The Reality of High-Resistance Grounding

In recognition of the successful applications of high-resistance grounding of industrial power systems primarily in the continuous process industries, an attempt is made to identify the broad application areas as well as to offer qualifications regarding the application of the high-resistance grounding concept. High-resistance grounding (arranged to alarm only) has proven to be a viable grounding mode for 600-V and S-kV systems with an inherent total system charging current to ground (3 Ico) of about 5.5 A or less. Beyond this current limit and in applications at 13.8 kV, high-resistance grounding appears to require direct tripping to prevent fault escalation prior to fault locating and removal. The original objective-avoidance of unscheduled shutdowns- could not be realized. The subsequent solution of direct tripping, rather than alarming only, is shown to result in a grounding scheme which is considered to be subordinate to the low-resistance (about 400 A) grounding scheme. In discussing the probable failure mode of motor windings, it is suggested that a ground fault in a motor winding, operating on a high-resistance grounded system, may be caused by an escalated turn-to-turn insulation failure. An indefinite prolongation of the resultant ground fault is likely to result in a further escalation to a phase-to-phase fault which increases the probability of unscheduled shutdowns and excessive motor damage. A precautionary note is included regarding the effect of static conversion equipment on high-resistance grounding.     

High-Resistance Grounding in the Cement Industry?A User's Experience

The use of properly applied high-resistance grounding, with a method of tracing and locating the first fault, offers many advantages to the electrical power system including suppression of transient overvoltages, continued operation on the first ground fault, fast tracing of the first ground fault, and minimizing flash hazard. These benefits along with first-hand experience with a 480-V distribution system are discussed.     

中性点经高阻接地10kV配电网的故障选线

分析了中性点经高阻电网发生单相接地时的故障特性.基于电力系统发生故障后产生的信号具有奇异性、变化较快的特点,而利用小波分析此类信号有较大优势,提出了一种新判据:先求所有出线零序电流幅频特性的最大值,选取幅值特性最大值出线作为准故障线路,再利用小波包对各线路零序电流进行五层分解,对比某节点内的相位,可较准确地选出故障线路...     

10 kV配电网经高阻接地方式下过电压及接地故障选线

针对电容电流<10A的10kV配电网,分析了中性点高阻接地方式的优缺点和阻值选择,对高阻接地方式的过电压抑制效果和单相接地故障选线进行了仿真研究。在河北省张家口供电公司实施了中性点高阻接地方式,并开展了人工单相接地试验。仿真分析、现场试验以及装置运行情况表明,中性点经1200Ω高阻接地方式下,能够实现有效过电压抑制和单相接地故障过渡电阻<3000Ω情况的准确选线。     

考虑地表高阻层的直流接地极跨步电压限值计算方法

为保证直流接地极附近人身安全,接地设计时必须满足跨步电压限值要求。针对水平双圆环形直流接地极,考虑在接地极上方地表铺设高阻层,研究在此条件下跨步电压限值的计算方法,并给出了新计算公式,最后基于边界元法对不同土壤条件下的直流接地参数进行研究分析。研究结果表明：直流接地极地表铺设高阻层能够有效提高人体耐受的跨步电压限值,建议铺设厚度为0.1~0.2 m;为明显提高跨步电压限值,选取的高阻层电阻率最好大于1 000 Ω·m。研究结果还表明,铺设高阻层对直流接地极的接地电阻、地电位升、地面跨步电压以及泄漏电流的分布影响很小,对金属设施的影响也基本可以忽略。     

变压器铁芯高阻接地对绕组电容量和介损测试影响分析

针对一起现场变压器例行试验中出现电容量和介质损耗(介损)数据异常案例,结合测试原理以及变压器的结构设计,建立等效RC电路模型进行仿真分析,研究了变压器铁芯高阻接地对变压器绕组电容量和介损测量影响的规律,并解释了电容量和介损数据出现异常的原因。研究表明,铁芯高阻接地时,会引起各绕组现场实测的电容量和介损数据异常,随着接地电阻值增加,实测电容值略微减少,而介损数据会剧增;铁芯高阻接地对各绕组现场实测的电容量和介损数据的影响程度还与被试绕组自身真实电容量密切相关,被试绕组自身真实电容量越大,其实测的电容量和介损数据受到铁芯高阻接地的影响也越大。     

中性点不接地或高阻接地系统接地故障定位方法探究

本文提出了一种中性点不接地或高阻接地系统接地故障定位的新方法.该方法采 用相对电压算法原理,将数字继电器、零序信号发生器和远距离接地故障指示器相结合,能 处理间歇性故障和多重故障的问题,能识别反向接地故障。     

Charging Current Data for Guesswork-Free Design of High-Resistance Grounded Systems

The design of high-resistance grounded power systems requires the sizing of the grounding resistor to provide a current flow equal to or greater than three times the system charging current (Ico) of each phase. In industrial power systems the insulated power cables are a major source of system charging current which flows into line-to-ground faults. Data are presented which will allow cable charging currents to be quickly and precisely determined after the cable size, voltage, footage, insulation type, and thickness have been determined. Charging current data for transformers, motors, generators, and capacitors are also included.     

变电站接地网不同接地材料接地特性研究

针对电力系统变电站接地网现行的铜、钢以及铜包钢等金属接地材料接地特性的不同,对比分析了铜、钢及铜包钢接地材料的使用成本及腐蚀特性。通过计算对比分析不同土壤条件和不同接地面积下,铜、钢及铜包钢接地网的接地电阻、网内电位差、接触电压以及跨步电压的不同特征。本文所做工作为变电站接地网的材料选择及优化改造提供参考。     

接地电阻测量与三维地网

许多发、变电站建在山区或者周边环境比较恶劣,所处位置的土壤电阻率比较大,即便是建在城市中的发、变电站也要受到占地面积的限制。因此如何在这些高土壤电阻率、扩张裕度有限的地区,使发、变电站地网满足设计规范标准,以确保人身及设备的安全,则是人们所关心的问题。首先需要准确测量接地电阻的大小,测量接地电阻的方法很多,通过分析接地电阻测量的基本原理,探讨理想接地球体状况下的三极直线法（0．618法）和三极三角形法（30°夹角法）,对类似接地工程的设计、施工及测量具有一定的参考价值和借鉴作用。实践表明：增设垂直接地体,采用三维立体接地网（文中简称三维地网）新技术,对于降低接地网接地电阻、减小接触电压和跨步电压是一项行之有效的措施。     

大型变电站接地网接地阻抗与接地电阻的差异

采用基于场路结合方法开发的接地网接地参数数值计算软件分析了接地网的接地阻抗与接地电阻的差 异。计算结果表明:接地电阻的概念只适用于小型接地网;随着接地网占地面积的加大以及土壤电阻率的降低,接地阻抗中感性分量的作用越来越大,大型地网应采用接地阻抗设计。     

斜置接地体对地网接地电阻的影响分析

利用平均电位法对单根斜置接地体和多根斜置接地体的接地电阻公式进行推导。单根接地体的接地电阻随着倾斜的角度增加而增大。水平地网的四角增加接地极后,接地电阻明显降低;纵向接地极的倾斜角度与地网接地电阻有很大关系,且倾斜角度为30°到60°之间时接地电阻较小,相差不大。文章从理论上证明斜接地极法的可行性,得出的结论在变电站接地降阻工程中具有实际意义。     

实用的多根接地电极的接地电阻计算

介绍了改进线电流法,计算出单根垂直接地电极较为准确的接地电阻值.引入相似比和耦合电阻的概念,得到标准双棒形接地电极耦合电阻曲线.并在此基础上推导出多根电极在不同排列方式下的接地电阻计算公式,可以满足工程实际要求.     

伸长接地体冲击接地电阻计算

为较准确解决伸长接地体冲击接地电阻的计算问题 ,采用非线性差分电路模型 ,导出了一种考虑土壤火花放电特性的伸长接地体冲击接地电阻的计算方法。利用该法求得了伸长接地体冲击接地电阻与雷电流幅值及接地体长度的一组关系 ,计算结果与国家电力行业标准及现场试验结果接近 ,可供工程实际参考     

Online Detection of High-Resistance Connections in the Incoming Electrical Circuit for Induction Motors

A high-resistance (R) connection in an induction-motor electrical circuit results in localized overheating and supply-voltage unbalance, which leads to a decreased efficiency and reliability and an increased fire hazard in the electrical distribution system and motor. Therefore, it is important to monitor and correct high-R connections for a reliable, efficient, and safe operation of the industrial facility. This paper focuses on the development of an online technique for detecting poor connections based on monitoring the asymmetry in the voltage and current measurement. The development of the technique begins with the derivation of the dynamic model of an induction motor with high-R connections. Based on the analysis of the model, two approaches for detecting poor contacts using the negative-sequence current and zero-sequence voltage are proposed. In addition to detecting the existence of faults, the location and severity of the fault can also be determined using the proposed method. An experimental study on a 10-hp induction machine under simulated and realistic high-R conditions shows that the proposed techniques provide a simple low-cost solution for reliably detecting poor contact problems at an early stage. It is also shown that the severity and location of the high-R contact fault can be assessed with high accuracy.      

基于小电流灵活接地的单相接地处理

为了更好地利用中性点不接地和经消弧线圈接地的运行优点,更好地应对电力系统发生的单相接地故障,提出一种基于小电流灵活接地方式的单相接地故障处理及控制方法.通过开关控制消弧线圈的投切完成系统中性点不接地方式和经消弧线圈接地方式之间的转换,系统正常运行时消弧线圈为断开状态,若系统发生单相接地故障,迅速采集故障零序信号后,马上...     

斜接地极对改善接地网接地性能作的作用

通过比较对接地网增加不同形式接地极的效果,分析了斜接地极对改善接地网接地性能的作用及其优点,并通过工程实例进行了验证.斜接地极不仅可以起到深井接地极的作用,在无需征地的情况下还可以起到等效扩大接地网面积的作用,且斜接地极相互之间的屏蔽作用比垂直接地极的屏蔽作用小得多,因而在均匀土壤中使用斜接地极比使用相同长度的垂直接地极更有效.当深层土壤电阻率高于表层土壤电阻率时,使用斜接地极的均压降阻效果更佳.     

引外接地对降低接地网接地阻抗的作用

采用接地网工频接地参数分析软件,计算了引外接地网对降低主接地网接地阻抗的作用。计算结果表明,随着辅助接地网与主接地网之间的距离的增加,辅助接地网的作用逐渐减小;并且在土壤电阻率较高的地区,引外接地具有较好的降低主接地网接地阻抗的作用。     

引外接地对降低接地网接地阻抗的作用分析

工程上常采用引外接地的措施,一般根据经验在离主接地网1~2km范围内另敷设一辅助接地网,并采用扁钢将此辅助接地网与主接地网相连,但国内现行接地设计方法及故障电流下地网等电位计算模型均不能计算引外接地电阻。为此采用接地网工频接地参数分析软件,计算了均匀土壤中引外接地网对降低主接地网接地阻抗的作用。结果表明,辅助接地网与主接地网间的距离超过一定数值后,辅助接地网的作用可忽略,且在土壤电阻率较高的地区,引外接地具有较好的降阻作用。