Fault impedance estimation algorithm for digital distance relaying

Fault impedance is one of the major parameters that must be estimated accurately in digital distance relaying application. In this paper, a new algorithm is proposed based on symmetrical components theory. The proposed algorithm has computational advantage over previously suggested symmetrical components based algorithms. A procedure for applying shunt fault conditions to the sequence equations to estimate fault impedance of the protected transmission line is discussed. The Alternative Transient Program (ATP) that is available on personal computers was used in evaluating the proposed algorithm. ATP models a power system and simulates many fault conditions on a selected transmission line. Fault data obtained were used in calculating fault impedance using the proposed algorithm. Fault impedance estimates were inserted in relay characteristics to determine suitability of the proposed algorithm for first zone distance protection. Sample results of these studies which show stable fault distance estimates are presented and discussed in the paper     

基于MRAS的异步电机转子时间常数实时辨识

介绍了一种基于模型参考自适应(MRAS)的感应电机转子时间常数实时辨识方法。根据MRAS系统中参考模型和可调模型的状态误差调节可调模型的参数,在线辨识转子时间常数。理论分析证明该算法具有李雅普诺意义下的全局稳定性。最后对该算法进行了仿真验证。     

基于最短电气距离的运行方式组合方法

根据复杂网络理论,将大型电力系统用带权网络模型来描述,基于此模型下的节点最短电气距离提出了一种运行方式组合方法.该方法利用节点最短电气距离表征节点间电气联系强弱的特点,给出了故障电流计算和分支系数计算的最短电气距离判据,据此找到系统内对故障电流和分支系数影响大于某一阈值的厂站,将其纳入进行方式组合,以达到优化运行方式组合的目的.     

An adaptive distance relay based on transient error estimation of CVT

Simple delay solutions are usually used to prevent transient overreach caused by the transient error of a capacitor voltage transformer (CVT), which is very harmful to the safety and stability of operation of the power system. A proposed real-time CVT transient error estimation approach based on the chosen fundamental wave algorithm and the rated CVT parameters consists of two stages. The first stage obtains the error coefficient. The second stage estimates the measured error of the voltage amplitude according to the secondary side voltage. A novel adaptive distance relay approach is proposed, which can adjust operating thresholds according to the error. The approach hardly affects the performance for lines of normal length and operates rapidly for short lines with close-in faults, which is verified by the simulation studies. The overall performance is improved greatly in comparison with the general approach for distance relays.     

Real-time estimation of the electric parameters of an inductionmachine using sinusoidal PWM voltage waveforms

This paper studies the parameter estimation of induction machines. The problems associated with the parameter estimation of induction machines are analyzed through sensitivity functions. Then, models and a procedure to estimate a set of four basic parameters (r_s, σl_s, l_s, and τ_r) are proposed. The discrete-time parameter estimation models are written in the δ operator specifically because it provides good numerical properties at high sampling rates, where the discrete-time model approaches its continuous-time equivalent. This feature permits the direct estimation of the continuous-time parameters. The main feature of the proposed procedure is the possibility to estimate the parameters by using sinusoidal signals, and without the measurement of the machine speed. The experimental results obtained with the proposed estimation procedure are presented and demonstrate that it is possible to map the parameters in terms of the operating conditions of the induction machine     

Time domain solution of fault distance estimation and arcing faultsdetection on overhead lines

In this paper a new numerical algorithm for arcing faults detection and fault distance estimation is presented. The solution is given in the time domain. It is based on the line terminal voltages and currents processing. A simple new mathematical model of arc voltage is introduced in the estimation. Thereby, the more accurate approach to fault location is derived, particularly for the close-in faults. The new algorithm can be utilized for blocking the automatic reclosing. The unknown model parameters, including the line resistance and inductance, fault resistance and arc voltage amplitude, are estimated by using the least error squares method. The new algorithm is successfully tested through computer simulation and laboratory tests     

Strengths and limitations of a new phasor estimation technique to reduce CCVT impact in distance protection

This paper evaluates the performance of a new least squares approach that improves the accuracy and speed of convergence of the voltage phasors estimated during CCVT transient conditions. A justification of the validity of the linear mathematical model for the CCVT used is provided together with a short study about the risk of transient ferroresonance. Also, a discussion is presented about operating times of numerical distance relays and the importance of the new phasor estimation considered. The methodology followed to achieve a realistic evaluation in a variety of scenarios is presented. The results show the improvements achievable in most conditions, but also highlight an example scenario where the new method has limitations.     

5 GHz goes the distance for home networkng

Today, there are a number of basic networking technologies that can support data-centric home networking, including 802.11b, HomeRF, and Bluetooth. As with most new markets and technologies, what users want their home network to do is rapidly changing and evolving. Today's early-adopters want more from their home networks than just sharing PC peripherals; they want to be able to send their digital entertainment content (digital pictures, MP3 audio, and DV-based video) throughout their homes. As this "early-adopter market" rapidly changes into a mass market, today's home network must evolve to where it supports not only TCP/IP-based data, but also audio and video data that require QoS. This evolution will require changes in the architecture and implementation of wireless networks. Air5 is a solution for handling the demands of wireless home networking. Based on the lEEE802.11a PHY-layer specification, it includes enhancements for delivering range and throughput levels. Air5 also delivers triple-DES security and guaranteed QoS performance through its TDMA-based synchronous MAC. There are over 40 companies developing 5-GHz based networking technologies today, so this will be a highly competitive technology evolution.     

PROFINET实时通信技术剖析

PROFINET是一种新的实时以太网标准,本文介绍了PROFINET的技术优势并且详细分析了PROFINET的实时通信技术尤其是等时同步实时通信技术。     

隧道照明光源的光色及可见度研究

该文阐述了隧道照明光源的光色与小目标可见度之间的关系。在两条实际隧道中对三种光源照明下的小目标可见度进行了实际的测量和计算,并且提出了小目标显色性的视觉实验方法。为研究隧道照明的小目标可见度打开了新的思路。     

嵌入式计算机在车载雷达移动式冷源控制中的应用

介绍了嵌入式计算机PC/104在移动式冷源控制中的应用,分析了8259可编程中断控制编程方法以及虚拟仪表技术的算法.     

锅炉效率实时计算的困难及解决方法

针对常规锅炉效率计算方法在现场分析计算中存在的困难,在分析综合大量文献资料的基础上,提出了相应的解决方法,建立了相应的简化计算模型。新方法只需测定燃煤的工业分析成分、采集排烟温度、氧量和参考温度等运行参数,就能解决上述问题,新方法简化了测量与计算,因此特别适用于热电厂锅炉的日常运行监控。     

混联水电站群实时联合优化调度

本文研究一种混联水电站水库群中长期优化调度的多维动态规划模型的求解方法。在编程中充分利用向对象的C＋＋语言的优势,并采用DDDP法减少状态可行域,使得以往被认为具有“维数灾”的多维问题能直接求解。     

基于多单片机的模型直升机机载测控系统设计

遥控模型直升机在军事侦察领域具有广泛用途,其控制系统要求可靠性高、便携性好。多单片机协调综合使用A/D采集、串行口数据读写、PWM信号读取与产生、中断与定时编程等一系列技术,完成多传感器数据采集与执行器控制任务,实现模型直升机机载测控功能。克服嵌入式系统开发中存在的体积重量缺陷,具有较好的便携性和机动性。在平台试验中,系统能够根据测量数据做出正确的控制决策,功能满足遥控模型直升机测控系统要求。     

Wavelets for contrast enhancement of digital mammography

Multiresolution representations provided an adaptive mechanism for the local emphasis of features of importance to mammography. In general, improvements in image contrast for multiscale image processing algorithms were superior to those obtained using existing competitive algorithms. These initial results are encouraging and suggest that wavelet based image processing algorithms could play an important role in improving the imaging performance of digital mammography. In part 2, features blended into the mammograms were "idealized" representations of the types of objects that are of primary interest to mammographers. The resultant mammographic images were appropriate for the purpose of demonstrating improved image contrast made possible by wavelet based image processing algorithms. These images were also useful for comparing multiscale wavelet based algorithms with existing image processing algorithms. The test results obtained in this study, however, cannot be directly extrapolated to clinical mammography. In addition, it is also important to study possible image artifacts introduced by new wavelet filters, which may increase the false positive rate     

一种电力系统失步解列面的实时搜索方法

为故障后失去稳定的电力系统确定解列断面以平息系统振荡可以防止系统完全崩溃,如何快速寻找不同失稳模式下的解列面成为解列控制的关键问题之一。提出电力系统失步解列面实时搜索方法,该方法的优化目标为解列后各孤岛内发电机和负荷不平衡尽可能小。方法包含3个阶段:基于潮流追踪的系统分区、基于发电机分群信息的解列面初步确定和基于初步解列断面的解列断面改善。算法具有时间复杂度小、计算速度快的特点。基于C++语言编制实时搜索程序,对IEEE118节点系统进行解列面搜索仿真计算,仿真算例验证了方法的有效性和快速性。     

Electromechanical distance measure for decomposition of power systems

A concept of electromechanical distance measure which reflects the interaction among the machines during a transient is presented. This measure is then used as a criterion for decomposing the power system into regions, each requiring different levels of model complexity. The complexity of models for regions decreases progressively away from the point of fault. Grouping of coherent generators within each region can also be done using the results of this analysis. The analysis takes into account the fault location, magnitude of disturbance, and changes in boundary between the study area and the external system.     

数字实时仿真在控制和保护系统测试中的应用

HVDC和FACTS装置的控制和保护系统在投运前必须进行仿真测试,以验证系统性能.文中结合实际工程项目,详细阐述了数字实时仿真系统进行HVDC和FACTS装置控制和保护系统实时测试的原理和过程.在此基础上进一步阐述了数模混合实时仿真系统的结构和应用情况,同时提出了先进集成混合实时仿真系统的架构和原理.混合实时仿真系统可经济有效地扩大实时测试系统的规模.项目中装置投运后现场试验的结果验证了实时测试的准确性.