智能接地配电系统

为了发挥中性点非有效接地配电网供电可靠性高的优越性,提出了一种通过在变电站配置智能接地装置并在馈线配置具有零序保护功能的配电终端和故障指示器,将配电网升级为智能接地配电系统的方法。发生单相接地时,智能接地装置可以迅速将故障相短暂金属性接地从而可靠熄灭电弧。若为永久性接地故障,随后控制中性点短暂投入中电阻以显著增大接地点上游的零序电流并基于配电终端和故障指示器处配置的零序电流保护可靠地实现单相接地选线、定位和隔离。论述了智能接地配电系统的组成和关键技术,重点论述了通过电阻分级开关应对选相错误并抑制开关操作引起的系统暂态过程的方法。结合实例论证了所建议的方法的可行性和有效性。     

Losses in electrical power systems

This paper explains the losses in an electric power system. Methods of evaluation of losses in generation, transmission, distribution and consumption are introduced. An understanding of the power system losses is important not only to the power system engineer but also to the energy policy maker.     

关于正确使用携带型短路接地线的探讨

介绍了黑龙江省电力系统接地线使用的状况。对短路接地线允许电流值进行了理论计算，分析了保护动作时间对不同截面积短路接地线允许电流的影响。通过电网运行数据与计算数据的对比分析，提出了具有操作性的建议，可引导技术人员正确选择和使用接地线，确保人身和设备安全。     

A probabilistic method for the design of power grounding systems

An improved multivariable, probabilistic method for the safety analysis of power grounding systems is presented. The application of this method is demonstrated in four examples. The first three examples illustrate the practical evaluation of one new and two existing substation grounding grids when the substation is connected to an overhead distribution system. The fourth example ascertains the relative impact of a difference between the S curve of IEC Publication 479 and Dalziel's equation for the allowable body current used in ANSI/IEEE Std 80-1986 on the validity of an exposure model based on the requirements of Std 80. In this example, the statistical data on ground faults have been taken from actual system records. Further possible refinements of the exposure model are discussed     

变电站接地电网的研究综述

介绍了变电站接地电网的研究动态,对目前该研究领域中的热点问题一接地参数的计算、接地电阻的测量及其接地网的降阻处理等问题进行了分析。运用现代人工智能方法和信息处理技术提高接地电阻测量的准确性和实用性,开发研制降阻效率高、抗腐蚀性好的新型降阻材料将成为接地网降阻的研究方向。     

Phase-shift control of transients in electrical power systems

Phase-shift control is considered to be a useful means of improving the dynamic stability of electrical transmissions with automatic reclosing and of synchronous motors with two excitation windings. The technique ameliorates the restart conditions of large synchronous motors being energized with emergency supply, and enhances the control of the intersystem power flow due to ‘weak’ interconnections. The paper presents the results of theoretical and experimental investigations related to these problems.     

Reliability evaluation of electrical power systems including multi-state considerations

A new approach is introduced for calculating the electrical network reliability indices, such as multi-state stationary availability, expected multi-state capacity, expected unsupplied demand, loss of load probability and total failed system probability. The universal moment generating function approach (UMGF) is used to evaluate the different reliability indices of the power system. In this paper we present a survey of recent work which treats the more sophisticated and realistic models in which components and systems may comprise many states ranging from perfect-working to complete failure. Such systems are multi-state (MSS) as they can have different levels of output performance. The objective is to determine the power structure which minimizes costs and satisfies reliability levels. A computer program has been developed to implement the UMGF technique, and an illustrative example is presented.     

Quick evaluation of voltage surge in electrical power systems

The lattice diagram has been widely recognized and adopted to analyze the voltage surges produced at a particular location in an electrical system. These transient surges are caused by traveling waves induced by lightning strokes or switching operations. A lattice diagram can be used effectively, but the required computations are tedious. A simplified approach based on mathematical derivation is presented. The method will permit a quick evaluation of both initial and crest surge magnitudes as well as a wave shape that are all based on a given incoming surge and the surge impedances of the electrical elements involved. Sample calculations from the lattice diagram and the proposed quick evaluation are compared     

Quasiperiodic (QP) oscillations in electrical power systems

The occurrence of quasiperiodic (QP) oscillations in power systems, a phenomena hitherto unknown, was first experienced in the French grid when attempting to energize an unloaded transformer at the end of a long transmission line. There are no simple analytical tools available to study conditions for the occurrence of QP oscillations. In this paper, the conditions necessary for the occurrence of quasiperiodicity are shown by solving the system equations using the method of harmonic balance. It is shown that QP oscillations will occur due to the severity of magnetizing nonlinearity of the transformer core. It is also shown that if core losses are high, only frequency locked oscillations can occur. The results are confirmed by numerical solution on the original set of differential equations.     

Fault location in electrical power systems using intelligentsystems techniques

In this work an artificial neural network based methodology is proposed for power systems fault location. Several artificial neural networks are employed, each of them being responsible for detecting faults involving a limited number of components. The proposed methodology is tested using a test system and a real Brazilian system. Indexes based on the Hamming distance are also proposed for feature selection and analysis     

Life extension for electrical power distribution systems usingvacuum technology

Three alternatives for upgrading old equipment are discussed. Retrofitting with vacuum arc interrupter technology is the most cost effective and offers many advantages over older air-magnetic interrupters. These include simpler design, fewer parts and less maintenance, readily available parts, high reliability, extended insulation life and safety. The authors address modernization options available to industry specifically in the area of electrical switchgear. Emphasis is given to switchgear life extension using vacuum technology, its benefits, reliability, and economic justification. Several examples and applications are presented     

Dynamic equivalents for transient stability studies of electrical power systems

Along with the growth in size of electrical power systems, attention is increasingly being given to various reduction techniques of dynamic system models for transient stability studies. One of these is the topological reduction that includes coherency-based aggregation. A theorem from the nonlinear vibrations theory is applied to derive analytical coherency-criteria for a classical model of the system. A simplified algorithm of coherency recognition is given and results for a sample system are shown. Important properties of topological equivalents are proved and a relationship to modal reduction is pointed out.     

小电流接地电网单相接地故障的小波选线方法

中性点非有效接地配电网发生单相接地故障时 ,尽快选出故障线路对电网运行有重要意义 ,但选线问题迄今尚未能很好解决。在分析了小电流接地电网发生单相接地时暂态特征的基础上 ,提出应用小波变换提取故障暂态信息 ,实现故障选线的方法。由于利用暂态量 ,该方法适应性、灵敏性均优于现有的基于稳态量方法。     

特高压和高压直流输电系统共用接地极模式分析

为了节省占地面积和建设费用,云广特高压直流输电系统和贵广二回高压直流输电系统在广东侧决定采用共用接地极模式。讨论了特高压和高压输电系统的共用接地极模式,对共用接地极的要求提出了设计方案。分析了共用接地极对2个直流输电系统的稳态运行、过电压绝缘配合以及控制保护系统的影响。结果表明:云广特高压直流输电系统和贵广二回高压直流输电系统共用接地极模式是可行的。     

小电流接地电网单相接地故障的小波选线方法

中性点非有效接地配电网发生单相接地故障时,尽快选出故障线路对电网运行有重要意义,但选线问题迄今尚未能很好解决。在分析了小电流接地电网发生单相接地时暂态特征的基础上,提出应用小波变换提取故障暂态信息,实现故障选线的方法。由于利用暂态量,该方法适应性、灵敏性均优于现有的基于稳态量方法。     

The effects of very-high-resistance grounding on the selectivity ofground-fault relaying in high-voltage longwall power systems

With the advent of high-voltage (greater than 1 kV) utilization circuits on longwall mining equipment in the late 1980s, the Mine Safety and Health Administration (MSHA) initially required maximum ground-fault current limits of 3.75 A for 4160 V systems and 6.5 A for 2400 V systems. (It should be noted that the Code of Federal Regulations defines low voltage, medium voltage, and high voltage for mine power systems as 0-660 V, 661-1000 V, and greater than 1000 V, respectively.) Ground-fault relay pickup settings were not permitted to exceed 40% of the maximum ground-fault current. Shortly thereafter, the MSHA began, and presently continues, requiring a much lower maximum ground-fault current limit of 1.0 A, or even 0.5 A, with ground-trip settings of 100 mA. Shielded cables, which have significantly more capacitance than their unshielded counterparts, are required for high-voltage applications in the mining industry. In an earlier paper, the author showed that with the long cable runs of a high-voltage longwall system, capacitive charging currents could easily exceed grounding-resistor currents under ground-fault conditions. As a result, overvoltages from inductive-capacitive resonance effects can occur. Because of the large system capacitance and low ground-trip setting, the relay selectivity of the ground-fault protection system may also be compromised. Therefore, an analysis of a typical 4160-V longwall power system that utilizes very-high-resistance grounding (ground-resistor-current limit of 0.5 A) is performed to determine if potential problems exist with the selectivity of ground-fault relaying     

Alarm processing in electrical power systems through a neuro-fuzzy approach

This work presents a methodology that combines the use of artificial neural networks and fuzzy logic for alarm processing and identification of faulted components in electrical power systems. Fuzzy relations are established and form a database employed to train artificial neural networks. The artificial neural networks inputs are alarm patterns, while each output neuron is responsible for estimating the degree of membership of a specific system component into the class of faulted components. The proposed method allows good interpretation of the results, even in the presence of difficult corrupted alarm patterns. Tests are performed with a test system and with part of a real Brazilian system.     

High-speed measuring converter of frequency for automatics of electrical power systems

A settlement expression for a high-speed measuring converter of frequency has been proposed. The results of computer simulations and experimental research were given