非全相运行对方向高频保护的影响

对高压线路非全相运行中高频保护的零序功率方向元件和突变量方向元件动作性进行分析,并通过对一起220kV线路保护误动事故实例的分析,指出在非全相运行中方向高频保护应注意的问题。     

基于负荷电流补偿的负序方向保护改进算法

电力系统非全相运行和非全相运行方式下再发生故障的工况,会对负序方向保护的正确动作造成影响。当电压互感器安装于母线侧,非全相运行时,负序方向元件会误动;而非全相运行方式下再发生正向故障时,负序方向元件能正确识别。针对该问题,提出了一种修正的负序方向保护新方案:加入负荷电流补偿来抵消非全相运行时系统中存在的负序电流,使得非全相运行时,负序方向保护能有效不动作,而非全相运行再发生故障时,负序方向保护能有效识别。PSCAD与MATLAB的仿真结果表明,新的保护方案在输电线路非全相运行各种工况下具有很好的实用性。     

发变组非全相及失灵保护电流元件整定计算探讨

以1台600 MW机组的断路器非全相及失灵保护负序和零序过电流元件的整定计算为例,探讨负序和零序过电流元件的整定计算方法,并对各种非全相运行情况下的负序和零序过电流元件的灵敏性进行分析。     

非全相保护原理及应用

针对中宁发电有限责任公司变电所线路及元件非全相保护在设计及运行中存在的问题。结合非全相保护基本原理的分析。提出并制定解决方案。     

发电机组非全相保护的分析与改进

我国发生过多起发电机组非全相运行事故,主要原因是断路器内部的绝缘拉杆被拉断,断路器操作失灵,三相触头中有一相处于闭合位置,此时由于辅助节点不能正确地反映断路器的实际位置,当进行倒闸操作时,断路器虽然处于非全相状态,但是断路器位置不一致判别元件拒动,不能启动非全相保护,所以非全相保护将拒动,导致非全相事故扩大.文中对类似的非全相保护拒动问题进行了分析,并针对非全相保护设计上存在的缺陷提出了改进方法.     

发电机组非全相保护的分析与改进

我国发生过多起发电机组非全相运行事故,主要原因是断路器内部的绝缘拉杆被拉断,断路器操作失灵,三相触头中有一相处于闭合位置,此时由于辅助节点不能正确地反映断路器的实际位置,当进行倒闸操作时,断路器虽然处于非全相状态,但是断路器位置不一致判别元件拒动,不能启动非全相保护,所以非全相保护将拒动,导致非全相事故扩大.文中对类似的非全相保护拒动问题进行了分析,并针对非全相保护设计上存在的缺陷提出了改进方法.     

高压断路器非全相保护的运行技术分析

断路器非全相运行保护的不同技术方案有不同的特点。结合福建省电力系统情况,阐述了配置高压断路器非全相保护的必要性,分析了当前非全相保护的常见方案的技术特点及适用范围,探讨了3／2断路器接线的非全相保护方案的选择,以及设备在运行维护和装设中应注意的事项。     

断路器非全相运行保护在发电厂的应用

断路器非全相运行保护是针对断路器三相位置不一致的保护,原国家电力公司25项反措和国家电网公司18项反措都对断路器非全相保护的配置及实现方法作出了相应规定,各发电厂因为电气主接线和电气主设备等原因,非全相保护的配置和实现方法应有所不同,继电保护人员要正确理解反措,正确、合理地应用非全相保护.     

断路器非全相运行的危害及其预防

文章分析了断路器非全相运行的危害,在断路器非全相运行时,由于电气量不对称会出现负序和零序电流,并产生过电压,使电网的发、供、用电设备受到损害,给电网的安全运行带来了极大的隐患。因此,提出了防止断路器非全相运行的各项预防性措施和在断路器非全相运行时,如何做到正确处理,以避免非全相运行对电力设备的损害。     

反应全相及非全相状态下各种故障的方向元件

本文实现了用相电压补偿方向元件反应三相短路及非全相状态下的两相接地，因而使该方向元件能够反应系统全相及非全相状态下的各种故障，成为高压和超高压输电线路载波保护中性能完善的方向元件。     

COMPLEX POWER IN CIRCUITS WITH MULTIPLE REACTIVE ELEMENTS

ABSTRACT

This paper provides a detailed discussion of how complex powers combine in circuits with multiple reactive or phase dependent elements. Reactive powers in different circuit elements are additive by simple addition if and only if either the currents or the voltages are in phase or 180° out; this condition is met by multiple elements on a given circuit branch, and by multiple circuit branches between common nodes. The phase condition is not met between individual reactive circuit elements on different circuit branches, therefore reactive power cannot be determined using simple addition; a more complex procedure is necessary. The results are of direct importance for properly determining energy storage between multiple circuit elements within an electrical grid.     

Some effects of temperature on multiple column metal oxide devices

Metal oxide elements are capable of dissipating considerable energy in terms of joules per cubic centimeter or joules per gram, and elements of reasonable size are capable of discharging the energy associated with most surge arrester applications. Surge arresters designed using metal oxide elements have been in service since 1976. However, a single column consisting of elements of usual diameter is not capable of discharging a long, 500 kV or 800 kV transmission line under all of the switching conditions generally considered; therefore, metal oxide arresters for application at these voltages are usually designed with two columns of elements in parallel. Furthermore, devices for series capacitors protection or protection of valves and filters in DC converter stations and similar applications are often required to discharge several tens of times more energy than required by station applications, and are hence designed using several columns of elements in parallel. The objective of this paper is to describe some of the effects of temperature on the operation of parallel multiple column devices     

触摸屏手机GUI中分层显示的设计与实现

当触摸屏手机的某个界面同时含有动画和静态文本或图像时,随着动画的刷新,可能会出现静态文本或图像被覆盖的问题。应用分层设计的方法,在某些频繁更新的界面中,把一直不变化的显示元素和频繁变化的显示元素分别提取出来,设置在不同的层中。当界面需要更新时,只需要刷新频繁变化的元素所在的层,而后将两个层合并到真正的屏幕上,解决了动画刷新过程中,可能出现的静态文本或图像被覆盖的问题。详细介绍了层的创建、激活、合并以及释放等操作,实现了动态图像刷新时的精确显示和控件的准确操作,提高了GUI的满意度。     

Load characterization and power conditioner synthesis using higher-order elements

It is shown that virtually all nonlinear and/or time-varying loads that generate harmonic current distortion can be characterized in terms of so-called higher-order circuit elements. The most relevant higher-order elements exploited in this paper are the memristor, meminductor, and memcapacitor. Such elements naturally arise by introducing constitutive relationships in terms of higher-order voltage and current differentials and integrals. Consequently, the power conditioner necessary to compensate for the load current distortions is synthesized similarly. The new characterization and compensation synthesis is applied to the half-wave rectifier and the controlled bridge converter.     

Two‐graph analysis of pathological equivalent networks

Recently, abstract current mirror and voltage mirror elements have been proposed for behavioral modeling of active analog blocks. Such artificial elements and the traditionally used nullor element together are called pathological elements in the literature. Pathological elements are very useful in modeling and analysis of active network. Hence, researchers have been motivated to study symbolic analysis methods for networks containing pathological elements. However, so far, only nodal admittance matrix analysis has been formulated. In this work, an alternative two‐graph method is formulated, which has the advantage of providing a compact intermediate form for subsequent symbolic term generation. With a compact two‐graph representation, either a matrix method or a tree enumeration method can be employed. For completeness, the classical two‐graph theory has been extended in this paper to encompass all four types of dependent sources and all pathological elements. Illustrative examples are presented to demonstrate the principle of compact symbolic term generation by the presented two‐graph method. Copyright © 2014 John Wiley & Sons, Ltd.     

基于噪声相关特性的数学形态学消噪原理研究

结合电力信号采集中噪声的相关性理论和数学形态学基本原理,通过数值仿真详细研究了自相关噪声和随机白噪声干扰下,数学形态学滤波中关于结构元素如何选取的问题。分析指出,针对自相关噪声,结构元素的选择与噪声的周期性,最大峰值及采样率等因素密切相关。类似高频正弦噪声,通过选择合适尺度的正余弦形或三角形结构元素进行形态滤波均能取得良好的滤波效果。而对于随机白噪声而言,由于不具有自相关特性,因此并不存在类似相关噪声下的结构元素选取规律,多数情况需要通过预先的仿真或根据经验来合理选择结构元素。     

RFID Technologym - Are You Ready for It?

In this paper, the technical considerations and broad business implications of RFID are focused. The basic RFID hardware elements are tags and readers. The data exchanged between these two elements may be encrypted or processed as needed. From a technical point of view, the challenges in designing an RFID tag are many. Silicon technology can deliver the required circuit performance at low cost and high volume and efforts are made to design a system on chip (SOC) at RF frequency.     

High-order non-linear circuit elements: Circuit-theoretic properties

Highei- and mixed-order non-linear circuit elements have been introduced to provide a logically complete formulation for non-linear circuit theory. In this paper, we analyse the circuit-theoretic properties of these elements, including reciprocity, passivity and losslessness. We have derived necessary and sufficient conditions for a higher- or mixed-order n-port element to be reciprocal or antireciprocal. We have shown that under very mild assumptions, most non-linear higher-order 2-terminal elements are active and not lossless. Finally, we show that the number of lossless linear higher-order 2-terminal elements far exceeds that of the passive linear elements.     

Fault calculations using three terminal Thevenin’s equivalent circuit

The aim of this paper is to present a systematic approach of calculating fault currents due to the switching of elements or fault impedances that involve two buses and ground. Traditionally, Thevenin’s equivalent circuits are made up of two terminals suitable for calculating the current into an element connected between both terminals of the equivalent circuit. In such cases, the current entering the element is equal to the current leaving the element. So many practical cases involve elements that have a third terminal connected to ground. Tee and pi models of transmission lines are examples of such cases. Traditionally, the two terminals Thevenin’s equivalent circuit is used to tackle such problems by decomposing the three terminal element into its basic elements. The problem is then transferred to a multi element application where each element is processed once a time. This approach is cumbersome and time consuming. In this paper, a systematic approach to applying the three terminal Thevenin’s equivalent circuit to three terminal elements is proposed.     

电厂温度测量元件选择的几点建议

引对一些发电企业忽视温度测量元件精度的问题．文中建议涉及供热贸易计量的仪表或电厂中重要参数仪表应采用较高精度的测温元件，以提高电厂计量的准确度。并就铠装热电阻的检定法、铜电阻的应用价值及在DCS中取消温度中间测量环节等提出看法。