Nonlinear dynamical response of high-voltage transmission lines based on cable dropping

In order to study the dynamic response of high-voltage transmission lines under mechanical failure, a finite element model of a domestic 500-kV high-voltage transmission line system is established. The initial equilibrium condition of the coupling system model is verified by nonlinear static analysis. The transient dynamic analysis method is proposed to analyze the variation law of dynamic response under cable or insulator rupture, and the dynamic response of structural elements next to the broken span is calculated. The results show that upper crossarm cable rupture has no effect on cable tension at adjacent suspension points, but it has a significant influence on tension in the insulator and the tower component of the upper crossarm next to the broken span. The peak tension in the conductor of the upper crossarm at the suspension point exceeds the design value under insulator rupture. Insulator rupture has no effect on the tower component of the upper crossarm, but it has a significant influence on insulator tension of the upper crossarm. Insulator rupture should be taken into account in the design of overhead transmission lines. The research results can provide a theoretical basis for the design of transmission lines.

TRANSIENT ANALYSIS OF NONUNIFORM TRANSMISSION LINES WITH NONLINEAR TERMINAL NETWORKS

A semi-analytical method in time domain is presented for analysis of the transient response of nonuniform transmission lines. In this method, the telegraph equations in time domain is differenced in space domain first, and is transformed into a set of first-order differential equations of voltage and current with respect to time. By integrating these differential equations with respect to time, and precise computation, the solution of these differential equations can be obtained. This method can solve the transient response of various kinds of transmission lines with arbitrary terminal networks. Particularly, it can analyze the nonuniform lines with initial conditions, for which there is no existing effective method to analyze the time response so far. The results obtained with this method are stable and accurate. Two examples are given to illustrate the application of this method.

Dynamic response of cylindrical lined cavity in elastic medium

An analytical solution to the transient dynamic response of a cylindrical lining subjected to an internal loading was presented and the dynamic interaction between the lining and surrounding soil was considered. The lining structure and the soil were treated as a cylindrical elastic shell and an infinite elastic compressible medium, respectively. A two-dimensional axisymmetric wave equation was derived from the governing equation of displacement by introducing the potential functions. Shell equation of motion was established based on continuity conditions. The closed-form solution for dynamic response of the lining due to an impact loading was obtained in Laplace transforms and inverse transforms. Detailed parametric studies were also presented to illustrate the influences of the Poisson ratio of soil, the dynamic shear moduli of both soil and lining and the thickness of lining on dynamic response of the lining.

Mitigation of Transients in Capacitor Coupled Substations Using Traditional RLC Filter Techniques

This article presents an extensive examination and modeling of Capacitor Coupled Substations (CCS), noting some of their inherent constraints. The underlying implementation of a CCS is to supply electricity directly from high-voltage (HV) transmission lines to low-voltage (LV) consumers through coupling capacitors and is said to be cost-effective as compared to conventional distribution networks. However, the functionality of such substations is susceptible to various transient phenomena, including ferroresonance and overvoltage occurrences. To address these challenges, the study uses simulations to evaluate the effectiveness of conventional resistor-inductor-capacitor (RLC) filter in mitigating hazardous overvoltage resulting from transients. The proposed methodology entails using standard RLC filter to suppress transients and its associated overvoltage risks. Through a series of MATLAB/Simulink simulations, the research emphasizes the practical effectiveness of this technique. The study examines the impact of transients under varied operational scenarios, including no-load switching conditions, temporary short-circuits, and load on/off events. The primary aim of the article is to assess the viability of using an established technology to manage system instabilities upon the energization of a CCS under no-load circumstances or in case of a short-circuit fault occurring on the primary side of the CCS distribution transformer. The findings underscore the effectiveness of conventional RLC filters in suppressing transients induced by the CCS no-load switching.

隧道内爆炸荷载作用下衬砌及周围非饱和土的动力响应解答

假设瞬态荷载沿隧道方向按指数衰减,建立非饱和介质中圆柱形衬砌隧道受到内源爆炸荷载作用时衬砌隧道及周围非饱和介质计算模型。基于多孔介质混合物理论和连续介质力学理论,推导爆炸荷载作用下衬砌结构及周围非饱和土的控制方程,运用Laplace及Fourier变换求得隧道衬砌及周围土体在频域-波域内的解析解答,研究内源爆炸作用下饱和度对衬砌结构动力响应的影响。计算结果表明:饱和度对衬砌内表面径向位移影响较大,在轴向上,随着饱和度由0.15增至0.98,爆源处的径向位移值升高约28%;衬砌内表面径向应力随时间变化受饱和度的影响不明显;衬砌内表面环向应力幅值随饱和度的增大而增大,且达到幅值所用的时间逐渐延迟。在轴向上,随着饱和度由0.15增至0.98,爆源处环向应力升高约29%。

一种基于CNN与FFT‑ELM的输电线路故障识别与定位方法

及时、准确地检测输电线路故障类型与位置是提高电力系统可靠性最重要的问题之一,为此提出一种基于卷积神经网络(convolutional neural networks,CNN)与基于快速傅里叶变换(fast Fourier transform,FFT)的极限学习机(extreme learning machine,ELM)分类模型并行的输电线路故障识别及定位方法。首先,以故障电压时序图作为输入,构建CNN;然后,利用FFT将时域故障电压数据分解,提取各频段的电压峰值与相角作为故障特征样本;接着,以提取的故障特征样本集作为输入,构建ELM网络;最后,通过特征融合层将2个神经网络进行融合,输出故障类型和定位结果。实验结果表明,此方法对输电线路故障识别的准确率为99.95%、故障定位误差在500 m以内、平均误差为263.5 m,可靠性优于其他模型。

基于矩阵束方法的传输线系统瞬态响应分析

带有频变负载的传输线系统的瞬态响应分析是电磁兼容领域的一个重要内容,特别是对于频变负载网络较为复杂或内部结构不清晰的情况,其瞬态响应的分析较为困难。本文首先在采样频率点处对频变负载端口导纳进行测量或计算得到相应的采样导纳,并采用有理函数逼近的方式对端口导纳进行等效;之后采用矩阵束(MPM)方法求解出有理逼近函数所需的极点和留数,并将其代入到分段线性递归卷积(PLRC)技术中,实现传输线和频变负载连接点处电压的分段线性递归卷积表达;最后,结合传输线方程实现带有频变负载的传输线系统的瞬态响应分析,并通过2个算例对所提方法的性能进行验证。结果表明,所提方法在计算精确度上具有明显的优势。

Analysis of transient viscoelastic response of asphalt concrete using frequency domain approach

The analysis of transient linear viscoelastic response of asphalt concrete （AC） is important for engineering applications. The traditional transient response of AC is analyzed in the time domain by performing complicated convolution integral. The frequency domain approach allows one to determine the transient responses by performing simple multi- plication instead of the complicated convolution integral, and it does not require the time derivative of the input excitation, and thus, the approach could greatly reduce the analysis complexity. This study investigated the frequency domain approach in calculating the transient response by utilizing the discrete Fourier transform technique. The accuracy and effectiveness of the frequency domain approach were verified by comparing the analytical and calculated responses for the standard 3-parameter Maxwell model and by comparing the time and frequency domain solutions for AC. The effect of aliasing of the frequency domain approach can effectively reduce by selecting a small sampling interval for the time domain excitation function. A sampling interval is acceptable as long as the amplitude of the Fourier transformed excitation is close to 0 more than half of the sampling rate. The results show that the frequency domain approach provides a simple and accurate way to perform linear viscoelastic analysis of AC.

现代行波故障测距系统的研制

介绍了一种采用现代行波故障测距技术的架空输电线路故障测距系统的构成、工作原理、功能配置及其在交直流输电系统中的应用实例。该系统由行波采集与处理系统、行波综合分析系统、远程维护系统以及公共电话网等 4部分构成 ,并且集成了 A,D,E等 3种现代行波故障测距原理以及多种暂态行波波形分析方法。该系统可以同时采集 8回线路的暂态电流 (来自常规电流互感器二次侧 )和暂态电压 (来自专门研制的行波耦合器 )信号。实际运行表明 ,该系统具有较高的准确性、可靠性、性能价格比以及较强的适应性和可维护性 ,其绝对测距误差可达 2 0 0

特快速暂态过电压下变压器绕组高频电路模型的研究

变压器绕组的高频模型对于分析特快速暂态过电压对变压器的影响是非常重要的。从易于高频测量的散射参数出发,提出了一种建立变压器绕组高频电路模型的方法。该方法首先由散射参数计算绕组各匝的电压传输函数,并利用矢量匹配法对得到的电压传输函数进行有理函数逼近;其次,对得到的有理函数形式的传输函数进行阶数缩减,得到变压器绕组电压传输函数的降阶模型;最后,运用网络综合技术建立变压器绕组的高频电路模型。该电路模型简单、通用,仅由R、L、C和理想变压器构成,其模型参数可以根据电压传输函数的极点和留数非常方便地得出。通过对电路模型的仿真结果与实际测量结果进行比较,验证了文中方法的正确性。

BLT方程的时域扩展及其在微带线中的应用

以微带线为应用背景,使用拉普拉斯逆变换将频域BLT方程中的乘积运算转换为时域卷积,结合级数运算,将频域BLT方程扩展到时域BLT方程,并应用该时域BLT方程计算了均匀有耗微带线的瞬态终端响应电压。数值仿真结果表明,时域BLT方程与频域BLT方程的计算结果一致,从而验证了扩展得到的时域BLT方程的有效性,仿真结果也为微带线的集总源激励效应研究提供了参考。

利用暂态电流行波的输电线路故障测距研究

高压输电线路发生故障后的暂态电流行波中包含故障距离信息，它可用于实现精确故障测距。利用电流行波实现测距存在的问题是：电流行波无方向性，可能造成测距失败。针对这个问题，提出了基于小波变换模极大值的波形比较法。同时提出了行波测距的新算法——小波变换法。ＥＭＴＰ仿真结果表明：文中所提理论和方法对于实现利用电流行波的故障测距是正确的和有效的。

不同能量光子辐照电缆响应规律研究

利用时域传输线(TL)方法计算了不同能量光子辐照同轴屏蔽电缆时的响应规律。计算结果表明:光子能量不同时,电缆介质层中沉积电荷分布不同导致电缆响应极性发生了变化;光子能量增大到一定值后,响应变化幅度很小;1MeV的单能电子经钽靶发生韧致辐射后在电缆上的瞬态辐照响应是前向电子和光子在电缆上响应的综合,两者在电缆上的电压响应均为负值,幅度差别在1.8倍以内;钽靶后面增加一定厚度的铝材料,可明显减小前向电子在电缆响应中的比例。

用ATP-EMTP研究1000kV CVT的暂态特性

为研究1000kV电容式电压互感器(CVT)的暂态特性,在分析其非线性元件的饱和特性后,利用电磁暂态计算程序ATP-EMTP建立了1000kV CVT计算模型。对不同阻尼电阻值下的铁磁谐振进行仿真,得出了理想的阻尼电阻值,计算结果与实际采用阻尼电阻值相吻合;在不同合闸相角下分别对CVT铁磁谐振以及瞬变响应进行仿真计算,铁磁谐振过电压波形的仿真结果与试验结果基本一致,得出最严重情况下的谐振过电压倍数和二次瞬变响应电压值。研究结果不仅可以实现1000kV CVT设计阶段的暂态性能参数控制,同时解决了试验无法模拟现场实际条件的矛盾,为晋东南-南阳-荆门1000kV特高压交流试验示范工程中CVT暂态特性提供考核手段之一。

VFTO作用下变压器绕组的过电压计算

为研究气体绝缘变电站中陡波前过电压对变压器的影响和解决大型电力变压器建模时矩阵阶数过大问题,详细推导了以匝为单元建立的变压器绕组多导体传输线(MTL)模型的计算公式,提出了该模型结合等效阻抗建立变压器绕组模型的新方法,有效地提高了计算效率。仿真与试验结果说明该法正确可行。

超高压输电线路新单端暂态量保护元件的实用算法

在线路边界频率特性的分析基础上,深入地分析了区内外故障时的特征差异:就某一类故障而言,区外故障时反行波中(阻塞频带内的)高频分量与(1-10kHz内的)低频分量的比值显著小于区内故障时的比值。据此提出利用反行波构造新型的单端暂态量保护原理,即反行波法边界元件,并形成基于小波变换的实用算法。大量ATP仿真表明,该边界元件的算法可行,动作超高速,且性能优于利用电流波的单端暂态量保护方案。文中还指出:对于实际的输电系统,现有的单端暂态量保护方案都难以保护线路全长,因此该方法可以作为全线速动保护的一种超高速保护元件。

用于绝缘油中气体监测的半导体气敏传感器模型

利用塔板理论建立混合气体色谱柱分离的数学模型;分析了半导体气敏传感器的稳态、暂态响应与恢复特性,提出了关于传感器响应与恢复特性的3个假设:传感器稳态输出电阻的对数与气体浓度的对数服从正切关系,暂态响应特性取决于传感器当前的阻值状态和当前时刻的气体浓度, 恢复特性取决于传感器当前阻值状态和下一时刻的气体浓度。采用实验与数值逼近等数学方法确定所需参数。最后设计了验证实验,结果表明将3个假设用于油中气体监测系统的半导体传感器能够满足要求。

基于小波变换的行波故障选相研究第2部分仿真试验结果

构造了一个新型行波故障选相元件，其基本原理是计算模量初始电流行波在小波变换下的模极大值，根据３个模量的故障特征选择故障相。该选相元件克服了传统选相元件的缺陷，充分利用了电流行波中的模故障分量特征，从而使选相结果准确、可靠、ＥＭＴＰ仿真结果证明了该选相元件的有效性和正确性。

建筑物雷电保护系统内部最大磁场强度的计算

雷击建筑物引起的电磁干扰和电磁兼容问题是建筑物雷电防护的重要研究课题。为此,研究了雷击建筑物时防雷系统暂态电流分布以及内部磁场分布的计算。采用传输线模型对防雷系统进行等效,采用时频变换技术对该模型进行求解,并根据电流分布的计算结果采用解析方法对建筑物内部磁场分布情况进行了求解。然后根据计算结果,从参数变化的角度对IEC标准给出的磁场近似计算公式的合理性和适用性进行了分析和验证。结果表明,IEC标准中的近似公式所忽略的"空间位置"和"接地电阻"两个因素对建筑物雷电保护系统内部最大磁场强度的计算精确度影响较大,而其他因素的影响较小。

输电线路导线微风振动在线监测技术

为有效避免由输电线路导线微风振动引起的导线断股事故,设计了一套微风振动在线监测系统来实时监测导线的微风振动信息。系统采用悬臂梁式传感器测量导线的弯曲幅度,并根据弯曲幅度,采用峰峰值法和快速Fourier变换(FFT)等方法,计算出导线振动的频率与振幅以及导线的动弯应变。研究表明,悬臂梁式传感器可以准确测量频率1～150Hz的小幅振动信号,峰峰值法可以准确计算出导线微风振动的振幅,而快速Fourier变换可以准确计算出导线振动的频率。根据研究结果可知,该系统采用的测量方法和建立的数学模型可以准确计算出导线的动弯应变值,并能实现输电线路疲劳故障的预警。