An Innovative Decaying DC Component Estimation Algorithm for Digital Relaying

We propose a new decaying dc component estimation algorithm for digital relaying. Fault currents tend to include a dc decaying component. This component decreases the accuracy and speed of the protection relay operation. The proposed algorithm can estimate and eliminate the dc decaying component from fault current signals after one cycle from the fault instant. Also, it can be applied to a conventional discrete Fourier transform to calculate phasor quantities of fault currents in a digital protection relay. In the proposed algorithm, the dc decaying magnitude and time constant are estimated exactly by integrating fault currents during one cycle. The dc decaying component is eliminated by subtracting the dc value at each sampling instant. To verify the performance of the proposed algorithm, we performed a dc component estimation test and distance protection test using PSCAD/EMTDC. The results of the PSCAD/EMTDC simulation showed that the proposed algorithm can estimate dc components exactly from fault currents and can be applied to digital protection relays for phasor extraction.      

Development and hardware implementation of a reliable protective relay data acquisition system

This paper proposes an intelligence based protective relay data acquisition system to correct current transformers and capacitive voltage transformers secondary waveform distortions. The protective relay data acquisition system receives voltage and current signals from current transformers and capacitive voltage transformers and prepares the inputs to the main board after some pre-processing. Current transformers and capacitive voltage transformers provide instrument level current and voltage signals to meters and protective relays in high voltage and extra high voltage systems. The accuracy and performance of protective relays in high voltage and extra high voltage systems are directly related to steady state and transient performance of current transformers and capacitive voltage transformers. Current transformers saturation and capacitive voltage transformers transient could lead to protective relay mal-operation or even prevent tripping. The key of the proposed scheme is to use artificial neural network to achieve the inverse transfer functions of current transformers and capacitive voltage transformers. Simulation studies are preformed and the impacts of changing different parameters are studied. Performance study results show that the proposed scheme is accurate and reliable. The proposed algorithm has also been implemented and tested on a digital signal processor board. Details of the implementation and experimental studies are provided in the paper.     

电子式互感器合并单元的快速数据处理

结合数字化变电站对计量、保护等功能的特定技术要求,分析了电子式互感器应用中的关键问题,在此基础上阐述了数字化变电站中合并单元的数据处理功能的实现方法。文章讨论了采用Rogowski线圈的电子式电流互感器积分运算的可行方法,针对积分初值及零点漂移问题,提出预估法并采用一阶惯性环节来取代积分环节进行逐步逼近,给出了电流有效值和相位的简便计算方法。仿真分析表明,该算法与传统加数据窗口的离散傅里叶计算方法相比,可有效减少短路故障条件下电流信号的处理时间,且是可行的。此计算方法同样适用于电压信号的处理过程。     

A new scheme for inrush identification in transformer protection

The second harmonic component is commonly used for blocking differential relay in power transformers. The altitudes of harmonics and fundamental are computed by discrete Fourier transform (DFT). However, this method is not effective in some cases. A new scheme to discriminate fault current and inrush current is presented in this paper. The ratio of the power spectrum (PS) of second harmonic to the PS of fundamental based on autoregressive process is used for inrush identification. Test results with the sampled data from a prototype device on a dynamic power system model verify the effectiveness of the proposed scheme.     

新型电力网络仪表的谐波测量方法与实现

研制高性能电力参数监测设备已成为市场的迫切需要。文中介绍了一种新型数字式电力监测网络仪表的设计方法。采用快速傅里叶变换(FFT)的基-2算法,通过傅里叶分解对畸变波形的各种分量进行分析,将采样取得的N个离散信号通过离散傅里叶变换得到各次谐波分量的频谱,目的是为了计算出电流电压有效值及其相应的总谐波畸变率,并且可以测量出功率、功率因数等各种电力参数,通过CAN现场总线实现对电网电能质量的远程自动监测。该方法采用数字信号处理器(DSP)在PMM 2000数字式电力监测网络仪表中得以实现,电流电压的测量精度为0.2%,其它电力参数的测量精度为0.5%。     

Slow sampling on-line harmonics/interharmonics estimation technique for smart meters

This paper presents a modified gradient search (MGS) technique to estimate harmonics/interharmonics of power system voltages and currents. The proposed technique, which is applied to spectral estimation, consumes very low processing power and needs a few samples per cycle for real-time implementation in smart meters. The computational burden of the proposed technique is lower than the discrete Fourier transform (DFT) and fast Fourier transform (FFT) and can be implemented recursively on digital signal processors (DSPs). In addition, the effects of slow sampling on the accuracy and estimation latency have been investigated. Performance of the proposed method is evaluated by simulations in MATLAB-Simulink and confirmed by experimental results.     

Correction of saturated current transformers secondary current using ANNs

Current transformers (CTs) provide instrument-level current signals to meters and protective relays. Protective relays' accuracy and performance are directly related to steady-state and transient performance of CTs. CT saturation could lead to protective relay maloperation or even prevent tripping. This paper proposes the use of an artificial neural networks scheme to correct CT secondary waveform distortions. The proposed module uses samples of current signals to achieve the inverse transfer function of CT. Simulation studies are preformed and the influence of changing different parameters is studied. Performance studies results show that the proposed algorithm is accurate and reliable. The proposed algorithm has also been implemented and tested on a digital signal processor board. Details of the implementation and experimental studies are provided in this paper.     

A Kalman filter based digital percentage differential and groundfault relay for a 3-phase power transformer

The design and real-time implementation of a Kalman-filter-based digital percentage differential and a ground-fault protection scheme for three-phase power transformers are presented. A set of eleven-state Kalman filters is used to estimate the fundamental and up to fifth harmonic components of the transformer current signals. The protective relay is equipped with an even harmonic restraint during magnetizing inrush conditions and a fifth harmonic restraint during overexcitation conditions. The restraint during external faults is provided by means of a percentage differential characteristic. The relay operates in half a cycle during internal faults. In order to achieve sensitive ground-fault protection, separate primary and secondary ground-fault protection are provided. The relay algorithm is implemented on a single TMS320 digital signal processor and tested in real time using a three-phase laboratory power transformer     

A differential relay for power transformers using intelligent tools

This paper presents alternative approaches using artificial neural networks (ANNs) for the protection of power transformers. A complete protection scheme was implemented. An ANN subroutine was used to discriminate internal faults from other situations, replacing the traditional Fourier method for harmonic restraint. In addition, a routine for reconstruction of saturated current signals based on recurrent ANNs is also proposed. The proposed methods were extensively tested and then compared to the traditional differential protection algorithm, showing promising results. The application of the ANN tools is a new and important stage in the differential relay analysis methodology for power transformer protection.     

基于矩阵束算法的电力系统非整数次谐波检测方法

针对傅里叶变换检测非整数次谐波有频谱泄露,检测精度不高等缺点,将一种子空间算法———矩阵束算法应用到非整数次谐波的检测领域,得到了较为理想的检测效果。通过MATLAB的m文件实现了矩阵束算法和傅里叶变换算法,然后分别从噪声和采样点数少对检测结果的影响两方面,对两种算法的检测精度进行了分析比较,结果表明矩阵束算法在非整数次谐波检测方面性能优越。     

快速自适应付里叶变换（AFT）及其在多维数据压缩中应用

介绍了一种新的用于多维数据压缩快速自适应付里叶变换算法 ,并将其性能与经典的算法如付里叶变换和哈达玛变换算法的性能进行了比较 ,结果证明本方法具有更高的压缩度     

A digital simulator for determining the performance limits ofcomputer relays

Unlike most other digital simulators that generate test waveforms for specific system configurations, playback previously recorded fault waveforms, or randomly generate artificial waveforms, the digital simulator presented in this paper generates the worst case waveforms for specified bounds on noise components present in the relay input signals. As a result, the performance limits of a computer relay can be determined, for specified bounds on its noise components, by performing a single test only. The parameters that define the worst case waveforms; are obtained by utilizing a modified univariate search algorithm. The PC-based simulator was implemented using a general-purpose multifunction card and a graphical programming package called Visual Designer. It did not require any text-based programming for tasks such as interfacing, digital-to-analog conversion, and outputting the discrete analog values of the generated waveform under hardware control. For demonstrating the operation of the digital simulator, a computer relay was also developed in the laboratory and its performance limits were determined     

一种用于继电保护测试装置的闭环控制正弦基准生成系统

针对目前继电保护测试装置在应用中实现小型化、智能化的需求,设计出了基于FPGA的闭环控制正弦信号基准生成系统。该系统采用FPGA作为片上系统,在芯片内集成了数字滤波器和PID控制器。设计出了低通和高通两种数字滤波器的原型,并通过递推算法在片内实现其功能。分析了解调中的幅值相位分离理论,并给出了相位环路和幅度环路的闭环控制框图,推导了控制器的离散表达式。实验结果表明,所设计的信号处理系统在输出信号幅值大于5V时,误差小于万分之一。当输出幅值信号较小时,相比开环系统,采用闭环控制系统的输出精度得到了明显的改善。在FPGA片内实现闭环正弦生成系统,为继电保护测试装置在保证精度的前提下提高系统集成度,提供了一种全新的设计思路和实现方法。     

电功率微机测量新算法

研究一种基于时域积分的电功率数字测量新算法。算法先将有功功率、无功功率的测量,转化为对瞬时有功功率和瞬时无功功率的直流分量的估计,然后基于加窗离散傅里叶变换(discrete Fourier transform, DFT)和离散傅里叶逆变换(inverse discrete Fourier transform, IDFT)实现Hilbert变换,将周期电压信号各频率分量准确移相90°,最后利用矩形自卷积窗,设计高性能FIR梳状滤波器,高效率地滤除瞬时功率信号中的基波及谐波分量。算法实现了在采样存在同步误差时有功功率和无功功率的高精度估计,仿真和科研实践验证了算法的可行性和有效性。     

An adaptive sampling-interval generator for digital relaying

A method for measuring frequency at a fixed sampling rate is described, and a variable-rate method is introduced. An algorithm based on a digital Fourier transform, which locks the sampling frequency in a microprocessor-based system to the fundamental of an incoming voltage waveform, is devised. The algorithm also intrinsically provides a measurement of the frequency. The algorithm is applied to the case of a volt/hertz relay     

A new frequency tracking and phasor estimation algorithm forgenerator protection

Digital generator protection is a complex and difficult problem. Analog and solid state methods have been successfully applied to generator protection in the past and implementation of these functions in a digital device is a continuing trend. This paper explores a new method to implement frequency tracking and phasor estimation in a numerical relay. A new algorithm is presented which utilizes a variable window discrete Fourier transform (DFT) for frequency tracking. Use of the DFT to compute the phasor estimates at a frequency other than the assumed frequency is outlined first. Next, a new technique for tracking the frequency is outlined. The paper concludes with testing of the new algorithm     

自适应突变量继电器及其傅里叶算法

以实现继电器数字算法为出发点,阐述了快速继电器动作速度与数据窗长度的矛盾。为了解决此矛盾,在实现继电器时常采用不同的算法。短数据窗算法计算速度快,长数据窗算法计算得到的数据准确度高。文中选择长数据窗的全波傅里叶算法实现继电器,保证计算过程的准确性,并简化应用在突变量继电器中的傅里叶算法。快速继电器中的比幅式过量继电器的动作方程表现为动作量大于制动量。为满足文中突变量继电器作为快速继电器的要求,根据其动作量变化特征,在制动量中引入制动系数,实时修正动作特性,以满足动作速度的要求。     

电力系统故障暂态信号分析中基波提取的新方法

电力系统故障暂态信号中基频分量的定量分析是电力系统微机保护的重要依据。已提出的基波提取算法主要有谐波分析法、暂态波形分析法。本文从谐小分析法的故障信号模型出发,给出了计算衰减直流分量的初始值和衰减率的公式,从而在滤除衰减直流分量的基础上再利用富氏算法就能得到的基频分量的精确值。在此基础上,本文又给出了精简的算法。它能在保证良好精度的基础上又满足保护快速及算法简单的要求。仿真结果证明了这些算法的有效     

基于单片机的RTU三相交流采样技术

描述一种基于80C51系列单片机实现三相交流采样的典型RTU(远程终端)的基本结构,介绍其采样信号预处理模块的原理,以MAXIUM公司模数转换芯片MAX125为核心构建一个应用电路。通过分析三相交流算法的特点,给出适合单片机实现的时域积分算法和离散傅氏变换算法的表达式,还给出基于C语言算法实现的3个重要模块。