboratory investigations of partial discharge (PD) in field aged XLPE underground power cables. PD measurements were made on sixty-one cable samples over a three year period. When PD was detected, the magnitude was measured and a site location was determined. PD site locations were predicted using time delay estimations between PD pulses arriving at opposite ends of the test cable. Fourteen of the samples tested had detectable levels of PD. Some of these PD sites extinguished during the measurement period and were returned to rated voltage aging. When samples had continuously active PD sites, they were either dissected or returned to the aging test. Four sites of this type were found allowing two for dissection and two for aging. Seven of the samples failed after PD measurements. All seven failed near the predicted PD location. During the PD testing, no test cables contained PD which initiated at or below operating voltage. When PD detection equipment was monitoring cables which failed, the failures occurred from 2 to 80 minutes after the presence of PD pulses was detected     

基于热电耦合的10kV XLPE地下电缆群温度场数值计算

利用有限元计算了地下电缆的焦耳损耗和温度场分布,利用迭代法实现地下电缆温度场和电磁场间的耦合计算,提高了地下电缆温度场计算的精度,利用迭代法确定地下电缆的载流量。本文对地下直埋多芯电缆群的温度场进行了计算,并给出了相应的载流量。耦合计算结果比非耦合计算结果更接近试验结果,完全满足工程实际的需要。     

Magnetic field management techniques in transmission underground cables

Magnetic field management is concerned with the minimization of the effects of such fields on the public health, without sacrificing the effectiveness or reliability of the power system. The essential management techniques used for the underground transmission cables comprise geometry manipulation phase placement, and source shielding. In this paper, the simulation results of the standard recommended stack, triangular and flat configurations are presented. The simulations have been carried out for single and three phase cables. The resulting fields for different depths have been evaluated and compared. The results led to the conclusion that judicious placement of phases is a very powerful management technique to reduce the magnetic field as cost has not been changed. The appropriate phase placements corresponding to minimal field values are obtained.     

Earthing effects of uncoated underground cables and transferred potentials

Contents A model for the analysis of earthing effects of uncoated metallic sheathed underground cables is suggested. The model includes the proximity effects between the cable sheath and the earth electrodes of the transformer stations at the cable's terminals. Diagrams for assessing apparent sheath impedances to earth as well as transferred potentials and dangerous voltages at terminal stations are constructed appropriate for practical design.

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Wirkung von Erdkabeln mit nichtisolierten Mänteln und die erzeugte Potentialverteilung

Übersicht Ein Modell für die Analyse der Erderwirkung von Kabeln mit nichtisolierten Mänteln wird vorgestellt. Das Modell berücksichtigt die gegenseitigen Beeinflussungen zwischen Kabeln und Erderanlagen an den Kabelenden. Diagramme für die Beurteilung der Erdausbreitungsimpedanzen von Kabeln, der erzeugten Potentialverteilung und Berührungs- und Schrittspannungen entlang der Kabeltrassen werden für die praktische Anwendung angegeben.

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List of symbols J fault current at the HV/MV station flowing into the earth - u _k potential of earthing system elementk - i _k current emanating into the soil from elementk - E _t,E _s touch- and step-voltages - Y longitudinal admittance of a cable sheath segment - Y _n admittance to earth of the earthing structure bonded with the terminal station earth electrode - r _kj mutual earth resistance for elementsk andj - r _kk self resistance to earth of elementk - r _kM mutual earth resistance of elementk and pointM - Z _eq equivalent system impedance to earth as viewed at HV/MV station - Z _a apparent cable's impedance to earth - l(l ₁) cable (characteristic) length - s sheath's segment length - H, d cable's depth of burial and diameter - D diameter of the equivalent plate modeling HV/MV station electrode - l _r,d _r rod length and diameter - earth resistivity     

Factors influencing ampacity and temperature of underground power cables

This paper presents the factors that influence ampacity and temperature rise of three-phase, single-core 33- and 500-kV XLPE underground cables (UGC) using CYMCAP software. These factors are conductor cross-sectional area, soil thermal resistivity, cable burial depth, cable separation, sheath bonding, bedding and backfill heights and thermal conductivities, nearby parallel heat source, formation of dry zone, loss tangent and segmented conductors. Results reveal that increasing the separation distance between phases gives higher ampacity, contrary to the burial depth. The rate of conductor temperature reduction due to the increase in the bedding thermal conductivity is more pronounced than that achieved by increasing backfill thermal conductivity. Furthermore, increasing the native thermal conductivity and/or the maximum conductor temperature increases the UGC ampacity and consequently increases the induced sheath voltage. Sheath losses are significant in transmission UGC where the load currents are always high. High conductor temperature and hence degradation rate is expected for UGC carrying currents of highly fluctuating loads. UGC must be derated as they age (increasing loss tangent), or when dry zones are formed around them, or when a nearby parallel heat source. Finally, it is found that the increase in the number of conductor segments nonlinearly increases the UGC ampacity.     

Evaluation of methods for discrimination of energized underground power cables

The maintenance and repair of underground cable power networks often requires the discrimination of energized cables among a group of unenergized ones. Presently, an invasive detection method is performed which requires utility personnel to puncture the protective cable shielding, creating a potentially hazardous situation. This paper presents a noninvasive approach for energized cable detection based on the electrically induced acoustic waves inside of the cable. The influence of background electric fields on the performance of this approach is studied. In addition, the use of a fiber optic acoustic sensor would significantly increase the safety of the detection procedure, borrowing on the intrinsic electrically insulating properties of optical fibers (i.e. dielectric, immunity to electromagnetic interference, etc.). Feasibility studies and preliminary experiments were performed using a fiber Fabry-Pérot interferometric acoustic sensor. The performance of the fiber optic sensor is compared with that of a piezoelectric accelerometer. A detailed analysis of the test results is included. Recommendations are given for correct interpretation of test results based on the specifics of a power system and sensor type.     

不均匀土壤中电缆集群的优化运行

电力电缆集群在统一的栽流量下运行,未能充分挖掘电缆的输送能力.为提高地下电缆集群的总体输送能力,本文采用基于有限差分法的电缆温度场数值计算程序和人工鱼群优化算法,以电缆群电流之和最大为目标函数,以所有电缆温度低于其最高额定温度为约束条件,确定带回填土的电缆集群每一回路的优化运行电流.计算结果表明,回填土热阻系数较大时,...     

基于馈线组的配网馈线故障集中处理模式

馈线故障自动处理是配电自动化系统的重要功能,该方案介绍一种基于馈线组的配网馈线故障集中处理模式,可克服传统的配网馈线故障集中处理模式下不能针对不同区域情况采用不同的故障处理方式的问题,避免设备故障检测的保护信号调试对馈线故障处理功能的影响。     

Multi-objective feeder reconfiguration by distribution managementsystem

Feeder reconfiguration for use by distribution management systems is discussed in this paper. Multiple objectives are proposed to reflect realistic operating environments while achieving all benefits from feeder reconfiguration. The multiple objectives considered are minimization of power losses, load balancing among supply transformers, minimization of the worst voltage drop, minimization of service interruption frequency, and balanced service of important customers for enhanced service reliability. The objective function containing five different objectives are optimized subject to capacity and protection device constraints. The overall solution approach is a two-stage process. In the first stage, a suboptimal solution is found by analyzing the mesh distribution system in which all open switches are simulated to be closed. Applying special power flow analyses to this mesh network, a radial distribution system is determined as an intermediate solution. In the second stage, this solution is continuously improved by the branch exchange scheme. Special topology models are also developed to accelerate the search procedure. Use of the algorithm is illustrated by numerical examples     

Calculation of thermal fields of underground cables using theboundary element method

The boundary-element method (BEM) is used to solve the underground cable thermal field problem. Because attention is focused on the region boundaries rather than on its interior, the computational effort is reduced very significantly. Examples of application of the BEM include homogeneous soil and multimedia systems. Single and multicable geometries are investigated. The results exhibit accuracy better than can be expected for commonly used domain-type methods, since region truncation with an artificial boundary is not needed     

Multiconductor analysis of underground power transmission systems: EHV AC cables

It is widely ascertained that the multiconductor analysis is a powerful tool which can solve any structurally complex circuit (e.g., high-speed railway supply system, gas insulated lines, etc.). Moreover, this method can be also used as an in-depth analysis of the electric networks after the power-flow studies when they introduce simplifying hypotheses especially in the presence of asymmetry. In this paper, the multiconductor cell analysis has been applied to AC underground cable lines (UGC). This multiconductor procedure based on the use of admittance matrices, which account for the line cells (with earth return currents), different types of sheath bonding, possible multiple circuits, allows predicting the steady-state (and faulty) regime of any cable system. The method calculates the proportion and behavior of the phase currents carried by each parallel conductor, the circulating current in the sheath of each cable and the stray current in the earth. Moreover, some comparisons have been made with traditional programs showing the great accuracy of multiconductor cell model.     

Technical trends of high voltage and large capacity underground power cables

A 275 kV cross‐linked polyethylene (XLPE) cable with a large size conductor is mainly used for large‐capacity underground transmission lines in Japan. Furthermore, 275 kV gas insulated transmission line (GIL), which has a larger transmission capacity than 275 kV XLPE cable, has been developed and is in operation. The achievements regarding high voltage, large capacity underground transmission lines applied by the Chubu Electric Power Company will be introduced. In addition to these technologies, recent technical trends such as Rubber Blocked Joints (RBJ) will be presented. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Robust feeder reconfiguration in radial distribution networks

Distribution feeder reconfiguration has been an active field of research for many years. Some recent theoretical studies have highlighted the importance of smart reconfiguration for the operating conditions of such radial networks. In general, this problem has been tackled using a multi-objective formulation with simplified assumptions, in which the uncertainties related to network components have been neglected by both mathematical models and solution techniques. These simplifications guide searches to apparent optima that may not perform optimally under realistic conditions. To circumvent this problem, we propose a method capable of performing interval computations and consider seasonal variability in load demands to identify robust configurations, which are those that have the best performance in the worst case scenario. Our proposal, named the Interval Multi-objective Evolutionary Algorithm for Distribution Feeder Reconfiguration (IMOEA-DFR), uses interval analysis to perform configuration assessment by considering the uncertainties in the power demanded by customers. Simulations performed in three cases on a 70-busbar system demonstrated the effectiveness of the IMOEA-DFR, which obtained robust configurations that are capable to keep such system working under significant load variations. Moreover, our approach achieved stable configurations that remained feasible over long periods of time not requiring additional reconfigurations. Our results reinforce the need to include load uncertainties when analyzing DFR under realistic conditions.     

地下管线对通信电缆的屏蔽效应计算方法

提出了一种同时考虑感性耦合和阻性耦合时的地下管线对通信电缆的电磁屏蔽模型,以管线节点电流代替管线单元电流进行插值,改进了传统电磁屏蔽效应计算方法,在此基础上,进行了地下管线对地下通信电缆的电磁屏蔽系数计算,探讨了屏蔽保护的规律,计算结果表明,管线粗细和端接阻抗将明显影响屏蔽保护效果。     

Refinements to the Neher-McGrath model for calculating the ampacityof underground cables

The Neher-McGrath method has been widely accepted as an accurate and relatively simple way to calculate the ampacity of underground cables. It is based on a number of assumptions that simplify the mathematics, but at the same time limit the accuracy and scope of the model. Furthermore, the model relies upon correlations that are now dated, because more up-to-date and accurate heat transfer correlations are now available. This paper examines improvements to the Neher-McGrath model in three different areas: a more accurate expression for the mutual heating parameter that accounts for unequal heating among the cables; improved correlations for the thermal resistance of a fluid layer that exists in pipe-type cables and cables installed in ducts; and a more accurate model for the thermal resistance of concrete duct banks with nonsquare cross-sections. Example installations are then considered to illustrate how the incorporation of these changes will affect the ampacity of the installation. The refinements suggested result in a more complex mathematical algorithm and require more computational time, but the changes can result in significantly different ampacity values than the ones provided by the Neher-McGrath model     

通过局放诊断使ENDESA中压电缆的预防性维修最优化

本文介绍ENDESA配电公司的一种中压电缆的局放诊断系统 ,其结果能给出一张局放地图展示沿电缆全长在测试时发生局放的区段 ,局放大小和重复出现的频率。从而与电缆在电网中的功能和重要程度结合后制订一种分轻重缓急的有选择的维修行动以达到预期的目标 :降低维修成本 ,减少故障数目和提高供电质量。     

Analysis of water trees in underground HV cables using the KFUPMmicro-PIXE facility

Scanning with the micro-PIXE technique was employed to analyze water trees in the XLPE insulation of a field-aged underground HV cable. X-ray spectra of bow tie and vented water trees, the inner and outer semiconductive compounds, and an insulation spot free from any water tree were acquired. Simultaneously, two-dimensional elemental distribution profiles across the water trees were also measured. Various trace element impurities were identified in the analyzed spots and their possible sources are suggested. Differences in elemental distribution profiles in the scanned areas were observed and have been discussed on the basis of the mechanism of incorporation of these elements into the insulation. This study demonstrates the effectiveness of the micro-PIXE facility available in this laboratory in analyzing water trees in underground power cables