调整不平衡电流并补偿功率因数的新型节能设备

本文介绍的这种新型节能设备能够把配电网三相不平衡电流调整到平衡状态的同时,把三相的功率因数都补偿到“1”。其主要方法是根据电路中已有的阻抗量借助智能化的管理与计算将适当的电容量加到三相电路中,从而达到既提高电路的功率因数又平衡电路中的三相电流。文章以实例阐述了基本原理。仿真实验和挂网运行实践的真实数据对其工作原理的科学性、节能效果(功能)的确定性以及性能指标的可靠性提供了有力的肯定性证实。该新型节能设备目前已经应用于辽宁省的沈阳、大连、大石桥、康平等城乡结合部电网和农村电网中并显现出良好的节能效果和可靠的性能质量。     

同相供电补偿电流实时检测方法

平均功率法同相供电补偿电流检测,需要积分一个周期才能得出检测结果,存在实时性差的缺点,且受电网电压畸变影响。提出了两种补偿电流检测方法:有延时的两相构造和无延时的两相虚拟。通过理论分析和仿真结果证明,两种方法都能达到对同相供电系统补偿电流的实时检测,平衡三相,消除三相谐波及无功电流。后者算法简单,动态跟踪速度快,检测精度高。     

同相供电补偿电流实时检测方法

平均功率法同相供电补偿电流检测,需要积分一个周期才能得出检测结果,存在实时性差的缺点,且受电网电压畸变影响.提出了两种补偿电流检测方法:有延时的两相构造和无延时的两相虚拟.通过理论分析和仿真结果证明,两种方法都能达到对同相供电系统补偿电流的实时检测,平衡三相,消除三相谐波及无功电流.后者算法简单,动态跟踪速度快,检测精度高.     

Online algorithm for removal of decaying DC-offset from fault currents

This paper presents an efficient method for removing exponentially decaying DC offset from fault currents. Instantaneous value of the actual exponentially decaying DC offset is calculated by integrating the input signal. The DC component is removed by subtracting the DC value at each sampling instant. The Discrete Fourier Transform (DFT) is applied to the result to extract the phasor of the fundamental component. Different transient signals are investigated. The results show that the proposed method is accurate and easy to implement.     

Π模型电容电流补偿的同塔四回线电流差动保护

分析了超高压同塔四回线长距离输电线路分布电容对传统电流差动保护的影响。在此基础上,考虑同塔四回线相间及线间的电磁耦合,建立对应频域及时域下的同塔四回线12序(模)分量Π型等值电路模型,并基于各序(模)量等值电路分别提出频域及时域电容电流补偿方法。对无电容电流补偿,频域相量电容电流补偿及时域电容电流补偿等不同电流差动保护方案动作性能进行对比,结果表明在不同运行条件下采用时域补偿具有更佳的保护性能。     

On-line diagnostics of high-voltage bushings and currenttransformers using the sum current method

Experience with the application of the sum current method to on-line diagnostics of high-voltage bushings and current transformers is presented. The method and analysis are described along with field experience obtained at fourteen substations, comprising 56 sets of (three) bushings and current transformers. The influences of temperature, humidity and changes in more than one bushing are discussed     

电动机无功功率就地补偿实践

介绍了使用低压电力电容器对电动机无功功率进行就地补偿的实践经验。叙述了试点区补偿用电容器的安装情况,安装方式,电容器容量的确定,安装位置及接线等。用实测数据说明这一措施取得降损节能的明显效果,提出了实施这一措施需要注意的问题。     

Correction of current transformer distorted secondary currents dueto saturation using artificial neural networks

Current transformer saturation can cause protective relay misoperation or even prevent tripping. This paper presents the use of artificial neural networks (ANN) to correct current transformer (CT) secondary waveform distortions. The ANN is trained to achieve the inverse transfer function of iron-core toroidal CTs which are widely used in protective systems. The ANN provides a good estimate of the true (primary) current of a saturated transformer. The neural network is developed using MATLAB and trained using data from EMTP simulations and data generated from actual CTs. In order to handle large dynamic ranges of fault currents, a technique of employing two sets of network coefficients is used. Different sets of network coefficients deal with different fault current ranges. The algorithm for running the network was implemented on an Analog Devices ADSP3101 digital signal processor. The calculating speed and accuracy proved to be satisfactory in real-time application     

An algorithm for discrete optimal power flow

This paper presents a new algorithm to solve an optimal power flow problem which can take into consideration the discrete nature of some facilities in power systems. The optimal power flow problem is formulated as a nonlinear mixed-integer programming problem in which the number of transformer taps and the number of shunt capacitor units and reactor units are treated as discrete variables. This paper attempts to solve such a large-scale nonlinar mixed-integer programming problem by some effective programming techniques. The optimization procedure of the algorithm is that the nonlinear mixed-integer programming problem is linearized iteratively and solved by an approximation method for linear mixed-integer programming. A fundamental feature of the algorithm is that it can guarantee a solution which is discrete, feasible and near-optimal. The validity and efficiency of the algorithm is demonstrated by the numerical results of real-scale optimal power flow problems.     

一种实用的高精度频率测量方法

提出了一种实用的高精度频率测量方法,能够精确测量电力系统的基波频率。结合电压过零点测频法测得的频率,对原固定采样频率下的采样序列采用拉格朗日线性插值法抽取新的采样序列,最终利用傅氏算法测得高精度频率。该方法不仅消除传统傅氏测频时的频谱泄露及栅栏效应,而且可以很好的抑制谐波的影响。测试结果证明该方法实现简单、准确,能够满足电力系统对频率测量精度及实时性的要求。     

高压并联电容器补偿成套装置的二次保护

详细论述了高压并联电容器补偿装置的保护和电容器组的保护,给出了开口三角电压保护、不平衡电流保护、过电压保护、失压保护等的保护整定计算的具体方法,并列举了典型的二次保护方式。     

变电站二次系统防雷保护初探

变电站二次设备的防雷保护是一个新的课题．其设计思想强调以电子信息系统为保护核心,为被保护设备构建一个均压等电位系统,并通过各级电涌保护器．逐级把雷电流泄放入大地。广东省广电集团有限公司汕尾供电分公司在对110kV汕尾变电站进行自动化改造的工程实践中．根据以上设计原则并结合实际情况对变电站二次设备防雷进行选型设计,提高了系统的运行安全性和可靠性。     

农村配电网常用无功补偿方式

针对农村配电网末端电压合格率和功率因数较低的现状,分析了农村配电网络结构与负荷特点,对目前农网中常用的三种无功补偿方式及其适用范围进行了总结。     

无功补偿电容器运行特性参数选取

1电力电容器及其主要特性参数电力电容器是无功补偿装置的主要部件。随着技术进步和工艺更新,纸介质电容器已被自愈式电容器所取代,自愈式电容器采用在电介质中两面蒸镀金属体为电极,其最大的改进是电容器在电介质局部击穿时其绝缘具有自然恢复性能,即电介质局部击穿时,击穿处附近的金属涂层将熔化和气化并形成空洞,由此虽然会造成极板面积减少使电容C及相应无功功率有所下降,但不影响电容器正常运行。自愈式电容器主要特性参数有:额定电压、电容、无功功率。1.1额定电压GB 12747-1991《自愈式低电压并联电容器》第3.2条规定“电容器额定…     

An incremental measurement placement algorithm for state estimation

Measurement configuration and redundancy significantly impact the quality of state estimation solutions. Practical and efficient algorithms are needed to suggest additional measurement locations in order to increase local redundancy and strengthen network observability. In this paper, an incremental measurement placement algorithm is proposed to enhance the quality of state estimation solutions. The algorithm identifies buses with low accuracy based on state estimation error variances. A list of candidate measurements is suggested to reduce these variances. Certain heuristics are applied to discourage introduction of the possible leverage point measurements. The algorithm has been implemented in the PG&E EMS environment and tested using the real-time data     

An error correction algorithm for stochastic production costing

A theoretical approach is presented for calculating the error involved in the solution of stochastic production costing problems using the method of cumulants. It is proposed to use this calculated error in an algorithm for obtaining an improved stochastic approximation of the equivalent-load-duration curve. The results show that of the three series that can be used for stochastic approximation, namely, the beta, the Gram-Charlier, and the Laguerre, the beta gives the best results. All three methods, however, give unacceptable errors in the approximation of the expected unserved energy. Another method is proposed that approximates the error between the beta curve and the actual curve using the Fourier-Chebyshev expansion, which is used to develop a better stochastic approximation. Results obtained using practical system data indicate that this method gives much better results than the three methods discussed above     

基于固定时间一致性算法的孤岛微电网分布式容错二次控制策略

随着微电网信息侧和物理侧的耦合日益紧密,软件密集型控制器和电力电子设备的大规模应用增加了微电网遭受攻击和故障的可能性,从而影响微电网的稳定运行。为此,针对孤岛交流微电网控制通道中潜在的执行器故障和传感器故障,提出了一种基于固定时间一致性算法的分布式容错二次控制策略。首先,建立了同时计及执行器故障和传感器故障的下垂控制模型。其次,分别设计了上层分布式一致性控制算法和下层本地容错控制算法,分析了控制器对未知故障的抑制机理,从理论上证明了所提分布式容错二次控制策略的固定时间收敛特性,并进一步观测了传感器故障信号的波形。最后,算例仿真结果验证了所提控制策略的有效性。     

一种适用于隔离开关的边缘提取算法

随着视频监控技术成为变电站自动化及电网自动化的一个重要手段,对隔离开关的视频监控图像处理算法的研究也提上了一个更高的层次.在分析经典边缘检测算子的基础上,针对输电线高压隔离开关的具体图像特征,提出了一种适合其自身特征的边缘检测算法,该算法从主动识别方面考虑,只处理局域图像,大大减少了处理量,提高了处理速度.最后,对GW17-550D型高压隔离开关的合状态和GW22-12型隔离开关的开状态分别采用经典算法和该文的算法进行了仿真,结果表明本文的方法更满足实际要求.     

一种改进的三电平空间电压矢量调制算法

提出了一种新的三电平空间电压矢量调制算法,该算法通过直接对三相参考电压进行比较从而判断出合成参考矢量所在区域,并基于伏秒平衡原理计算得到各个标准矢量的作用时间.通过与传统算法进行比较可以看出,提出的算法与传统算法控制效果相同,但其不需要进行正余弦计算,能够大量节省计算时间.最后通过实验验证了该算法的有效性.     

An improved genetic algorithm for generation expansion planning

This paper presents a development of an improved genetic algorithm (IGA) and its application to a least-cost generation expansion planning (GEP) problem. Least-cost GEP problem is concerned with a highly constrained nonlinear dynamic optimization problem that can only be fully solved by complete enumeration, a process which is computationally impossible in a real-world GEP problem. In this paper, an improved genetic algorithm incorporating a stochastic crossover technique and an artificial initial population scheme is developed to provide a faster search mechanism. The main advantage of the IGA approach is that the “curse of dimensionality” and a local optimal trap inherent in mathematical programming methods can be simultaneously overcome. The IGA approach is applied to two test systems, one with 15 existing power plants, 5 types of candidate plants and a 14-year planning period, and the other, a practical long-term system with a 24-year planning period