双层土壤中组合接地棒接地电阻的新解释公式

基于等值土壤电阻率的概念和已提出的双层土壤中单根接地棒接地电阻的解析公式,导出了双层土壤中N根组合接地棒接地电阻的解析公式。验证计算结果表明：新公式与计算机数值算法结果吻合较好。     

Calculation of earth resistance for a deep-driven rod in amulti-layer earth structure

In order to obtain an equation for calculating the earth resistance of a deep-driven rod in a horizontally stratified multilayer earth, expressions for the potential in such a structure are derived and evaluated with reference to previously established expressions for the two-layer model. In addition, when a series of numerical test data (earth parameters) is applied to the obtained equation, the behavior of earth resistance for a deep-driven rod in regard to the multilayer problem is revealed through examination of the calculations. The eventual purposes of the derived equation is to help the grounding designer obtain the earth resistance required by making it possible to more accurately estimate the depth of boring or the length of a rod even in a multilayer situation     

三层土壤中垂直棒接地电阻的解析计算方法

基于等值土壤电阻率的概念，导出了三层土壤中垂直棒接地电阻解析计算公式。验证计算结果表明：解析公式与计算机数值计算法结果相比较，计算误差小，具有实用价值。     

Resistance to ground of combined grid-multiple rods electrodes

The resistance to ground of a wide set of square and rectangular grid electrodes combined with multiple rods, buried in uniform and two-layer soils, has been analyzed using available exact computer software. Based upon the results of this analysis, analytical, expressions and graphs for electrodes resistance to ground are provided, appropriate for practical application in substation protection     

Maximum step voltages of combined grid-multiple rods groundelectrodes

Expressions are suggested for assessing the maximum step-voltages and associated parameters of combined grid-multiple rods ground electrodes buried in uniform soil. The expressions proposed are successfully verified by comparison to exact computer calculations performed for a wide set of square and rectangular ground grids reinforced by ground rods distributed around the grid perimeter and within the grid     

绝缘电阻与接地电阻测试系统的设计

本文介绍了绝缘电阻和接地电阻测试的基本原理,设计了符合IEC6101标准的绝缘电阻、接地电阻测试系统,系统由程控电源、接地电阻测试回路、绝缘电阻测试回路、信号采样、调理电路和控制器系统等部分组成.实验表明,系统性能稳定,重复性好,能实现测量、控制、显示一体化.     

煤矿电网含并联供电线路的小电流选线

针对煤矿电网并联供电线路发生单相接地故障时保护易误动、拒动,并难以断定是并联线路中的哪一条发生故障,提出了基于相间电流差的选线方法.该方法利用以故障相为基准的故障线路相间电流差等于单相接地电流,而非故障线路的相间电流差为零作为判断依据,通过计算比较选出相间电流差最大的线路,亦即故障线路.PSCAD仿真及动模实验表明,该方法能准确判断出故障线路,且在并联线路某支路发生单相接地故障时也能准确选出,保护差值大,不受故障相接地相位及接地方式影响,抗干扰能力强.     

A practical method for the interpretation of earth resistivity dataobtained from driven rod tests

Simple semiempirical expressions for the ground resistance of a single rod driven in two-layer soil are suggested. The expressions have served as the basis for a method of interpreting driven-rod test data to estimate soil parameters. The approach is demonstrated for several sets of computer and field experimental data     

基于并联虚拟电阻的多逆变器控制策略

功率均分与环流抑制是微电网中逆变器并联控制的关键问题。针对线路阻抗差异造成的系统功率均分精度低下及系统环流等问题,提出一种基于并联虚拟电阻的多逆变器控制策略。通过对各逆变器的电压跟踪系统进行设计,利用虚拟支路电流对内环电流参考值进行强制修正,从而改变各逆变器的等效连接阻抗,实现系统功率均分精度的提高及环流抑制。最后,结合逆变器等效输出阻抗的伯德图,对电压跟踪系统中的相关控制参数进行了选择。在Matlab/Simulink中搭建了仿真模型,验证了新方法的有效性。     

深圳地区变电站接地电阻计算中分流系数的探讨

深圳地区变电站的特点是系统短路电流大,占地面积小,大多数变电站没有外引接地网的条件,接地电阻不能满足有关技术标准的要求、要解决这个问题,就要充分利用避雷线和进线电缆外护套的工频分流作用．减小在接地故障时接地网的入地电流、为此,阐述了入地电流的概念,对输电线路架空避雷线、电缆线路及架空电缆混合供电线路的分流系数进行了探讨和计算、最后,提出了设计上选取分流系数的方法和工程上应采取的措施。     

Mutual coupling between finite lengths of parallel or angledhorizontal earth return conductors

Mutual coupling between earth return current and potential test conductors used during stage tests of a grounding system is discussed. The coupling is a source of significant error in measuring grounding potential and grounding system impedance. Mutual impedance formulae are presented for correcting mutual coupling errors resulting from any length of paralleled or angled horizontal ground return current and potential conductors. The formulae are an extension of the complex image plane approximation of J.R. Carson's (1926) formula for infinitely long parallel conductors     

三极管并联使用的分析

从目前空调实际应用的角度,分析了ULN2003驱动电路两路并联运行时可能造成电流不均衡的各种因素。介绍了选择三极管并联运行的思路和原则,提出了保证三极管并联可靠运行的设计方法。     

大型地网接地电阻数值计算的初步研究

从电磁场理论出发,应用矩量法求出大型地网的电荷分布和电容,从而导出接地电阻计算的一种新方法,并编制出计算机程序,算例结果证明了本方法的有效性。     

A new principle for high resistance earth fault detection duringfast power swings for distance protection

The combined effects of a high impedance ground fault condition and a fast power swing condition cause the apparent impedance `seen' by power system distance protection schemes to vary over a wide range. Previous research work has shown that the detection and location of high impedance faults during power swings is very difficult. A new principle for high impedance fault detection during fast power swings is presented which overcomes these deficiencies. This method forms a part of a complete power swing relaying scheme and can be implemented on standard relaying hardware. Results are presented based on extensive simulation studies carried out on a typical 400 kV transmission system, using the Electromagnetic Transient program (EMTP)     

并联逆变器改进下垂控制策略分析

逆变器作为分布式电源和交流母线的连接载体,能够将分布式电源的能量输送至大电网,为了使逆变器输出电能满足供电需求,需要采取相应的控制策略。针对微电网线路阻抗不匹配,传统下垂控制功率分配失衡的问题,提出了一种基于动态虚拟感抗的改进下垂控制策略,该策略无需获取线路阻抗信息,用一种新的方法计算动态电感,优化线路阻抗比以及提升功率分配精度,同时减小电压差、抑制环流,降低了系统复杂性。在Matlab/Simulink中搭建系统模型,对比不同控制策略下的仿真结果,验证了该策略的有效性。     

并联变压器经济运行方式分析

阐述了基于变压器临界功率计算的变压器经济运行方式分析的基本原理,重点对双绕组和三绕组变压器的有功功率损耗进行了分析,对不同运行方式下变压器的有功功率损耗进行了比较。     

Numerical calculation of AC substation grounding systems buried in a vertical multilayered earth model by higher‐order basis function

To study the accuracy of numerical simulations for an AC substation grounding problem embedded in a vertical multilayered earth model, this paper proposes a novel algorithm combining the rapidly convergent one‐dimensional Galerkin's BEM with higher‐order basis functions on the basis of the quasi‐static electric field theory. General analytical formulas for the mutual impedance between any pair of short line conductors are also derived to accelerate the numerical integration. These formulas can work in not only complex space but also real space because of our application of the quasi‐static complex image method, which is different from the contribution of other earlier scientists, whose formula can work just in real space. The algorithm can be used to simulate and analyze any grounding system, including those incorporating a floating grid located anywhere in the earth model. Copyright © 2011 John Wiley & Sons, Ltd.     

On the calculation of resistance of the multiple driven rod electrode

Expressions for the resistance of symmetrical multiple driven rod electrodes are derived using both the conceptually correct equal potential condition and the approximate equal charge or average potential method. Computed results for several such electrode systems of practical dimensions are presented, allowing a comparison of the two methods. A general expression for the resistance of a non-symmetrical bed of driven electrodes is also derived.     

变频器驱动异步电机振动频谱特征分析

为提出一种更加有效的电机振动抑制算法,对电机振动频谱特性进行讨论.介绍了异步电机调速系统振动数据采集单元以及不同运行状态下的电机振动数据采集,给出了调压器调压和变频器变频调速2种情况下不同转速的电机振动频谱图和转速谱图.通过这些谱图,分别对电机振动特征、变频器载波频率对电机振动特征的影响进行了对比分析.谱图分析表明,采用变频器驱动异步电机时,一阶转频引起的强迫振动与自由振动波形会发生畸变,且电机振动峰值增大.随着变频器载波频率的增加,电机振动幅值将显著降低.变频器引入的高阶振动谐波转矩使得电机的振动特征更加复杂.电机振动频谱特征分析为电机振动抑制算法设计与算法评价提供了基础.     

超市用多机并联变频机组运行分析

节能减排成为当前社会发展的主题,超市制冷设备的节能越来越受关注。常用的超市半封闭活塞压缩机组为了节能开始使用变频技术,本文分析了利用交流变频技术调节压缩机电机的转速,以调节多机并联活塞机组的能量的精确输出,来适应超市冷量负荷的大幅变化,从而达到节能的效果。对实际的超市制冷机组变频与工频运转的能耗、系统稳定性进行了分析,对于超市用多机并联活塞机组,普通机组变频后的实测节能效果一般在3％-17％,机组的原来可调节能级数越多,变频后的节能效果越不明显。制冷机组可以通过变频的合理设计使设备投资减少,运行能耗减戮