NEW PRINCIPLE FOR DIRECTIONAL COMPARISON CARRIER PROTECTION OF EHV TRANSMISSION LINES

The increasing scale and complexity of power systems require high performance and high reliability of power system protection.Protective relaying based on directional comparison with power line carrier or microwave channels is the most suitable protection scheme for long distance EHV transmission lines and is widely used in power systems.The key element of such protection is a directional relay used to discriminate the fault direction.In order to overcome the disadvantages of conventional directional relays,the authors of this paper put forward the directional comparison carrier protection based on the artificial neural network(ANN).The protection is extensively tested using electromagnetic transient program (EMTP) under various electric power system operating and fault conditions.It is proved that the directional comparison carrier protection based on ANN,which can recognize various fault patterns of the protected transmission line(such as fault direction,fault phases etc.)correctly in any kind of operating and fault conditions and the whole process,is satisfactory for EHV transmission line protection.

Research on the longitudinal protection of a through-type cophase traction direct power supply system based on the empirical wavelet transform

This paper proposes a longitudinal protection scheme utilizing empirical wavelet transform(EWT)for a through-type cophase traction direct power supply system,where both sides of a traction network line exhibit a distinctive boundary structure.This approach capitalizes on the boundary’s capacity to attenuate the high-frequency component of fault signals,resulting in a variation in the high-frequency transient energy ratio when faults occur inside or outside the line.During internal line faults,the high-frequency transient energy at the checkpoints located at both ends surpasses that of its neighboring lines.Conversely,for faults external to the line,the energy is lower compared to adjacent lines.EWT is employed to decompose the collected fault current signals,allowing access to the high-frequency transient energy.The longitudinal protection for the traction network line is established based on disparities between both ends of the traction network line and the high-frequency transient energy on either side of the boundary.Moreover,simulation verification through experimental results demonstrates the effectiveness of the proposed protection scheme across various initial fault angles,distances to faults,and fault transition resistances.

Designing a Protection Scheme in Micro-Grid Systems with DG Using Central Protection Unite and Multiple Setting Group Protection Relays

Distributed generators now is widely used in electrical power networks, in some cases it works seasonally, and some types works at special weather conditions like photo voltaic systems and wind energy, and due to this continuous changes in generation condition, the fault current level in network will be affected, this changes in fault current level will affect in the coordination between protection relays and to keep the coordination at right way, an adaptive protection system is required that can adaptive its setting according to generation changes, the fault current level in each case is evaluated using ETAP software, and the required relay setting in each case is also evaluated using Grey Wolf Optimizer (GWO) algorithm, and to select suitable setting which required in each condition, to select the active setting group of protection relay according to generation capacity, central protection unite can be used, and to improve protection stability and minimizing relays tripping time, a proposed method for selecting suitable backup relay is used, which leads to decrease relays tripping time and increase system stability, output settings for relays in all cases achieved our constrains.

Analysis of a Verifying Method of Consistency Between CT/ PT Polar-ity and Directional Protective Relaying

The coordination correctness of Nuclear power plant current transformer (CT)/ voltage transformer (PT) polarity and relay protection is often verified through the dynamic test on the unit no load / load operating conditions. This paper proposes a test method to prevent and circumvent the failure of the dynamic test abnormality caused by the static power test before the plant power is applied and the whole group is started. Reduce the dynamic test workload and test difficulty, to ensure that the dynamic test safety risk control and control in the state.

Interactions between γ-TiAl melt and Y_2O_3 ceramic material during directional solidification process

A γ-TiAl alloy with nominal composition of Ti-47%Al（molar fraction） was directionally solidified in an alumina mould with an Y2O3 protective coating.The effects of processing parameters（melting temperature and interaction time） on the metal-coating interface,microstructure and chemical composition of the alloy were evaluated.The result shows that the Y2O3 protective coating exhibits an effective barrier capability to avoid direct contact between the mould base material and the TiAl melt,although the Y2O3 coating is found to suffer some erosion and be slightly dissolved by the molten TiAl due to the coating-metal interactions.The directionally solidified alloys were contaminated with Y and O,and Y2O3 inclusions were dispersed in the metal matrix.The reason for this metal contamination is the Y2O3 coating dissolution by the TiAl melt.One mode of the interaction between Y2O3 and the TiAl melt is dissolution of yttrium and atomic oxygen in the melt by reaction Y2O3（s）=2Y（in TiAl melt）＋3O（in TiAl melt）.Both the extent of alloy contamination and the volume fractions of Y2O3 inclusions depend on the melting temperature and the interaction time.

Consolidated Lightning Protection Methods of Landfill and Incineration Plants and Its Application Technology Investigation

Taking lightning-protection engineering of Wuhan Changshankou landfill and incineration plants for the example,in this article,we have discussed the integrated technology of direct lightning protection by early streamer emission lightning rod,lifting lightning rod and mobile lightning rod. Additionally,lightning protection methods and measures of landfill with large receiving area of lightning strike and landfill gas and incineration plant with irregular landfill cell are explored.

A Study on the Transmission Line Transient Protection Containing Static Synchronous Compensator

This paper focuses on the transient protection of transmission line with FACTS Devices;the principle and mathematical model of static synchronous compensator (STATCOM) has been analyzed. And feasible control strategy has been proposed considering the voltage source inverter (VSI) as a core part of the FACTS components. The simulation results verify the rightness using electromagnetic transient simulation software PSCAD/EMTDC to set up electromagnetic transient model.

Design and operation of 500kV transmission line protection in China

The protective devices we developed for 500 kV transmission lineshave been implemented in UHV power systems in China for manyyears.The quality of the product and the principle of the system have stoodsevere tests in practical operation.In this paper,the general characteristics of 500 kV lines in China aresystematically analysed.The requirements of protection on 500kV linesare specifically discussed,Two design schemes for 500kV protection areproposed,and the results of practical test and operation are given.Theyverified that the schemes proposed overcome the difficulties found inimported relay systems.

Optimal coordination of directional over current relays using evolutionary programming

Co-ordination of directional over current relays(DOCR) requires the selection and setting of relays so as to sequentially isolate only that portion of the power system where an abnormality has occurred.The problem of coordinating protective relays in electrical power systems consists of selecting suitable settings such that their fundamental protective function is met,given operational requirements of sensitivity,selectivity,reliability and speed.Directional over current relays are best suited for protection of an interconnected sub-station transmission system.One of the major problems associated with this type of protection is the difficulty in coordinating relays.To insure proper coordination,all the main/back up relay pairs must be determined.This paper presents an effective algorithm to determine the minimum number of break points and main/back up relay pairs using relative sequence matrix(RSM).A novel optimization technique based on evolutionary programming was developed using these main/back up relay pairs for directional over current relay coordination in multi-loop networks.Since the problem has multi-optimum points,conventional mathematics based optimization techniques may sometimes fail.Hence evolutionary programming(EP) was used,as it is a stochastic multi-point search optimization algorithm capable of escaping from the local optimum problem,giving a better chance of reaching a global optimum.The method developed was tested on an existing 6 bus,7 line system and better results were obtained than with conventional methods.

Protective benefit of folded linear HDPE board sand fences along the Golmud-Korla Railway,China:Field observation and wind tunnel study

The Milan Gobi area of the Golmud-Korla Railway in northwest China is located in the lower dispersal area of the mountain pass and has strong winds with evident double wind direction characteristics.This study introduced a novel sand fence deployment technique,termed‘folded linear deployment',designed to position the sand fence orthogonally to the two predominant wind directions for optimal protection.This study used wind tunnel and field tests to evaluate the wind and sand flow characteristics,as well as the windproof and sandresistant performance of folded linear HDPE(Highdensity polyethylene)board sand fences.The results suggest that the airflow around the fence creates clear zoning characteristics.The deceleration area on the BSF(backwind side of the sand fence)is much larger than that on the DSF(downwind side of the sand fence).Thus,sand particles are primarily deposited on the BSF.At different wind speeds,the airflow at 2 and 5 h on the DSF is not disturbed.The WSP(wind speed profile)presents a logarithmic distribution.The airflow is disturbed at 1-20 h on the BSF,and the WSP gradually deviates from the logarithmic law.However,as the airflow moves away from the fence,the WSP gradually approaches a logarithmic distribution.Meanwhile,the WPE(windproof efficiency)and SRE(sand-resistant efficiency)of the sand fence exceed 80%.In addition,the results of wind tunnel tests are compared with those of field tests.The overall dispersion is good,and the best dispersion is found at z/H=2.00,indicating good agreement between the two test results.This study provides a scientific basis for the design of sand hazard control measures,similar to the railway project in the Gobi Gale area.

Special Problems in Pilot Protections of Transmission Lines Connecting Wind Farms

As the penetration of wind power into power grids increases,higher demands are made on the stability and protection of power systems.Unlike traditional synchronous generators,wind turbines are different on the short-circuit and impedance characteristics,thus some problems exist in pilot protections of transmission lines connecting wind farms.When a single-phase fault occurs on a transmission line,the phase selector based on current-difference sudden-change may mistake the single-phase fault for a phase-to-phase fault.This paper studies the impedance characteristics of an asynchronous wind generator,and analyzes the behavior of a fault phase selector under different conditions.Then,the paper explains that inequality between positive and negative branch coefficients is the cause for the mal-operation of the fault phase selector.Finally,some simulations are done in MATLAB to validate analysis results.

论“慎捕”的法规范控制体系及实践问题破解

历次修法中涉及逮捕的制度机制的演进轨迹和条文变化的内在逻辑表明,为实现“慎捕”目标,《中华人民共和国刑事诉讼法》(以下简称《刑事诉讼法》)已初步构筑起一套结构严谨、衔接有序、层次分明的关于逮捕权的法规范控制体系。该体系在事前的权力配置阶段“两次分离”逮捕权,以具体社会危险性评估为重心改造逮捕要件;在事中的权力行使阶段以“兼听则明”为原则设计了充分听取控辩双方意见的审查逮捕机制;在事后的权力制约阶段要求检察院、法院及时纠正撤销错捕决定,释放犯罪嫌疑人。从司法办案的角度来看,现有的法规范控制体系在规则制定和程序执行时仍有不足和缺漏,如逮捕权分离不彻底,控辩意见“兼听”机制保障不充分,径行逮捕条件设计机械、不周延,当事人对错捕的救济途径缺失等。本轮《刑事诉讼法》修改应坚持“实践—规范”的互动逻辑,关注司法实践,将解决和弥补逮捕中的权力运行失范和权利保障不足等现实问题作为修法方向,破难题、开新局,不断推动中国刑事诉讼法治现代化进程。

Novel directional comparison protection for distribution lines

For quickly clearing up a fault of distribution lines, which concerned with complex structure and operating modes, a directional comparison protection is necessary. The paper evaluated the traditional directional relay through modeling a typical distribution system and presented a novel negative sequence directional relay and a new directional comparison protection scheme specially designed for distribution systems. In the relay and the protection scheme, a particular negative sequence component has been constructed to solve the problem that there is no negative sequence component in a symmetrical fault case so that they could operate correctly in both asymmetrical fault and symmetrical fault. Extensive EMTP simulation studies proved that the protection schemes are able to provide fast and reliable responses for all fault conditions. In particular, they are able to give correct responses adapting to the change of system operation conditions, including the changing of system configuration, power flow direction, and source and tapped-offload conditions.

Novel transient-energy-based directional pilot protection method for HVDC line

This paper proposes a novel directional pilot protection method based on the transient energy for bipolar HVDC line.Supposing the positive direction of current is from DC bus to the DC line,in the case of an internal line fault,the transient energies detected on both sides of the line are all negative within a short time,which denotes the positive direction fault;while for an external fault,the transient energy on one end is positive,which means a negative direction fault,but the transient energy on the opposite end is negative,which indicates that the fault direction is positive.According to these characteristics,an integration criterion identifying fault direction is constructed.In addition,through setting a fixed energy threshold,the faulted line and lightning disturbance can also be discriminated.Simulation results from UHVDC transmission system show the validity of the proposed protection method.

Summary of Useful Concepts About the Coordination of Directional Overcurrent Protections

This paper summarizes some useful concepts about the coordination of directional overcurrent protections.The following key topics are described:the analysis of systems in a ring configuration and only one source of short-circuit currents;the impossibility of obtaining selectivity for all the possible system configurations with multiple sources;the need for inverse functions in order to obtain selectivity in systems with multiple sources;the coordination with protections for radial loads;the coordination between instantaneous and delayed functions;the considerations to select the pickup values;the influence of contributions from motors to short circuit currents;the transient configurations due to sequential trips at both line ends;the influence of dynamic behavior of overcurrent functions;the influence of stability constraints;other specific considerations for ground functions;some specific considerations for systems with distributed generation.A summary of these points and their effect on the coordination of directional overcurrent protections is not available in the current literature.This novel description should facilitate the inclusion of these key points in research and coordination studies related to these protective functions.

Limitations of Lightning Rods in Preventing Direct Lightning Strikes

Since ancient times,lightning disasters have undoubtedly been an unstoppable threat to humanity.During thunderstorms,lightning often damages objects on the ground,such as buildings and structures.Since Franklin invented the lightning rod in 1752,lightning rods have been used worldwide to prevent direct lightning strikes in various fields such as high-voltage power transmission lines,outdoor chemical sites,highways,land and sea wind farms,and forest lightning fire protection.It has been proven that lightning accidents still occur frequently in places where lightning rods are installed and the protective angle method is used.In order to further study the protective effect of lightning rods and identify the shortcomings of lightning rod protection,negative lightning strikes are taken as the research object,to analyze the limitations of lightning rods in preventing direct lightning strikes from the working principle of lightning rods.

一种适用于混合双极直流输电的纵联方向保护方法

直流输电线路通常是以大电感和直流滤波器作为边界,故障行波在边界发生折射和反射时,其行波能量也会因为电感和滤波器的存在而被吸收,导致区内、外高频行波能量产生差异.当故障发生为正方向故障时,其高频前行波能量小于高频反行波能量;当故障发生为反方向故障时,其高频前行波能量大于高频反行波能量.由此特征提出了一种基于前、反行波高频能量差异的纵联方向保护,该保护采用小波包变换提取行波的高频能量,利用前行波与反行波在区内故障和区外故障时的高频能量差异判别故障.仿真结果表明,该保护能快速准确地识别故障,并且不受故障类型、过渡电阻以及故障发生位置距离和噪声的影响,具有一定的实用性.

级联多端特高压直流控制保护系统配置及策略

该文针对金上直流工程主回路拓扑结构与运行方式的特点,设计了送端分址级联多端特高压直流控制保护系统的配置方案;提出送端分站的高、低压换流器的电压平衡控制方案,根据送端两站间通信条件,切换采用附加电压平衡控制的触发角协调控制和串联两换流器一个定电压、另一个定电流的控制策略;基于送端分站级联拓扑,研究了其直流保护功能配置方案,并提出针对送端站1内的极区/换流器区故障或者送端两站之间直流线路永久故障的快速清除方法。基于控制保护工程样机的RTDS闭环仿真结果表明,该级联多端特高压直流控制保护系统可以满足实际工程应用的要求。

基于扩展边界的柔性直流输电网区域纵联保护

直流保护是保证多端柔性直流输电网安全的关键。行波保护动作速度快,可满足现有柔直电网对保护速动性的要求,但存在采样频率较高、可靠性不足、在线路边界受限时灵敏性较低的问题。针对上述问题,充分利用换流站及其各出线上的平波电抗器组成扩展边界,提出新型区域纵联方向保护原理。首先,分析扩展边界两侧电压的故障特征,利用扩展边界对电压时域波形的显著衰减形成的正反方向不同的故障特征来构造方向元件,构成纵联方向保护。该保护原理同时具备母线故障判别能力,并与相邻保护协调配合形成区域保护方案。其次,分析行波多次折反射过程对方向元件的影响,并给出保护动作时间。最后,进行仿真分析和对比验证。所提保护原理对采样频率要求低,在高阻故障、强噪声以及边界特性削弱时仍具有较高的灵敏性和可靠性。