Effects of the metal sheathed cables upon the performances of thedistribution substations grounding systems

A model for the analysis of the performances of the grounding systems of distribution substations in underground cable networks with uncoated metal sheathed cables is suggested. The model derived is utilized to analyze the effects of cable sheaths on the ground fault current distribution, on the potentials transferred to the consumers' substations, and on the touch- and step-voltages that could appear in the cable network area fed from the source substation. Several typical cases are studied, and some general diagrams for assessing the effects of cables on the main grounding system performances are displayed. The proposed model takes into account mutual interaction among cable sheaths and substation ground electrode elements through the soil and the voltage drops along the cable sheaths. The analysis of the typical cases has shown that the metal sheathed cables might considerably affect the grounding system parameters and that, therefore, they must be properly taken into consideration     

Comparative analysisof grounding systems formed by MV cable lines with either uninsulated or insulated metal sheath(s)

It is well known that medium-voltage (MV) paper-insulated cables essentially reduce the potentials appearing during a ground fault in substations located in urban surroundings. This is explained by the fact that these cables usually (normally) have an uncoated metallic sheath. Due to this, MV cable lines leaving a high-voltage/middle-voltage (HV/MV) substation act as long external grounding electrodes and spontaneously form one very large and complex grounding system around this substation. Cables with an insulated metallic sheath however, are progressively being more applied in contemporary power distribution practice. Consequently, the following quite logical question arises: how will a cable with such constructive characteristic influence the general conditions for solving the grounding problem of distribution substations, especially of those working in high-voltage (HV) networks with directly grounded neutral(s)? The analysis performed in this paper shows that, when applied these cables spontaneously form a grounding system which also exhibits excellent grounding performances.     

电缆线路对铁路10kV配电所功率因数的影响

铁路10 kV配电所及其馈出的电力贯通线作为重要的铁路电力设施,为铁路沿线各供电设备提供电源,近年来各铁路集团供电部门正在不断地对年久失修的配电所及电力贯通线路进行更新改造.在进行某铁路集团普速铁路小容量10 kV配电所改造设计中,调查发现该所无功补偿装置多年未投入运行,针对配电所功率因数普遍偏高的问题,调查了该铁路集...     

基于空间矢量复合判断指标的变电站动力电缆漏电检测算法

为提高变电站长段动力电缆漏电监测水平,提出了一种基于空间矢量复合判据的变电站长段动力电缆漏电检测算法。首先对现有方法中无法检测三相漏电故障的问题进行了分析。然后,引入空间矢量的概念,将剩余电流数据转换为空间矢量圆,提出了剩余电流差流、A相漏电流以及空间矢量圆半径变化率3个漏电状态判断指标。并建立了针对电缆不平衡漏电及三相漏电故障的类型判断机制,实现了对长段动力电缆漏电状态及类型的准确检测。最后,通过仿真及江苏电网某500 kV变电站实际数据对所提方法的有效性与优越性进行验证。结果表明,该方法能够准确实现对不平衡漏电故障、故障演变过程以及三相漏电故障的判断,丰富了电缆漏电故障的诊断信息,有效提高了对变电站漏电问题的分析处理效率。     

A Simple Method for Evaluating Ground-Fault Current Transfer at the Transition Station of a Combined Overhead-Cable Line

When a substation is fed by a combined overhead-cable transmission line, a significant part of the ground fault current flows through cable sheaths and is discharged into the soil at the transition station where cables are connected to the overhead line. Such a phenomenon, known as ldquofault application transfer,rdquo may result in high ground potentials at the transition station which may cause shocks and equipment damage. The scope of this paper is to present new analytic formulas which can be used for the direct calculation of the fault current transferred at the transition station and its ground potential rise as well as the substation earth current. The proposed formulas allow evaluating the influence of the main factors to the fault application transfer phenomenon and can be employed, at the preliminary design stage, to easily assess the most appropriate safety conditions to avoid dangerous effects.     

变电站地电位升测试系统的研发及其应用

为研究变电站接地短路或雷击故障造成的地电位升高及对二次设备造成的电磁骚扰,需要对变电站瞬态地电位升和二次设备电缆端口骚扰电压进行测量。根据变电站的测量环境与需求,设计和开发了一套具有高分压比、宽频带,适用于变电站现场复杂电磁环境的变电站地电位升测试系统。测试系统的硬件包括电磁屏蔽箱、独立电源模块、信号采集系统和光纤通信模块。基于Labview开发了测试系统和上位机的数据交互软件,实现了骚扰电压的自动测量和存储。经过专业机构性能检测表明,测试系统的电磁兼容性和测量功能均满足变电站现场使用要求,并在某220 k V变电站现场试验中获得了浪涌电压作用下接地网地电位升和电缆端口骚扰电压波形,证明了测试系统的有效性。     

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     

35kV单芯交联聚乙烯电缆不接地系统单相接地故障仿真分析

葛洲坝水电站根据周边电力负荷的发展情况,在2003年对大江电站两台厂用变进行升级改造,更新后的厂用变35kV电压等级通过单芯交联聚乙烯电缆直接敷设至附近的35kV变电站。本文35kV纯电缆线路单相接地故障,利用ATP—EMTP建立仿真模型,对故障现象进行分析,并给出35kV电缆线路运行改进建议。     

大连城网规划中网架与设备选用原则探讨

为城网改造，结合大连电业局配电网架实际，描述了电缆，架空网2种网架，电缆网几个中心开关站相串接，每个开关站从不同变电所的母线或同一变电所的不同母线取得电源，架空线主网架在不同变电所之间，用2－3个分段形关握手互连。使用环网柜和电缆相结合的方式解决了原有架空网下地问题。根据高可靠性和高互连性的原则，对中低压配电网接线原则做了相关的讨论，并就大连配电网提出了选用设备的一些原则。     

Induced transients in substation cables: measurements and models

An extensive set of switching transient EMI response measurements on several types of substation cables and internal cable wires is described in this paper. Measured and predicted cable/wire current and voltage transients at both air-insulated substations (AIS) and gas-insulated substations (GIS) are presented, for system voltages ranging from 115 kV to 500 kV. The maximum peak-to-peak amplitudes of measured wire transients are found to vary from around 1 A to almost 20 A (current in amperes), and from 0.3 kV to almost 7 kV (voltage in kilovolts). Predictive models for field-driven coupling, as well as for direct-driven coupling via current transformers or capacitively-coupled voltage transformers (CTs/CCVTs), are presented. Model predictions are compared to and validated against measured wire transients     

Safety conditions in manholes in the vicinity of substations

In many cases, the manholes for maintaining various installations including power and telecommunication cables, water-, remote heating-, and gas-pipes are located in a close vicinity of power substations. The paper analyzes the risks of the occurrence of dangerous potential differences within the manhole and on the surrounding ground surface during ground faults in the substation. Possible protective measures are discussed.     

Line Arresters Application in Lightning Protection of High Voltage Substations with Non-standard Configuration

In this paper, application of gapless transmission line arresters (TLAs) in substation lightning protection is analyzed. Deterministic calculations in accordance with IEC 62305 are performed. Substations with non-standard configuration equipped with Gas Insulated Switchgear (GIS), long cables, and a direct cable connecting GIS and power transformer are considered. It is concluded that 220- and 400-kV substations lightning performance can be significantly improved by using TLAs at only one or two overhead line towers in front of the substation. In some cases, TLAs provide better lightning protection of power transformer than surge arresters installed in GIS. Positive effects of TLAs application are noticed both in the case of back-flashovers and in the case of shielding failures. TLAs energy stress increases with the decrease of the system rated voltage. Maximum estimated values in the analyzed substations are below 2.5 and 0.5 kJ/kVr for TLAs installed in 220- and 400-kV systems, respectively.     

变电站电缆防火措施及技术对策

电缆在变电站中起着传输能量和信号的作用,变电站因电缆火灾引发的事故时有发生,本文探讨了变电站电缆的防火措施和变电站工程施工中应注意的问题。     

高速铁路电力电缆不对称接地故障对二次电缆的影响

由于空间走廊和建设成本的限制,新建高速客货共线铁路10 kV供电电缆、通信电缆、信号电缆等二次电缆同沟敷设。这些电缆之间相邻距离近、平行距离远,处于同一电磁环境中的电气线缆通过各种电磁耦合方式彼此紧密联系在一起。通过理论分析、计算机仿真计算等方法,分析高速铁路电力电缆不对称接地故障对通信信号电缆的影响。     

采用MATLAB仿真的变电站高压进线温度场和载流量数值计算

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。     

变电站内的电磁干扰及电磁兼容问题

变电站是一二次设备最集中的场所,系统运行方式的改变,开关的动作,雷电流的出现以及二次电缆间的电磁耦合都会对二次回路产生干扰,特别是引进微机监控和保护设备后,电磁干扰问题更不容忽视。海南省几个变电站改造,采用在互感器原、副绕组间装设屏蔽层,加装浪涌吸收器,采用多层电缆并将电缆外皮多点接地,以及对控制室信号线和计算机室进行屏蔽等抗电磁干扰措施后,收到了良好的效果。     

Real time prelocalization of underground single-phase cable insulation failure by using the sheath behavior at fault point

This article presents a prelocalization approach of insulation faults affecting single-phase cables by using electrical measurements of voltage and current available in one substation. This approach is based on the theory of distributed parameters for modeling the faults to the ground. The specificity of this approach is the introduction of a resistance modeling the sheath-ground insulation allowing us to study the various types of faults to the ground (frankly and resistive). The fault distance and resistances are determined by two methods numerical and analytical. Many fault scenarios applied to the 150 kV underground cable connecting HTB sub-stations of Tyna-Taparoura-Sidimansour in Sfax, show a good agreement between the two methods. A simulation of the global system using the software Simulink-SimPowerSystems of Matlab is carried out giving us the voltages and currents on the source side necessary to the execution of the developed methods and the validation of the obtained results.     

旧变电站电缆混放的改造方法介绍

旧变电站经过多年的运行和更动,无论电力电缆或控制电缆都十分凌乱,是旧变电站改造工程的一项十分困难的工作。凌乱的电缆对运行安全威胁极大,必须理顺。这里介绍惠州220kV湖滨变电站电缆改造成功的经验,供同行参考。     

变电站电缆通道多参量采集和预警技术研究

针对变电站电缆通道数量的不断增加,电缆分布众多,某条线路的故障会带来极大的安全隐患。文中提出一种变电站电缆通道多参量采集和预警系统的设计方案,重点研究电力电缆的温度场和载流量。通过有限元分析软件,建立了10 kV单芯电缆四回路标准敷设电缆沟的几何模型,并采用割线法计算稳态载流量。通过实验分析了不同工况下的温度场和载流量。结果表明,对于在线电缆温度监测,只需要对温度最高的电缆进行监测,电缆铺设密度过高会导致电缆的载流量下降。该研究为中国变电站电缆通道多参量采集和预警技术的发展提供一定的参考和借鉴。     

Analysis of ground fault current distribution along nonuniform multi-section lines

In case of a substation supplied by a combined overhead-cable line, most of the ground fault current flows through the cable sheaths and discharges into the soil surrounding the point of discontinuity, where cables are connected to the overhead line. In the paper a new method is presented for computing the ground fault current distribution in case of feeding line consisting of two or more different sections, i.e. part overhead and part underground cable. Besides the calculation of the earth current at the fault location, the leakage current at the transit/transition stations as well as at the overhead line towers can be evaluated, in order to ensure proper safety conditions. Based on the two-port theory, the method allows to take into account all the relevant conductively and inductively coupled parameters which take part to the fault current distribution. A computer program based on the proposed method has been developed and some application examples are reported.