低压电力系统无功补偿实用电路(3)

5 机械旋转类无功补偿装置机械旋转类无功补偿设备包括同步调相机、同步发电机和同步电动机,它们均能通过励磁来调节无功功率。由于它们都含有机械旋转部分,所以属于旋转型无功补偿设备。旋转型无功补偿设备的缺点是体积大、维护成本高、噪声大,动态响应时间较长、出现故障后难于在短时间内得以恢复等[1]。同步调相机可以看成是一种不带任何负载的同步电动机。它可通过励磁调节控制同步电动机的无功电流,进而改善受端功率因数,起到无功补偿的作用。

浅谈电力系统电气二次回路常见故障及防范措施

随着时代的快速发展,电气技术的发展是日新月异,已全面进入智能化水电、电网的发展阶段,在这个飞速发展的时代,保证电力系统安全的可靠运行和提高电能质量具有及其重要的意义。在电力系统中的二次回路就好比是我们人体筋脉,那里不畅通,那里就失去功能,在电气二次设备事故中,因二次回路的故障引发的事故所占比例相对较大。本文通过水电站和变电站的电气二次设备安装、检修和调试过程中二次回路接线虚接、端子松动、寄生回路、二次电缆绝缘损坏、接点不通发卡等实例,以及继电保护装置、自动装置的二次原理,具体分析电力系统中二次回路发生故障的原因和防范措施,论证电力系统二次回路的重要性。

电力系统二次回路及继电保护调试探析

二次回路是继电保护系统的重要组成部分,就整个继电保护系统而言,二次回路虽只是一个较小的方面,但它的故障不仅直接影响继电保护设备动作的正确性,而且关系到系统的安全稳定运行.因此,电力系统二次回路的试验工作作为继电保护设备投用过程中的一个重要环节,必须得到足够重视.

电力系统继电保护二次回路检修问题及对策探析

现如今,人们的生活质量得到了很大程度的提升,同时对电力的需求也有了很大程度的增加,在电力行业带来发展契机的同时,也增加了其发展的压力。为了进一步满足人们的生活需求,相应的电力企业只有注重电力系统继电保护二次回路检修,才可以确保电力系统的稳定性运行,这可以为人们营造一个相对安全稳定的生活环境。维护社会的稳定性。基于此,本文在阐述电力系统继电保护二次回路检修概念的同时,对检修过程中存在的问题也进行了分析,并总结了相应的对策,以期可以为电力行业的后续发展提供一定的借鉴。

基于JavaScript的电力系统二次回路动态演示培训系统

介绍了一种采用JavaScript脚本语言编写，基于RPG Maker MV游戏制作引擎的电力系统二次回路动态演示培训系统。

电力系统二次回路及继电保护调试探析

近年来社会用电需求的不断增大,电力工程建设数量也逐渐增多。继电保护在电力系统运行中发挥着重要作用,为系统整体运 行的安全性与稳定性提供了必要的保障。二次回路是继电保护系统的重要组成部分,就整个继电保护系统而言,二次回路虽只是一个较小 的方面,但它的故障不仅直接影响继电保护设备动作的正确性,而且关系到系统的安全稳定运行。因此,电力系统二次回路的试验工作作 为继电保护设备投用过程中的一个重要环节,必须得到足够重视。本文就电力系统二次回路及继电保护调试展开探讨。

Petri网描述的继电保护动作逻辑时序建模

Petri网理论具有完善的理论证明依据,是离散动态系统建模的有效工具。该文基于Petri网理论,介绍了一种新的继电保护建模思路。保护装置可以看成一个离散动态系统。利用Petri网中并行、冲突、资源分享等特性,对继电保护中的动作逻辑演化及二次回路动态进行描述,建立了保护装置的PN模型。最后就RCS-901A/B超高压线路成套保护装置进行了工作原理分析和性能评估,证明了所提方法的有效性。

Research on large-scale cascading failure of power systems using synergistic effect

This paper discusses the primary causes from the point of synergistic effects to improve power system vulnerability in the power system planning and safety operation. Based on the vulnerability conception in the complex network theory the vulnerability of the power system can be evaluated by the minimum load loss rate when considering power supply ability.Consequently according to the synergistic effect theory the critical line of the power system is defined by its influence on failure set vulnerability in N-k contingencies.The cascading failure modes are proposed based on the criterion whether the acceptable load curtailment level is below a preset value.Significant conclusions are revealed by results of IEEE 39 case analysis weak points of power networks and heavy load condition are the main causes of large-scale cascading failures damaging synergistic effects can result in partial failure developed into large-scale cascading failures vulnerable lines of power systems can directly lead the partial failure to deteriorate into a large blackout while less vulnerable lines can cause a large-scale cascading failure.

Modeling of electrode system for three-phase electric arc furnace

To simulate the process of electrode operation, a dynamic model describing the electrode system of three-phase electric arc furnace was developed. This new model can be divided into three submodels in terms of the practical situation. They are the power supply system model the electric arc model and the hydraulic actuator system model. According to the basic circuit theory, the power supply system model where the high voltage transmission circuit and mutual inductances were considered, was set up. The electric arc model, which was novel for the electrode control, served as the electrical load and was connected to the power supply system model. The hydraulic actuator system model consists of the proportional valve part that is modeled to capture the dead-zone nonlinear characteristics and the hydraulic cylinder part where the impact of the load force is taken into account. By comparing simulation data and actual data, the results show that the electrode system model is proved to be accurate.

Power swing and voltage collapse identification schemes for correct distance relay operation in power system

The new techniques were presented for preventing undesirable distance relay maloperation during voltage collapse and power swings in transmission grids. Initially, the work focused on the development of a fast detection of voltage collapse and a three-phase fault at transmission lines by using under impedance fault detector (UIFD) and support vector machine (SVM). Likewise, an intelligent approach was developed to discriminate a fault, stable swing and unstable swing, for correct distance relay operation by using the S-transform and the probabilistic neural network (PNN). To illustrate the effectiveness of the proposed techniques, simulations were carried out on the IEEE 39-bus test system using the PSS/E and MATLAB software.

Research on Multi Level Dynamic Voltage Compensator based on MMC

The modular multilevel converter （MMC） is a highly modular, easy to expand; the output voltage waveform is good, especially suitable for application in high voltage power system. This article first introduces the circuit topology and principle of MMC, and the main technical characteristics of MMC. And according to the relationship between the drop power voltage and the load power factor, proposed three working modes of the minimum energy compensation strategy. It is shown that MMC has good application prospect in future medium or high- voltage high power applications, especially be one of candidates for HVDC system application.

Modeling and Controlling of an Active Power Filter Using Photovoltaic System with Reduced Energy Storage Capacitor

A novel three-phase active power filter （APF） circuit with photovoltaic （PV） system to improve the quality of service and to reduce the capacity of energy storage capacitor is presented. The energy balance concept and sampling technique were used to simplify the calculation algorithm for the required utility source current and to control the voltage of the energy storage capacitor. The feasibility was verified by using the Pspice simulations and experiments. When the APF mode was used during non-operational period, not only the utilization rate, power factor and power quality could be improved, but also the capacity of energy storage capacitor could sparing. As the results, the advantages of the APF circuit are simplicity of control circuits, low cost, and good transient response.

Dynamics and circuit implementation of three simplified chaotic systems

To improve the performance of chaotic secure communication,three simplified chaotic systems with one variable parameter were investigated.Basic properties were analyzed including symmetry,dissipation and topological structure.Complex dynamical behaviors of the systems including chaos and periodic orbits were verified by numerical simulations,Lyapunov exponents and bifurcation diagrams.Interestingly,the three systems were integrated in a common circuit,and their dynamical behaviors were easily observed by adjusting regulable resistors R28,R14 and R17,respectively,and the relations between the variable resistor and the system parameter were deduced.The circuit experiment results agree well with the simulation results.Finally,a secure communication scheme based on chaos shift keying(CSK) was presented,which lays an experiment foundation for chaotic digital secure communication.

Electro Energetic Technological Control in Eastern Siberia Railway

By system analysis and imitating modeling authors show the most effective modern techniques for railway electric systems control. Modem measure technologies PMU-WAMS and smart grid allow to solve real time tasks of centralizing control of railway electric systems. Quantity characteristics of control effectiveness are determined. According to computer modeling the situation approach is available for practical tasks of railway electric system control.

Power System Modelling and Fault Analysis of NamPower＇s 330 kV HVAC Transmission Line

Electric power systems usually cover large geographical areas and transmission facilities are continuously increasing. These power systems are exposed to different environmental conditions which may cause faults to occur on the system. Different types of studies are usually done on electric power systems to determine how the system behaves before, during and after a fault condition. The behaviour of variables of interest such as currents, voltage, rotor angle and active and reactive power under fault conditions are studied and observed to help determine possible causes of faults in a power system. The objective of this paper is to investigate a fault that occurred on the 330 kV transmission line between Ruacana power station and Omburu sub-station, the fault caused all the generators at Ruacana power station to trip and consequently caused a blackout at the power station that lasted for 6 h. Preliminary findings showed that the observed fault was an earth fault but the exact type of earth fault was however not known at the time. This research investigation sets out to determine the exact fault that occurred; the most probable cause of the fault, and propose possible solutions to prevent reoccurrence of such a fault. The section of the power network in which the fault occurred was modelled using DigSilent Power Factory software tool, and transient fault analysis was carried out on the model for different fault conditions. Results obtained were then compared with data obtained from NamPower records to ascertain the type of fault.

Investigation of Shunt Active Power Filters in Railway Systems, Substation Installation

This paper investigates the performance of SAPFs （shunt active power filters） which are introduced in order to address the quality issues in electrified railway supply systems. These filters can be installed at either the S/S （substation） end or at the SP （sectioning post） of the railway feeding power system. In this investigation novel control algorithms, based on the synchronously rotating frame of reference, are proposed for the case when the SAPF is installed at the substation end and its performance is assessed. The effectiveness of the proposed control algorithms are illustrated via Matlab/SimPower computer simulations and validated via comparisons with other publications. This investigation demonstrated that when the SAPF is installed at the substation side, it can effectively compensate for the higher harmonic supply current. In addition, the reactive power demand is fully compensated for, leading to close to unity power factor. However, the voltage drop/sag at the locomotive power supply feed point is only partially compensated for.

Long Range Unmanned Aircraft System for Power Line nspection of Brazilian Electrical System

Power line inspection is an essential procedure in the power lines maintenance area, especially thinking about service availability and energy efficiency. Aerial inspection of electric power transmission lines is typically performed using human-piloted helicopters, which is a procedure that is both expensive and prone to accidents taking risks to human beings＇ lives. The work presents a solution based on UAS （unmanned aircraft system） for inspecting power lines. In this context a R ＆ D project of an unmanned aircraft system to be used for performing complete aerial inspection of overhead power lines is being executed by ITA （Instituto Tecnol6gico de Aeron^utica） （Technological Institute of Aeronautics） in Brazil. Special attention is dedicated to the communication system conception in order to comply with Remotely Piloted Aircraft System definition in the context of long endurance operations of the system. It presents a solution based on LTA （lighter than air） platform in order to extend the communication range beyond line of sight.

Prototype Monitoring System for Power Line Inspection by Means of a PandaBoard

The national energy supplier （Eskom in South Africa） supplies electricity through thousands-of-kilometers of overhead power lines. The current methods of inspection of these overhead power lines are infrequent and expensive. In this paper, the authors present the development of a prototype monitoring system for power line inspection in South Africa. The developed prototype monitoring system collects data （information） from the overhead power lines, is remotely accessible and fits into a power line robot. The prototype monitoring system makes use ofa PandaBoard （SBC） with GPS receiver and 5 MP camera to collect data. Hardware fatigue is the biggest problem faced on the overhead power lines and is captured by means of the 5 MP camera and is displayed on a website hosted by the PandaBoard via Wi-Fi. The monitoring system has low power consumption, is light weight, compact and easily collects data. The data obtained from the prototype monitoring system was satisfactory and provides an improved solution for monitoring power lines for Eskom in South Africa.

Fault Current Limiters and Impacts on the System Protection Behavior

A deregulated power market is making short-circuit currents likely to exceed the thermal or mechanical permissible limits of switchgear. Consequently fault current limiters （FCL） become more necessary in power systems. The use of FCLs has an impact on the protection schemes and functions in power systems. Thus, before FCLs can be applied in the network, the impacts on existing protection system must be understood. Depending on the current limiting technique used, today＇s protection concepts may have to be adapted or revised to ensure proper network protection selectivity. A relationship between fault current limiters and protection schemes should be established by taking into account both protection and network specific issues, such as the impact of different FCL technologies, existing and new protection concepts, selectivity and innovative network. This paper is presenting a frame work for accomplishing this task.

Analysis of Short Circuit Faults in a System Fed by Wind Turbine

Short circuit and ground failures that are quite common in power transmission lines are investigated. These failures are designed considering a system that is supplied by this wind system, and analyses are interpreted. In the study, a system is set up and it is fed by the wind turbine. Furthermore, the mathematical model of wind turbine and generator is prepared and the results obtained from the simulation are evaluated. The short circuit and ground fault analyzes were performed separately for each of the three phases. ATP （alternative transient program）-EMTP （electromagnetic transients program） program is used in the analysis and the results obtained were found to be quite compatible.