基于宽频等值电路的变压器局部放电电气定位研究

当变压器中发生局部放电时，脉冲电流信号会沿着绕组传播，检测绕组两端脉冲电流信号即可实现对变压器局部放电的检测。为此，建立变压器宽频等值电路模型，在可能发生局部放电的高压绕组处，于不同线饼与地之间施加局部放电脉冲，模拟高压绕组不同位置对地放电，在高压套管末屏及中性点处采集脉冲电流信号，研究不同位置局部放电脉冲电流信号在变压器绕组中的传播规律。通过计算可知，脉冲电流信号在两个不同频段能量占比的比值与脉冲电流传播的距离比呈线性关系，最大误差为9.80个线饼。该方法实现了变压器局部放电的电气定位，现场实验结果验证了该定位方法的有效性。     

局部放电信号在电力变压器绕组传播过程中的畸变

由于变压器是绕组类设备，变压器内部的局部放电信号将经绕组向两端传播至监测装置，从而导致作为故障诊断基础信息的放电脉冲信号发生一定程度的畸变，该文根据对脉冲信号在绕组中传播过程的实际测量结果，获得了绕组的基本冲击响应特性，利用典型模型放电的纳秒级快速变化波形测量结果，研究了不同情况（不同放电类型、不同放电部位以及不同的测量点）下放电脉冲信号在绕组中的传播规律，并提出了一种从实际测量波形中有效分析原始放电波形的方法，为实际的局部放电脉冲波形监测提供了试验依据。     

油纸绝缘中局部放电的典型波形及其频谱特性

根据对变压器油纸绝缘内部常见缺陷的分析，进行了局部放电模型试验。通过考察不同类型放电的发展过程和电流脉冲的波形特征，发现油纸绝缘中产生的局部放电与空气中的放电过程表现出相似的发展规律。对应于不同的放电阶段，放电波形有较大差异，因而不同类型的放电脉冲具有不同的频谱特性。所得结果为深入研究绝缘介质中的局部放电的机理、放电脉冲在变压器绕组中的传播规律、局放检测系统的频率特性以及放电类型的波形识别提供了实验依据。     

变压器绕组的局部放电定位研究

通过ATP-Draw建立了变压器单绕组模型,模拟了局部放电脉冲在绕组中的传播过程,并介绍了基于分段绕组传递函数的局部放电定位方法.     

外联网络对大型变压器中局放信号传播影响的仿真分析

大型电力变压器内部的局部放电信号经绕组向两端传播至监测装置,从而导致作为故障诊断基础信息的放电脉冲信号发生一定程度的衰减、振荡及时延。运用Saber仿真软件,利用典型的局部放电的波形,考虑电力变压器外联网络复杂程度以及变电站另一个变压器对其的影响,研究了局部放电信号在大型电力变压器在线监测系统中的传播特性。     

基于多导体传输线模型的单相变压器绕组中放电的距离函数法定位

基于多导体传输线理论建立放电脉冲信号在大型单相变压器绕组中的传输模型.结合真实变压器绕组的具体结构,在频域仿真计算了绕组不同位置注入放电脉冲电流时其首末端的电流传输函数比曲线.根据绕组电流传输函数比曲线的可分性,采用距离函数法实现了变压器绕组中局部放电的电气定位.该方法根据实测与仿真传输函数之间的距离函数大小判断放电位置,180匝连续式单绕组和400kV单相变压器的模拟定位试验验证了该方法的有效性.     

变压器局部放电电气定位的分析

在对变压器局部放电的检测中，把从放电点到外部测量端的路径作为一个系统，放电发生的位置不同会使系统的传递函数存在差异，本文采用建立仿真模型并结合试验的方法，研究了不同的局部放电脉冲传播路径的传递函数，在分析传递函数频谱特性的基础上，提出了根据响应信号高频分量和能量的局部放电电气定位方法。     

变压器线圈局部放电传输模型与定位方法

建立局部放电脉冲信号在变压器线圈中的传输模型,模拟局部放电信号在线圈中的传输过程.根据变压器线圈模型等值电路,研究不同位置输入的局部放电信号与其它节点输出响应信号之间的关系,提出基于传输函数的局部放电定位方法.     

基于宽频等值电路的配电变压器局部放电电气定位研究

当配电变压器中发生局部放电时,脉冲电流信号会沿着绕组传播,检测低压绕组中性点接地处脉冲电流即可实现配电变压器局部放电检测。以往的配电变压器局部放电检测及评价方法无法判断放电位置与放电类型,难以准确评估配电变压器绝缘状态。建立了配电变压器宽频等值电路模型,研究了不同位置、不同类型局部放电脉冲电流信号在配电变压器绕组中的传播规律,提出了小波-经验模态联合去噪算法过滤现场检测中的噪声信号。通过计算脉冲电流信号的能量值以及三相波形相似系数实现了配电变压器局部放电的电气定位,以对多组不同噪声水平的信号进行验证,均可实现准确定位,验证了去噪算法和定位方法的有效性。     

数字技术用于电力变压器局部放电定位

文中作者介绍了一种电力变压器局部放电的电气定位技术。它利用在特定的频率段变压器内的放电脉冲线性传播的特点，确定局部放电位置。所创立的技术及相应的设备已在变压器出厂试验及变电站运行变压器在线监测中证明该项技术可以准确检测出故障变压器的放电位置。     

Partial discharge localization in transformer windings using multi-conductor transmission line model

Multi-conductor transmission line model (MTLM) of transformer winding has been used to find partial discharge (PD) location in transformers. To decrease computational complexity of the model, two methods for calculation of model parameters were studied and the most suitable method was chosen based on comparison between measured and calculated transfer functions of a 132 kV/20 kV transformer. To investigate the accuracy of MTLM in PD localization, PD pulses produced by a PD calibrator were injected into different points of a research 20 kV/0.4 kV transformer and measured at both ends of the winding. The sectional winding transfer functions computed by the model were used to refer measured PD signals to possible PD locations. Then by comparison of referred signals, PD location in the winding was estimated.     

能量比值法定位变压器局部放电

提出了先确定变压器两测量端信号能量比值与放电位置的关系曲线,用放电后测算得的信号能量比值确定放电位置的方法。仿真和试验表明,<1 MHZ放电信号的能量比值具有良好的位置特性,其定位特征量的误差<10%。     

基于多导体传输线模型的变压器绕组分布参数计算

为了研究局部放电信号在变压器绕组内部的传播过程,建立了变压器线圈绕组的多导体传输线模型。以40匝单层绕组为特例,根据绕组的轴对称性,建立二维等效有限元模型。考虑绕组核心材料为空心、铝心和铁心的情况,分别采用静电场和时谐磁场模型计算变压器绕组的电容、电感、电阻分布参数。对于频变参数,选取多个频率点进行时谐场计算。在求解过程中,重点考虑了趋肤效应的影响。参数计算的结果同实测的结果基本吻合,计算方法对于研究局部放电(PD)脉冲在电力设备中的传播特性有十分重要的意义。     

A measurements-based discharge location algorithm for plain disc winding power transformers

A measurements-based electrical method for locating partial discharges (PD) in transformers is described in the paper. This location method relies on the series resonance frequencies of the signals produced at the transformer terminals by a discharge on the winding. Based on the equivalent circuit of plain disc type winding which consists of series inductance (L), series capacitance (K) and shunt capacitance to earth (C) of the winding, an analytical location algorithm is derived which gives the relationship between the location of a discharge and its terminal response's series resonance frequencies. LKC parameters of the equivalent circuit can be estimated using the series resonance frequencies of a calibration signal measured at the bushing tap during PD calibration. The PD location algorithm was tested on 11 kV transformer winding using signals produced by a discharge simulator and real discharges, and the results confirm its validity with a location accuracy of better than 10% of the winding length. However, blind area where this location algorithm is not applicable does exist near the neutral of the winding and far away from the measuring terminal. Since this location algorithm uses the series resonance frequencies below 500 kHz, it can be implemented with conventional PD measuring circuitry and instruments to detect and locate discharges in power transformers.     

Using correlation coefficients for locating partial discharge in power transformer

Most serious failure of power transformers is due to the insulation breakdown. Partial discharge (PD) that damages insulation by gradual erosion is major source of insulation failure. The effective ability of the wavelet packets analysis as a tool for disk-to-disk partial discharge faults detection and localization in transformer windings is shown in this paper. Techniques for locating a PD source are of the major importance in both the maintenance and repair of a transformer. One of the most well-known methods of PD localization in transformers is based on winding modeling and current of neutral point analysis. Since the impedance between PD location and neutral point of winding depends on the PD location in respect to neutral point, the frequency spectrum of neutral point current varies when the PD location changes. In the other word, the current components of neutral points vary according to the place where PD occurs. So in this paper, detailed model of transformer winding is modeled and the neutral point current is studied for locating PD. The used method is validated by the simulated model of transformer windings. This model produces a very acceptable current when compared to the experimental data. In this paper for locating partial discharge (PD) in transformer windings, a simulated model is developed for the transformer winding and the PD phenomenon mechanism. The impulse current test and wavelet packets transformation are used to locate PD. It is shown that the neutral current measurement of the transformer winding has useful information about PD location.     

Application of wavelet analysis to the determination of partial discharge location in multiple-α transformer windings

The inner insulation system is a critical component of a power transformer. Its degradation may cause the device to fail while in service. If deterioration of the insulation system caused by Partial Discharge (PD) activity can be detected at an early stage, preventive maintenance measures can be taken. Due to the complex structure of power transformers, accurate locating of PD is not an easy task and is one of the main challenges in front of power utilities. Locating PD is more difficult in transformers with multiple-α windings. This problem comes to be vital in open access systems. A method for locating partial discharge within multiple-α windings is proposed, which is based on structural data of a transformer. A 66 kV/25 MVA transformer with fully interleaved winding and connected tap winding is used as test object. Wavelet transform is employed to process the partial discharge signals. Wavelet transform analysis method is a powerful tool for processing transients and non-stationary or time varying signals. Since the wavelet transform provides multi-scale analysis and time–frequency domain localization, it is particularly suitable to process the partial discharge signals. In order to improve the accuracy of the partial discharge location, a new technique for extracting Partial Discharge signals is introduced. Applying wavelet transform to a signal produces a wavelet detail coefficient distribution throughout the time-scale, which depends on the mother wavelet chosen. This technique is based on the capability of the chosen mother wavelet for generating coefficients with maximum values. The wavelet based de-noising method proposed in this paper can be successfully employed to extract PD pulse from the measured signal. It can provide enhanced information and further infer the original site of the PD pulse through capacitive ratio method. The method is described in details and the applications to determine the partial discharge location in multiple-α windings are explored.     

Simulation of transformer PD pulse propagation and monitoring for a500 kV substation

This paper discusses the development of a simulation model to study the propagation of partial discharge (PD) pulses of transformers in a 500 kV substation. The results will be used to design an on-line PD monitoring system for transformers. The impedance matrix of a 500 kV, single-phase transformer is computed based on geometry data and its external coupling network (often referred to as coupling impedance) is calculated with electromagnetic transients program (EMTP). It was found that the frequency characteristic of the coupling network is complex and that the traditional lumped coupling capacitance representation is only feasible at <60 kHz. The entire substation network was included to calculate the PD propagation of the transformer. PD responses are obtained at the tank grounding and 500 kV bushing tap grounding with a simulated PD pulse injected at the 500 kV terminal and 220 kV terminal of the transformer, respectively. Simulation shows that, using the resonant frequency of the substation network as monitoring frequency, one effectively can increase the monitoring sensitivity. The off-line and on-line PD calibration can also be made based on the developed simulation model