Single-phase-to-ground fault protection based on zero-sequence current ratio coefficient for low-resistance grounding distribution network

Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs.

Zero-sequence Current Suppressing Strategy for Dual Three-phase Permanent Magnet Synchronous Machines Connected with Single Neutral Point

Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.

Zero-Sequence Current Suppression Strategy for Open-End Winding Permanent Magnet Synchronous Motor Based on Model Predictive Control

Compared with the traditional three-phase star connection winding,the open-end winding permanent magnet synchronous motor(OW-PMSM)system with a common direct current(DC)bus has a zero-sequence circuit,which makes the common-mode voltage and the back electromotive force(EMF)harmonic generated by the inverters produce the zero-sequence current in the zero-sequence circuit,and the zero-sequence current has great influence on the operation efficiency and stability of the motor control system.A zero-sequence current suppression strategy is presented based on model predictive current control for OW-PMSM.Through the mathematical model of OW-PMSM to establish the predictive model and the zero-sequence circuit model,the common-mode voltage under different voltage vector combinations is fully considered during vector selection and action time calculation.Then zero-sequence loop constraints are established,so as to suppress the zero-sequence current.In the end,the control strategy proposed in this paper is verified by simulation experiments.

计及互感器融合偏差的变电站站用电剩余电流监测系统研究

稳定的站用电源系统是变电站生产设备可靠工作之本,一旦站用电系统出现问题将直接或间接地影响变电站安全。目前变电站站用电绝缘监测主要通过对变电站电源系统剩余电流实时监测实现。然而剩余电流监测方法主要面向多电流互感器融合测量场合,现有的测量系统未考虑融合过程中互感器偏差影响,致使误报警状况频出。有鉴于此,本文提出了一套计及互感器融合偏差的变电站站用电剩余电流监测系统。该系统同步采集并实时合成多通道电流互感器剩余电流数据,并利用自回归差分移动平均模型(ARIMA)对剩余电流进行时序建模与异常检测,再使用小波阈值去噪算法对修复后的剩余电流序列降噪,以实现剩余电流的高效、精准监测。为验证所提出系统的有效性,在变电站进行现场试验。结果表明,该系统能够成功识别并修复剩余电流异常值数据且去噪效果显著。修复数据最大绝对误差仅5.9 mA,与0.5S级互感器测量数据相比,去噪后数据平均绝对百分比误差与均方根误差分别降低了0.024与1.222。

电缆终端搪铅涡流检测信号小波去噪参数选择方法

电缆终端搪铅质量直接影响高压电缆的安全稳定运行,有必要对其进行脉冲涡流无损检测,以排查是否存在缺陷。在实际检测时,涡流检测信号容易受到白噪声干扰,小波去噪是一种有效的白噪声滤除手段。然而,以往的研究通常根据经验选取小波参数,忽略了参数变化对涡流检测信号实际去噪效果的影响。因此,提出了基于粒子群优化算法的电缆终端搪铅涡流检测信号小波去噪参数选择方法,以归一化相关系数作为适应度函数,通过量化去噪涡流检测信号在峰值附近的失真程度,获得了最优小波去噪参数为Sym25小波基、10层分解层数和中位数阈值函数,保证了降噪涡流检测信号峰值大小与峰值时间的相对误差小于3%。研究成果可为确定不同噪声干扰下的涡流检测信号小波去噪参数自动选择提供方法参考。

Modeling Rogowski Coils for Monitoring Surge Arrester Discharge Currents

Rogowski coils(RCs)are widely used to measure power or high frequency currents based on their design.In this paper,two types of RCs that are circular(traditional)and cylindrical shapes wound using wire covered by varnish are constructed.This construction is carried out to be suitable for monitoring the discharge current of the surge arrester installed in the distribution system.Concerning high frequency RC modeling for both types considering transfer function is introduced.Self-integrating for both types is attained.Therefore,the experimental tests using function generator for both coils are carried out to identify the parameters of the transfer function representing the introduced model.The measured signals for current and induced voltages are denoised for the parameter identification process.The denoised process is achieved using the MATLAB code‘wdenoise’while the parameters are estimated using the system identification toolbox.Verification of the proposed model is achieved using experimental results for the two coils.The sensitivity of the two coils is investigated based on the induced output voltage.The application concerning the two coils for monitoring the discharge current of the surge arrester is done.The results confirm the accuracy of the introduced RC model,as well as the performance of the cylindrical shape,is better than the traditional one.The simulation is carried out using MATLAB and ATPDraw programs.

基于改进变分模态分解和小波阈值法的单相接地故障电流降噪

针对电力系统输配电线路发生单相接地故障时,电气设备间的电磁环境复杂,现场环境干扰严重导致故障录波装置采集到的故障零序电流信号含有大量噪声,影响后续选线准确率的问题,提出了一种改进变分模态分解(variational mode decomposition,VMD)和小波阈值法联合的单相接地故障的零序电流降噪方法,通过北方苍鹰优化算法优化改进VMD对零序电流信号分解,引入自适应相关阈值对分解后的分量进行筛选,对噪声分量进行小波阈值法降噪,最后将信号进行重构。通过搭建模型进行仿真实验,所提算法比传统VMD降噪算法信噪比提高了5.52%~35.99%,均方根误差降低了12.78%~30.88%,与小波阈值降噪方法、经验模态分解(ensemble empirical mode decomposition,EEMD)-小波阈值降噪方法、完全自适应噪声集合经验模态分解(complete ensemble empirical mode decomposition with adaptive noise,CEEMDAN)-小波阈值降噪方法相比,也都有明显的优势,并且在标准测试信号Heavy Sine信号和Bumps信号中进行实验,验证了算法的适用性。

氧化锌避雷器在线监测泄漏电流信号去噪研究

为了更有效地去除泄漏电流中的噪声成分,提高氧化锌避雷器的在线监测性能,利用改进S变换在信号时频分布处理方面的优良特征,提出一种基于改进S变换的泄漏电流二维时频去噪方法。为了更好地评估泄漏电流信号的去噪效果,还提出波峰陡度值和平均幅值两个新的评估指标。不同噪声强度下的泄漏电流去噪对比试验表明了所提出的去噪方法优越性,其研究成果能为氧化锌避雷器的泄漏电流去噪及其在线监测提供有效的参考和指导。

Pulsed Eddy Current Signal Denoising Based on Singular Value Decomposition

The noise as an undesired phenomenon often appears in the pulsed eddy current testing(PECT)signal, and it is difficult to recognize the character of the testing signal. One of the most common noises presented in the PECT signal is the Gaussian noise, since it is caused by the testing environment. A new denoising approach based on singular value decomposition(SVD) is proposed in this paper to reduce the Gaussian noise of PECT signal. The approach first discusses the relationship between signal to noise ratio(SNR) and negentropy of PECT signal. Then the Hankel matrix of PECT signal is constructed for noise reduction, and the matrix is divided into noise subspace and signal subspace by a singular valve threshold. Based on the theory of negentropy, the optimal matrix dimension and threshold are chosen to improve the performance of denoising. The denoised signal Hankel matrix is reconstructed by the singular values of signal subspace, and the denoised signal is finally extracted from this matrix. Experiment is performed to verify the feasibility of the proposed approach, and the results indicate that the proposed approach can reduce the Gaussian noise of PECT signal more effectively compared with other existing approaches.

变电站直流电源并联均流控制方法

传统方法在变电站直流电源并联均流控制中的应用效果不佳,不仅直流电源并联均流度比较低,而且均流时间比较长,无法达到预期的控制效果,为此提出变电站直流电源并联均流控制方法。利用传感器拾取直流电源信号,并采用小波降噪技术对原始信号进行滤波处理,根据电源并联原理识别直流电源并联均流误差,利用变换器对存在误差的直流电源电压进行调整,消除均流误差,从而实现变电站直流电源并联均流控制。经实验证明,在设计方法应用下,直流电源并联均流度在95%以上,均流时间为0.21 s,设计方法在变电站直流电源并联均流控制方面具有良好的应用前景。

纳米通道单分子检测低噪音电流放大器系统的研究

研制了一种新型微电流放大器系统,用于检测α-Hemolysin生物蛋白纳米通道在单分子检测实验中所产生的微弱电流信号(<100 p A)。在1 mol/L KCl、10 mmol/L Tris-HCl,1 mmol/L EDTA的缓冲液(p H 8.0)中测定了DNA-PEG-DNA交联物与纳米通道的穿越和碰撞信号。实验中使用3 k Hz贝塞尔滤波器和100 k Hz模数转换器来对电流进行采样。结果表明,此放大器系统能够有效降低电流记录过程中的噪音,有利于分辨待测物分子与纳米通道作用所产生的较小阻断的电流信号(<10 p A)。

一种触电信号的自动快速检测模型

针对未来低压电网剩余电流保护与动作技术中,如何检测触电时刻并识别总泄漏电流中人体触电支路电流信号的难题,利用数字信号的智能处理技术和具有自适应性与最佳逼近特性的组合神经网络有机结合,提出了一种触电电流信号的自动检测方法。在对低压电网中原总泄漏电流信号进行小波消噪基础上,实现了触电时刻的自动检测,触电故障模式分类归属的决策;同时从总泄漏电流中提取触电电流幅值波形。仿真实验表明:该方法速度快且稳定,模式分类正确率达100%,提取幅值与实际值的平均相对误差为3.65%,计算时间为0.064 68 s,具有良好的适应性和实用性,对于开发新一代剩余电流保护装置具有重要的参考价值。

融合超高频及脉冲电流法的局部放电监测系统

基于脉冲电流法和超高频法的基本原理和特点,研制出融合超高频法及脉冲电流法的局部放电监测系统。系统采用简易的超高频信号波形转换装置,将超高频信号转换成方波信号作为脉冲电流传感器的触发信号,避开了超高频方法需要高速采集和海量存储的缺点。与传统的脉冲电流法比较,系统有效地去除了局部放电信号中所包含的脉冲型干扰。实验结果表明该系统可以准确地识别局部放电及干扰信号,有针对性地找出干扰源并有效地去除干扰信号。

基于脉冲远场涡流的管道内检测技术

针对传统远场涡流检测方法对铁磁性管道内外壁缺陷灵敏度相同,无法有效区分缺陷在管道内壁还是管道外表面的问题,提出了采用具有丰富频率成分的脉冲激励信号取代传统的远场涡流中正弦信号激励的方法。采用小波去噪方法滤除检测数据中的信号噪声;研究了将检测线圈分别置于近场区、过渡区和远场区时的信号时域特性与管壁伤的关系;进行了针对管道管壁内外相同宽度不同深度缺陷的检测试验,结果表明采用脉冲激励作为激励源并综合运用过渡区的检测信号的幅值和过零时间特征能够有效地区分管壁内外全周向的缺陷。

煤矿高压电缆绝缘在线监测研究

分析了煤矿高压电缆出现水树枝老化、电树枝老化和整体均匀劣化下的电气特性,采用小波消噪技术和基于正交分解的信号分离技术进行接地线电流噪声处理,通过接地线电流的变化趋势和设定阈值来判断电缆是否发生绝缘劣化。Matlab仿真结果表明,研究各条线路的绝缘参数变化与相应接地线电流不同分量的关系,可实现对煤矿高压电缆绝缘在线监测特征信号的提取。

基于小波理论的电机电流信号消噪研究

小波分析是当前应用数学和工程学科中一个迅速发展的新领域。小波分析具有良好的多分辨分析能力,因而已广泛应用于信号和图像的消噪。而对电机电流信号进行消噪对于整个工程系统的分析具有很重要的意义,因此采用小波阈值消噪法对电机的电流信号进行了消噪。首先介绍了小波阈值消噪法的原理,然后用noisbump信号验证小波阈值消噪法的可行性,之后再用该方法对实验测取的电机电流信号进行消噪。消噪的效果表明:采用小波阈值消噪法对电机电流信号进行消噪,是一种可行的方法。

气流环境中纳秒脉冲沿面介质阻挡放电的特性

纳秒脉冲沿面介质阻挡放电在流动控制领域有很好的应用前景,研究纳秒脉冲沿面介质阻挡放电特性对于认识纳秒脉冲放电的物理过程具有重要意义。首先建立了沿面介质阻挡放电的电路模型,并基于小波软阈值降噪法对实验获得的纳秒脉冲电压和回路总电流波形进行降噪,然后根据对所建立的电路模型的分析给出了放电电流的计算方法,进而研究了气流环境中不同脉冲电压幅值、脉冲重复频率和脉冲极性下的放电电流、电荷传输和沉积能量特性,并进行了分析。结果表明:单个脉冲的上升沿和下降沿各存在一次放电;放电电流、最大传输电荷量和沉积能量特性存在极性效应,且正相关于施加脉冲电压幅值;最大传输电荷量和沉积能量随重复频率的增加先减小后增大,且重复频率对放电电流的峰值和宽度有影响。该研究有助于对纳秒脉冲沿面介质阻挡放电发展过程的研究,并为瞬时沉积能量的计算奠定基础。

活塞涡流信号的小波阈值降噪优化研究

涡流检测信号在产生、传输及接收过程中,会引入大量的随机噪声,为了后续信号特征提取识别处理,降噪在信号处理中是必不可少的一个环节。阐述了小波阈值降噪的基本原理,搭建了活塞喉口涡流检测实验平台。采集多组涡流检测信号,结合信噪比、均方根误差两项指标,评价降噪过程中阈值、阈值函数选取的不同对降噪效果的影响,对降噪方法进行比较优选。实验结果表明:当涡流检测信号中含有大量白噪声时,启发式阈值准则和改进指数型阈值函数能够很好的实现真实信号的提取,降噪效果最优。

异构双核构架下的脉冲涡流信号实时小波去噪

针对工业现场的脉冲涡流(PEC)信号,设计了基于异构双核OMAP3530的实时嵌入式去噪的硬件与软件系统。分析了适用于实时去噪的小波基的选择,完成了基于DB4小波基的Penalty阈值法、B-M阈值法、默认阈值法的Matlab去噪仿真实验,并给出了均方根误差(RMSE)和信噪比(SNR)。结合OMAP3530硬件平台,讨论了基于DSPLINK的异构双核构架的数据共享方法,并提出一种基于固定步长滑动窗口的实时去噪算法。通过计算机仿真与实验结果表明:该系统具有信噪比高、实时性强、数据吞吐率大的优点,满足连铸现场自动检测要求。

EMD与改进SVD联合的脉冲涡流检测信号降噪方法

针对脉冲涡流检测信号非平稳性特点和强背景噪声干扰问题,提出一种经验模态分解(EMD)与改进奇异值分解(SVD)联合的信号降噪方法。首先将信号经EMD分解成一系列的固有模态函数(IMFs),根据各固有模态函数与原信号相关系数,将固有模态函数分为信号主导分量和噪声主导分量。然后使用改进SVD降噪方法对噪声主导分量进行降噪,并与信号主导分量重构得到降噪信号。基于仿真信号和实测信号对新方法的优越性和有效性进行验证,在对实测信号采用该方法处理后,结果表明该方法能将涡流检测信号信噪比提高至30.95 dB,均方误差降低至0.0260,能有效消除强噪声的干扰,为信号特征量的准确提取奠定基础。