Radio frequency signal transmission on medium voltage powerdistribution lines

A series of tests measuring HF signal attenuation were performed on a de-energized 15 kV three-phase power distribution feeder. The feeder consisted of a U-shaped line measuring approximately 208 m in length with varying line geometry around the circuit. RF signals in the range of 2 to 30 MHz were injected in one phase of the feeder and the propagated responses were measured at two locations along the feeder. Tests were conducted with and without shunt power equipment (distribution transformers, arresters and capacitors) connected to the feeder. The characteristic line impedance of different line geometries was calculated by analytical means and found to be consistent with experimental results. Attenuation and characteristic impedance were found to be relatively constant at frequencies between 15 and 30 MHz with minimal influence from line geometry and power equipment placement     

Signal Propagation on Single Phase Power Distribution Lines at Power Line Carrier Frequencies

Two sets of propagation measurements were made on a 20,847 foot unenergized power distribution line in the frequency range 0 to 50 kHz. The line was configured with and without distribution transformers. From the first set of measurements a voltage transfer function was calculated for this line. In the second set of measurements the line was energized with a 25 kHz signal and the voltage, current and impedance were measured along the line. Various propagation characteristics such as attenuation, characteristic impedance, velocity of propagation, and standing wave ratios were determined from these measurements.     

一种基于电能质量分析仪测量的低压配电网线路阻抗估计方法

该文提出了一种基于电能质量分析仪测量的低压配电网线路相线以及中性线阻抗估计方法。该方法使用两台带GPS的电能质量分析仪分别安装于线路的首末端,基于同步时钟模块(GPS)实现同步对时,并利用了电能质量分析仪的4个电流通道、4个电压通道,提出同步测量线路首末端ABC三相对中性线基波电压的相量值以及ABCN四线基波电流相量值,并基于此测量值较准确估计出三相四线制低压配电网线路中性线以及相线的基波阻抗参数,为低压配电网分析,网损计算和电能质量状态获得基础参数数据。     

无线电能传输中的高频阻抗匹配特性分析

磁谐振式无线电能传输技术是基于磁谐振耦合现象利用近区磁场进行非辐射性、中距离输电的新技术。阻抗匹配技术在无线电能传输中广泛使用,用以增加传输距离,提高传输效率,使负载获最大功率。常规变压器适于在低频下作阻抗匹配,高频时磁芯容易饱和发热,降低传输效率。使用传输线原理绕制的变压器通过线间电感和电容耦合传输能量,可用于高频传输,亦可在无线电能传输系统中使用。文章分析了无线电能传输阻抗匹配原理,分析了传输线原理绕制的变压器匹配特性,使用高频变压器进行了无线电能传输的比较实验。实验结果表明高频变压器可用于无线电能传输,匹配得当时,增加传输距离的同时,可保持传输效率和最大输出电压,是提高无线电能传输性能的一种可选方法。     

Distribution factors of reactive power flow in transmission lineand transformer outage studies

The authors present a fast and accurate method to calculate a set of distribution factors of reactive power flow for transmission line and transformer outage studies. The transmission branches are broken into two categories: transmission lines and transformers. Separate formulas are derived to calculate the distribution factors of the reactive power flow. A transmission line model is developed. The reactive power flow in a line is divided into two parts: the transmission part and the loss part. Based on this model, transmission line outages were simulated by power injections which cancel the reactive power flow in the outage lines. Formulas to calculate the distribution factors of the reactive power flow are derived using the decoupled load flow characteristic, network sensitivities, and the principle of superposition. The formulas to calculate the distribution factors of the reactive power flow in transformers are also derived     

Analysis of Distribution Line Carrier Propagation Using the Bus Impedance Matrix

Distribution line carrier (DLC) is a communication system used in automated distribution systems to transmit data between the substation and certain locations on the distribution primary and secondary. Extensive DLC propagation measurements have shown that the propagation of signals on a power distribution line is difficult to predict because of the complexity and variability of distribution systems. This paper presents an efficient and comprehensive analytical tool for predicting DLC signal propagation over complex distribution systems. This paper develops a three-phase bus impedance matrix, which consists of 3×3 transfer impedance submatrices. These submatrices represent the general transfer function which relates the three-phase received voltage vector at any point of interest to any three-phase transmitted (injected) current vector at any point of interest. The method described here is an extension of the three-phase bus impedance approach used for 60 Hz power distribution.     

低压电力线载波信道阻抗测试终端的设计与应用

依据自由坐标轴阻抗测试原理,设计了低压电力线载波信道阻抗测试终端,实现了载波信道阻抗模值和阻抗相位的实时测量、数据远程传输以及主站监控计算机对信道阻抗特性的远程监控。阻抗测试终端依据主站监控计算机的控制命令,能够实现在100～500kHz频率范围内的任意5个载波频率点或单一载波频率点处,同时对A、B、C三相或某一相的循环阻抗测试,且载波频率点间的最小间隔为0.1kHz。阻抗测试范围与精度可达到(5～10Ω)±10%、(10～500Ω)±5%。本文分析了公用建筑不同季节和住宅小区冬季载波通信性能较差情况下的电力线信道阻抗测量结果,为电力线阻抗监测及改善电力线载波系统通信性能提供有力手段。     

基于微扰法的低压有源配电网故障定位方法

分布式电源（DG）接入低压配电网,使配电网潮流分布变得复杂,基于单向潮流的传统故障定位方案不再适用。提出基于微扰法进行相模变换实现含分布式电源低压配电网的故障定位方法。针对配电网三相线路参数不对称,运用微扰原理,通过构造线路参数阻抗矩阵微扰量,求出使原相互耦合的三相网络解耦成3个相互独立序网图的相模变换矩阵,实现了对不对称线路参数阻抗矩阵的解耦;在此基础上,对低压有源配电网依据区段故障前后相模变换电流故障分量的相角差值的变化,推导出判断配电网故障区段的判据,实现对低压配电网的故障定位。通过Matlab/Simulink进行了仿真分析,结果表明：该方法可以快速准确地定位出故障区段,解决了配电网络参数不对称对定位精度的影响。     

Harmonic response tests on distribution circuit potentialtransformers

Experimental data are presented that show the performances of distribution circuit potential transformers operating with nonsinusoidal waveforms. Four standard magnetic voltage transformers designed for 60 Hz power applications and rated from 7.2 kV to 20 kV were tested. Ratio correction factor and phase angle measurements were conducted at rated 60 Hz voltage with harmonic distortion levels at and below 8%. Test results indicate that potential transformers rated up to 20 kV experience errors of less than 5% at harmonic frequencies up to 3500 Hz when operating into typical induction watthour meter burdens. The phase angle response is essentially linear over the frequency range used to test the transformers, with a typical phase angle of about -10° at frequencies of approximately 3 to 3.5 kHz     

中压配电网最佳供电能力分析

针对中压配电网规划的特点,提出了一种在满足供电半径、馈线配电变压器容量限额的前提下,10 kV馈线最佳供电能力的计算方法,得出了馈线在经济运行条件下负荷密度、馈线型号、配电变压器容量等之间的对应关系。分析了各种接线方式的线路不同情况下的最佳供电能力,并以电压质量、线损率等指标对结果进行了校核。以某地区实际配电网为例,验证了该方法在评估中压配电网最佳供电能力方面的可行性。该方法可用于优化网架结构,提高配电网的可靠性和经济性,以及指导城市中压配电网的规划建设。     

一例出口的长输电线路末端的电力变压器设计

设计了一种出口的长输电线路末端的电力变压器,分析了由于上级母线和输电线路产生的阻抗压降引起的变压器电源电压变动时的计算方法,及变压器一次侧调压方式和电源波动范围、频率的关系。指出变压器设计过程中要针对具体的项目进行综合分析,合理选择变压器参数,改进变压器结构。     

适应季节性负荷的配电变压器与台区线路协调规划方法

为改善农村煤改电地区设备利用效率低的问题,并兼顾供电可靠性,提出一种适应季节性负荷的配电变压器与台区线路优化规划方法。主要思路是建立配变间低压联络线,根据季节性负荷特点,通过联络线开关状态变化,转换运行方式,使部分配变低负荷季节退出运行。以综合费用最小为目标构建配电变压器网络双层规划模型,上层采用Voronoi法规划配电变压器,下层采用Prim算法规划低压供电线路,并结合遗传算法进行优化求解。最后,通过对典型供电区域进行配变规划验证了该方法的可行性,并且能够降低配变损耗,提高供电的可靠性和经济性。     

一种配电变压器零序阻抗计算方法

本文中作者结合配电变压器实际运行情况,提出了一种配电变压器零序阻抗计算方法,在利用配电变压器运行数据的基础上,建立了含零序阻抗待求量的非线性方程组。     

Distribution Transformer Winding Losses Due to Nonsinusoidal Currents

Increased transformer winding losses are an important consideration in determining the overall impact of harmonic currents in a power system. Frequently, losses due to harmonic currents are assumed to vary with the square of frequency. The purpose of this paper is to compare winding loss calculations from a finite element method with measured losses in single phase distribution transformers and to test the principle of superposition of harmonic losses due to nonsinusoidal currents. The results confirm both the finite element method and the principle of superposition. Furthermore, it is shown that, due primarily to inaccuracy in measuring 60 Hz eddy current losses, application of the commonly accepted frequency squared rule can yield overly pessimistic loss predictions for typical power system harmonic frequencies.     

自适应负荷型配电变压器设计

自适应负荷型配电变压器具有自适应负荷功能和性能特点,可在不切断负荷的情况下,根据系统电压和负荷实际情况,实现变压器电压分接头调整、额定容量运行方式的自动切换、在线负荷换相以及分相无功补偿。阐述了自适应负荷型配电变压器的功能架构设计;解析了其在线负荷换相、有载调容、分相无功补偿和有载调压等功能实现控制原理;给出了动作定值设定方法;建立了功能实现仿真试验模型。经仿真分析,验证了自适应负荷型配电变压器较普通配电变压器具有明显功能优势,适用于负荷季节性强、年平均负载率低、空载损耗占比高、用户端电压合格率和功率因数偏低的农村配电网中,可提升配电台区经济运行水平,保障用户供电质量,降低配电网运行损耗,充分发挥配电层级的节能减排作用。     

基于测量阻抗变化的含IIDG配电网保护研究

含IIDG配电网,由于电力电子器件的限流控制以及不同的控制策略,会导致传统保护失效。因此提出了一种通过采用故障前后线路两端测量阻抗幅值的差值变化和线路两端测量阻抗相角差变化为判据的含IIDG配电网保护方案,该方案可以实现配电网区内外故障的有效识别,实现保护的正确动作。方案的有效性通过PSCAD/EMTDC仿真软件进行了验证。     

一种含分布式电源的配电网三相潮流混合计算方法

针对现有配电网三相潮流计算方法的不足,提出了一种新的含分布式电源的配电网三相潮流混合计算方法。分析了配电网中相关元件的特点,建立了配电线路、配电变压器和负荷的三相数学模型。对4种不同类型分布式电源节点的处理方式进行了分析,采用前推回代法和牛拉法的混合计算方法建立了三相潮流计算模型。采用回路阻抗矩阵法来计算三相电压差,解决了单相潮流计算方法的适用性问题,采用以节点电压的收敛性作为潮流计算程序迭代与否的控制目标,可直接求取电压值,迭代计算简洁高效。最后,以包含分布式电源的IEEE 33节点网络模型和山滩变某10 kV配电线路为例,验证了该混合计算方法的收敛性与高效性。     

中性点不接地配电网电容电流实时测量新方法

提出了一种实时测量中性点不接地配电网电容电流的新方法———单频率测量法,即从电压互感器开口三角侧注入一个恒定的电流信号,测量开口三角侧电压和二次星形侧相电压。根据注入的电流信号和测出的电压信号,计算出配电网对地电容值和电容电流值。该方法完全避免了电压互感器短路阻抗和注入信号频率选取组合对测量结果的影响。经理论推导和模拟实验验证,该方法不影响配电网正常运行,具有安全、简捷、准确等优点。     

电力变压器有源谐波模型

建立适当的电力系统元件谐波模型是电力系统谐波分析的基础,章总结了电力变压器谐波模型的已有研究成果,推导了单相变压器完整的有源谐波模型,然后将电力变压器的谐波建模问题归结为激磁电流的计算,详细介绍了单相变压器激磁电流的计算和谐波分析方法。     

基于配电网低载线路合并运行的降损分析研究

线损率是配电网经济运行的重要考核指标之一,降低线路损耗对配电网经济运行具有重要意义。本文提出了将供电范围邻近的低载线路合并运行、减少台区运行数量的供电模式,分析了该运行模式在满足配电网运行可靠性的前提下降低线路损耗的可行性以及线路合并运行供电模式的应用前景。研究结果表明,在不影响供电可靠性的前提下,该模式对于降低线路损耗具有较为明显的效果。