雷电通道基底电流函数半解析逼近研究

雷电瞬态电磁现象的研究中,Heidler函数已成为通道基底电流的标准函数之一。由于Heidler函数的Fourier变换不存在解析表达式,数值计算时需采用快速傅氏变换技术进行频域分解,这极大地增加了计算时间。针对此问题,提出Heidler函数的半解析逼近表达式。其在时域中将雷电通道电流表示成幂指数函数的线性组合,推导出Fourier变换的半解析计算结果。该方法可推广应用于任意阶数的Heidler函数及由其衍生的雷电流函数。     

Investigation on the transformation of time domain spectroscopy data to frequency domain data for impregnated pressboard to reduce measurement time

The accuracy of different transformation methods for time domain dielectric response data to frequency domain and their limits are studied. First an approximated analytic function is considered, second an extended Debye model for the dielectric behavior of impregnated pressboard. The last method is a numerical integral form and Fast Fourier Transform. Hamon approximation relates time domain data at t to frequency domain data at f=0.1/t and gives the results by sole measurement of polarization current. Dielectric diagnosis of high voltage apparatus can be done by using Hamon approximation in minimum duration. All transformation methods show similar results and they are analyzed in order to demonstrate the limits of the methods.     

频域逼近优化的开关电流电路小波变换方法

提出了一种频域逼近优化的开关电流电路小波变换方法。利用小波函数幅度响应和相位响应信息,并考虑滤波器稳定性,设计小波基滤波器频域逼近优化模型,模型可采用常规优化算法求解。基于第二代开关电流积分器电路,构造一阶节和双二阶节基本电路模块。以五阶高斯小波基为例进行优化逼近,对逼近获得的小波基滤波器传递函数进行级联分解,并采用开关电流基本电路模块进行小波基电路综合。分析表明,五阶高斯小波逼近时域均方误差仅为2.883×10-4,频域均方误差仅为5.061×10-4。仿真结果表明,电路具有逼近效果好、小波尺度可调谐、电路灵敏度低等特点。     

在地磁感应电流作用时分析和计算电力变压器特性的一种新方法--时域和频域法

提出了在地磁感应电流(Geomagnetically Induced Current)作用时,分析和计算电力变压器特性的一种新方法.作者将时域中变压器的等效磁路法同频域中变压器的等效电路法有机地结合在一起,成功地用于分析和计算GIC作用时三相电力变压器的特性.文中给出了非线性模型、求解原理.仿真和实验结果证明了本文的方法是正确的.     

A system for the measurements of lightning currents at the Säntis Tower

The paper presents the characteristics of a system suitably developed to measure lightning current waveforms on the Säntis Tower in Switzerland. The paper first describes the configuration of the system then presents the characteristics of the measurement equipment, in terms of bandwidth and accuracy, inferred by means of experimental tests. Finally, we present and discuss examples of waveforms measured using the system.     

无死区测频方法

本文根据对无死区连续测频的实用要求,介绍了无死区计数器的基本原理和几种易于实现的用法,并对其性能进行了分析。     

结构体系可靠度分析中二维标准正态分布函数的近似计算

二维标准正态分布函数在结构体系可靠度分析中经常被用到,但它的计算一般涉及数值积分,工程不便应用。本文根据概率乘法定理,利用以条件数学期望和方差为参数的一维正态分布近似代替原来的条件分布,从而得出计算二维标准正态分布函数值的近似公式。通过数值积分结果比较表明,近似公式计算简单,应用方便,精度较好。     

应用电站设备宽频特性的过电压在线监测装置

过电压的监测和分析对现代电力供电系统有极其重要的意义.通过分析比较国内外现有过电压在线监测装置的特点,提出了一种新型的利用设备宽频传输特性的过电压在线监测方法,其原理是将电压互感器(TV)、二次电缆和分压器等二次设备看作相互级联的二端口网络,通过有理甬数逼近建立了其传输参数模型;基于该模型,可由二次设备输出端口的电压信...     

Application of artificial neural network methods for the lightning performance evaluation of Hellenic high voltage transmission lines

Feed-forward (FF) artificial neural networks (ANN) and radial basis function (RBF) ANN methods were addressed for evaluating the lightning performance of high voltage transmission lines. Several structures, learning algorithms and transfer functions were tested in order to produce a model with the best generalizing ability. Actual input and output data, collected from operating Hellenic high voltage transmission lines, as well as simulated output data were used in the training, validation and testing process. The aims of the paper are to describe in detail and compare the proposed FF and RBF ANN models, to state their advantages and disadvantages and to present results obtained by their application on operating Hellenic transmission lines of 150 kV and 400 kV. The ANN results are also compared with results obtained using conventional methods and real records of outage rate showing a quite satisfactory agreement. The proposed ANN methods can be used by electric power utilities as useful tools for the design of electric power systems, alternative to the conventional analytical methods.     

放电通道对离子背景的选择性

用实验方法研究了正、负离子背景对放电路径的影响。采用了两种不同的实验方法观测研究了不同离子背景对放电进展路径影响的特点、程度及规律性。发现放电路径具有选择负离子背景而回避正离子背景的特点以及用预置离子背景控制放电路径的可能性。这一现象有可能在防护直击雷方面获得应用。     

Frequency domain modelling of random wound motor windings for insulation stress analysis

The use of conventional low voltage induction motors fed by pulse width modulated (PWM) inverters has begun to present important problems. These waveforms consist of steep-fronted pulses having very short rise times (about 100 ns in modern IGBT bridges) and high frequency repetition rates (up to 20 kHz) whose immediate consequences are additional electrical stresses in an induction motors insulation system. In this paper a frequency domain model for the analysis and characterization of the internal voltage distribution in random wound coils is presented. The model allows voltage prediction in time domain when an inverse fast Fourier transform (FFT) transformation is performed, and requires only a few frequency domain impedance measurements. This methodology will be useful for accurately predicting the voltage distribution in motor windings during the design stage, and reducing the risk of premature failure in motor insulation. Experimental and theoretical results are presented and compared and model effectiveness using different approximations is studied.     

特高压线路的避雷线保护范围设计

目前,在特高压线路的避雷线保护范围设计中,仍采用传统的不考虑特高压导线电压影响的方法,可能使特高压线路避雷线的实际保护范围满足不了高可靠性防雷设计的要求。为了解决这一问题,在特高压线路的避雷线保护范围设计中,考虑特高压导线电压的影响,提出以特高压导线的最小对地空气间隙距离为半径,构成特高压导线的等效绝缘截面,并设计该等效绝缘截面位于避雷线的保护范围之内。计算结果表明,若不考虑特高压导线电压的影响,特高压线路的避雷线保护范围将存在严重的安全隐患。     

基于双窗全相位FFT双谱线插值的谐波和间谐波分析算法

在利用传统快速傅里叶变换进行谐波和间谐波分析时,由于非同步采样或非整周期截断,容易影响谐波和间谐波的检测精度.本文提出了一种基于双窗全相位快速傅里叶变换双谱线插值的电力谐波和间谐波分析算法.该算法利用双窗全相位快速傅里叶变换主谱线相位值来估计信号初相位,选择紧邻峰值频点的左右两根谱线进行频率和幅值的插值校正,结合多项式...     

继电保护和故障录波管理信息系统的研制与应用

介绍了微机继电保护信息管理和故障录波曲线分析的应用系统,主要阐述了系统的网络结构、软件模块及其流程算法的设计和研发过程,解决微机保护信息的采集、处理,并在此基础上所进行的故障录波曲线谐波分析和矢量分析,实现了继电网保护信息自动化管理。     

Improvement of sensorless control performance for IPMSM by suppression of harmonic current using Fourier transform and repetitive control

In the case of the sensorless control for the PMSM that estimates position and velocity from EMF using a model of synchronous motor with the voltage and current, it is desirable for voltage and current to be perfect sine waves. However, in reality, voltage and current contain various harmonic components, which negatively affect the estimation ability of the sensorless control. In this paper, we propose a method of improving the sensorless control performance for the IPMSM by suppression of harmonic component in current control loop of the vector control using Fourier transform and repetitive control. To suppress harmonic components, compensation signals are acquired using Fourier transform and repetitive control, and feedforward control is implemented with the acquired compensation signals. To evaluate the proposed system, the sensorless control system for the IPMSM is considered as an example. The system is constructed on the basis of the extended EMF disturbance observer, and the improvement potential of the sensorless control performance is demonstrated. The effectiveness of the proposed method is confirmed by experimental results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 76–86, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20095     

矢量网络分析仪时域功能分析

矢量网络分析仪采用时频变换及时域选通方法来获得待测器件真实的频率响应。文中给出上述方法理论依据和实现步骤,介绍了不同窗函数对变换结果的影响和基于Chirp-Z变换的时域测量算法,推导出时域选通门的数学表达式,解释了理论结果出现失真的原因。并采用Visual Basic结合Measurement Studio语言编写相关软件实现时域测量功能,最后给出实际测量和变换结果,对结果进行分析后提出下一步的工作方向。     

电流互感器10%误差曲线的作用及其绘制方法

阐述了10%误差曲线的的定义、影响因素、利用伏安特性求取10%误差曲线的原理以及10%误差曲线的绘制方法,结合实例介绍了误差校验过程,并提出了减小误差的具体措施。     

Inclusion of the frequency effect in the lumped parameters transmission line model: State space formulation

The objective of this paper is to include the frequency dependence of the longitudinal parameters in the lumped parameters line model. The distributed nature of the transmission line was approximated by a cascade of π circuits and the frequency effect was approximated by a rational function which was synthesized by an equivalent circuit. Then, the equivalent circuit was inserted in each π circuit of the cascade. After that, the currents and voltages along the line were described in the form of state equations. This way, it was possible to obtain a formation rule of the state matrices lumped parameters model taking into account the frequency dependence. To confirm the validation of the state matrices obtained, the lumped parameters representation of frequency-dependent lines was used to represent a single-phase line and a three-phase line. The simulations were carried out using state space techniques and an electromagnetic transient program (EMTP) (in this case, the cascade was inserted in the EMTP). It is observed that the simulation results obtained with state space representation are in agreement with those results obtained with EMTP.     

主变差动保护功能校验分析与应用

讨论了影响主变差动保护的主要因素及消除方法,并重点分析主变差动保护校验方法。该方法是在试验中采用在各侧加三相电流来实现的,并通过两组实验数据准确计算出比率制动系数,因此,该方法在现场调试主变差动保护有一定的指导作用。     

圆筒内壁温度的推算方法

本文给出了一种根据圆筒外壁温度随时间的变化规律计算内壁温度变化规律的方法。采用傅里叶变换与逆变换，可建立内壁温度与外壁温度之间的数学关系式；为了避免计算过程中误差的放大，采用频域的数字滤波技术滤掉内壁温度频谱中的高频分量，最终得到合理的内壁温度．这种方法可以用来为汽包或管道的热应力及热疲劳研究计算内壁温度边界条件。