晶闸管控制串联电容换级特性研究

研究了晶闸管控制的分级串联电容换级时的暂态过程。采用编程仿真的方式,对单级电路和多级电路分析后,提出了晶闸管开关最佳接入时刻为被短接电容电压为零时;分析了阻尼电阻、电感对暂态过程的影响以及它们之间的参数配合;采用电容分级式可控串补策略可大大降低可调电感容量及成本。高压输电线路分级电容可控串补的应用可提高系统的稳定性。     

Calculation of frequency response of thyristor‐controlled series capacitor

In this paper, we propose a method of analytically calculating an impedance of a thyristor‐controlled series capacitor (TCSC). The TCSC consists of a thyristor‐controlled reactor (TCR) and a capacitor. If a small voltage component of frequency f superimposes the TCSC voltage of frequency f_o, then current components of frequency (nf_o ± f) flow through the TCR, where n takes even numbers. We derive theoretical equations for them. In the derivation, we consider an influence of odd harmonics in the TCSC voltage. We also consider deviations in its zero‐crossing times due to the superimposed voltage. The current components flow through the capacitor and the transmission line, and produce new voltage components of frequency (nf_o ± f). In order to count their influence, we introduce admittance matrices for the TCR, the capacitor, and the transmission line. By solving a network equation consisting of the matrices, we can obtain the distribution of the voltage and current components. We define the impedance of TCSC as a ratio of the voltage component of frequency f to the current one of the same frequency. The impedance analytically obtained corresponds well with that obtained by simulations. Its frequency responses vary with the firing method of thyristors. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 35–44, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1158     

晶闸管控制三相电容器投切过程分析及仿真研究

针对三相供电系统中晶闸管投切电容器（TSC）的无功补偿问题,重点分析了TSC工作原理和投切过程,借助Matlab/Simulink平台对电容器的三角形外接法进行建模、动态仿真分析和研究,提出了无功补偿电容器合理投切方式和投切时刻控制方案,有效减小了投切过程中的冲击电流。     

时域和频域相结合的次同步振荡分析方法

电力系统中的次同步振荡是一类严重的系统稳定性问题,不但会使系统产生振荡现象,而且极易造成汽轮发电机组的大轴损毁。以往提出的基于系统线性化方程的小扰动分析方法不能考虑直流系统的非线性因素,而且在实际复杂系统中的应用非常困难。为解决上述问题,对复杂交、直流系统的次同步振荡特性做出准确和全面的分析,对以往提出的暂态力矩时域仿真计算方法及复转矩系数仿真求解方法进行拓展。以2008年贵州电网为例,采用时域与频域相结合的分析方法对这一复杂交直流混合输电系统的次同步振荡特性进行研究,确定该系统可能发生次同步振荡的运行方式。现在的电力系统结构日趋复杂,所提供的分析方法为今后复杂交、直流输电及含有FACTS(灵活交流输电系统)装置的输电系统的次同步振荡特性分析提供了参考。     

基于时、频域自相似性的配电变压器环境噪声识别方法

配电变压器位于开放的嘈杂环境中,环境噪声对基于声音的设备运行状态在线监测具有突出影响.如何识别和剔除含噪声干扰的录音片段,是推进基于声音的配电变压器状态在线监测亟待解决的瓶颈问题.分析指出配电设备正常和异常的运行声音与各种环境噪声在时域和频域上的差异性特征,提出基于时、频域自相似性的配电设备录音数据中含环境噪声片段的识...     

Calculation of HVDC-converter harmonics in frequency domain withregard to asymmetries and comparison with time domain simulations

In order to study the effects of large HVDC power converters on the feeding AC networks, it is of importance to explain and to calculate harmonic phenomena which are a result of power converter operation. During commissioning of real HVDC power converters, it could be seen that harmonics resulting from asymmetry in the system voltages or from asymmetry in power converter operation led to significant difficulties concerning the system design. For this reason, not only the effects of characteristics but also the effects of noncharacteristic converter harmonics must be taken into account. The aim is to describe the steady state harmonic behavior of the converter. The harmonic spectra are not determined by time domain analysis but instead the solution is found by frequency domain calculations. This can result in reduced calculation time in comparison to conventional Fourier analysis of the time functions. The power converter is interpreted as an amplitude modulator with voltage and current converter functions which describe the coupling of the DC circuit and the AC network through the power converter. To verify the theory, comparisons of frequency domain with time domain calculations were carried out     

一种等效微分环节反馈滤波电容电压实现有源阻尼的方法

常规的微分实现方法在直接用于反馈滤波电容电压实现有源阻尼时易放大高频噪声,影响进网电流质量以及阻尼效果。为此,提出采用负带通滤波器串联滞后校正环节来实现等效微分环节。该方法在用于反馈滤波电容电压实现有源阻尼时,不仅能够有效地抑制LCL滤波器的谐振尖峰,还对高频噪声具有抑制作用。所提策略解决了常规微分实现方法反馈LCL滤波器状态量实现有源阻尼放大高频噪声的问题。通过搭建一台实验样机,验证了所提策略的有效性。     

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.     

Applications of dielectric spectroscopy in time and frequency domain for HV power equipment

Dielectric spectroscopy in the time or frequency domain offers new opportunities for an off-line, on-site insulation condition assessment of HV electric power equipment and its predictive maintenance.     

换流阀阻尼电容器等效温升试验及寿命评估

阻尼电容器是换流阀内核心元件,有效评估其运行寿命,对换流阀状态评估及阻尼电容器国产化研究具有重要意义。首先,文中结合换流阀阻尼电容器应用原理,提出多频率点等效温升试验方法,通过等效计算阻尼电容器实际工作时的损耗、灵活选择试验时的频率和电流,准确评估阻尼电容器实际运行时内部温度及热阻。然后,综合考虑换流阀阻尼电容器实际运行环境及工作温度,分析寿命影响因子,并在经典寿命预测模型基础上,提出老化试验与曲线拟合相结合的改进寿命预测方法,该方法能够缩短试验时长、节约试验成本。最后,结合实际工程参数分析电容器运行时的内部温升及热阻,进一步在寿命预测试验中评估试品阻尼电容器的预期寿命,所得结果满足特高压直流工程要求。     

Study of abnormal transient current of PMN-32%PT ferroelectric single crystal in time domain and frequency domain

A special test circuit was designed to measure the transient current in time domain. The measurement was performed on 0.68Pb(Mg_1/3Nb_2/3)O₃–0.32PbTiO₃ (PMN-32%PT) single crystal. Abnormal transient current was observed in time domain. Two oscillations were observed in transient current. By means of discrete Fourier transform (DFT), two peaks were found in frequency domain, which were corresponded to the resonance frequencies measured by frequency domain method. This phenomenon can be attributed to piezoelectric resonance. The transient current was calculated and fitted well based on a piezoelectric resonance equivalent electrical circuit model. Experimental results confirmed that no oscillation can be observed in PMN-32%PT single crystal samples after thermal annealing, which also verified that the piezoelectric resonance was the origin of the abnormal transient current.     

基于时频域介电响应混合的绝缘诊断装置

油纸绝缘电力设备绝缘状态的诊断与评估对于电力系统的安全稳定运行具有重要的意义。频域介电谱法具有包含绝缘信息丰富、抗干扰能力强等优点,但其低频段测试过程需要耗费大量时间,为现场测试与诊断评估带来困难。为了解决这一问题,本文采用时域法和频域法混合求解方式,在低频段,运用傅里叶变换将时域极化电流信号变换到频域,从而得到低频段的损耗因数。本文设计了一套基于时频域介电响应混合的绝缘诊断装置,其中线性级联放大器具有高带宽、高电压、低谐波畸变率的优点;微电流测量电路采用对称差分结构,有效抑制温度和工频干扰的影响。最后,通过对变压器油纸绝缘套管模型以及交联聚乙烯（XLPE）切片进行实验测试,验证了该装置测量的准确性。     

高精度无间隙时频测量技术的研究

高精度无间隙时频测量技术是时频测量领域关键技术基础。本文概述了频率比对装置所采用的频差倍增和相位比较2种技术及其原理和技术实现。提出了高精度无间隙时频测量的新方法,用计数器由同一时基控制,2个计数器交替计数采样,一个计数器关门计数,另一个计数器开门计数,这样相邻2次计数之间没有时间间隔,把N个计数周期所采样的数据累加起来,实现了无间隙采样。将采样值累积,实现原子频标、高稳晶振长时间频率稳定度和频率漂移率的测量。采用高精度无间隙连续测量技术所研制的频标比对装置,不仅可以完成一般的频率信号的时域参数的测试,而且可以替代传统的比相仪。实践表明,新的方法与传统方法相比在测试精度和测试能力上有明显提高,不仅是频率信号时域参数长期特性和短期特性为一体的综合测量装置,也是时频测量和科研开发的理想工具,值得研究和分析。     

TSC型无功静止补偿装置非同期投切对继电保护的影响分析

探讨了晶闸管开关投切电容器（ＴＳＣ） 型的无功静止补偿装置因晶闸管开关过零平滑投切而产生的不平衡现象,定量分析了在特定条件下不平衡量的大小,同时研究了这种不平衡对继电保护装置的影响。     

基于频域辨识的合并单元额定延时测量技术

智能变电站中合并单元数据采集和输出过程存在着固有的额定延时,此延时直接影响继电保护的动作时间。目前,额定延时测量方法存在着不足,给系统安全运行埋下了安全隐患。文中从合并单元采样环节的构成出发,分析其采样、处理过程中额定延时的群延迟特性和传变延迟。研究表明:时域中的群延迟在频域中相频特性应为线性相位,据此提出通过输入不同频率的信号以获得合并单元的相频特性曲线、进而辨识出额定延时的频域识别测量技术,并分析合并单元的相位误差对此额定延时测量方法的影响,最后通过理论仿真验证了此额定延时测量技术的可行性和正确性。文中所提方法为合并单元数字化采样延时测量的工程应用提供了一种切实可行的延时测量技术,能够确保继电保护系统的正确、可靠运行。     

基于训练序列的载波频率同步算法的FPGA实现

根据电力线信道的特点,采用基于OFDM技术的多载波系统来实现电力线系统载波通信,提出了一种具有实用价值的小数频率同步的实现方法。文章具体分析了基于OFDM技术的电力线通信系统的同步原理和实现方法,整个频率同步模块被分成估计和纠正2个部分。系统采用X ilinx ISE 6.2 i来完成开发,同时,给出了其在ModelSim Se5.7g下的仿真结果,通过在实际系统中的测试,证明了该同步方法是完全可行的。     

长线频域测试法研究

本文根据长线传输理论,提出了一种通过长线端口的频率特性来推算其工作状态和各种参量的频域测试法。与传统长线的空域测试法相比,它具有不破坏长线的原工作状态、自动化程度高、测量迅速的特点;其误差可以分析和控制。特别是“频域测试法”可以直接观察传输线的工作状态与负载随频率变化的特性,在高频电信号传输和辐射工程中有很大实用价值。文中给出了长线“频域测试法”的理论分析和测试实例。     

受潮对油纸电容式套管频域介电响应的影响

设计制作了10 kV油浸纸套管模型,对该模型进行电势分布仿真,得出电势沿径向路径线性分布的结论。同时,套管模型实际工频电容测量值30.197 pF与理论计算值30.172 pF接近,套管模型基本满足实际需求。测试了不同受潮程度下套管的主绝缘与绝缘油的频域介电响应特性后发现:受潮缺陷会使主绝缘的介质损耗和电容在整个频域(10~(-3)~10~3Hz)内明显增加;受潮后的绝缘油介质损耗在整个频域内明显增加,而电容则在10~(-3)~10~(-1)Hz频段内明显增加,10~(-1)~10~3Hz内基本保持不变。最后选取特征频率点(10~(-3)、10~(-2)、10~(-1)Hz)下的电容值与工频电容值的比值为特征量有效地实现了对套管受潮状态的评估,为频域介电响应技术应用于油纸电容式套管的状态评估提供了理论参考。     

Stability assessment of multimachine power systems using multivariable frequency response methods

Two feedback representations of linearized models of power systems are presented. One features torque loops and the other exciter loops. The torque loops representation is used to study damping and synchronizing torque coefficients. In the power system community, stability of linear models is associated with positive damping torques. Design of controllers is based on maximizing damping torques. A previous result that used the Nyquist criterion showed that in a single-machine infinite-busbar system a positive damping torque is sufficient but not necessary for the system to be stable. This result is stated briefly and generalized to multimachine power systems using the generalized Nyquist stability theorem. A multimachine system is used to demonstrate the results. The excitation loops are also investigated and the role of system zeros explained.     

Arc fault location: A nonlinear time varying fault model and frequency domain parameter estimation approach

In this paper a frequency domain formulation for nonlinear arcing fault location is presented. The proposed fault location formulation uses as input data first cycles after the fault inception voltages and currents. The formulation is based on circuit analysis and a parameter estimation method. To consider the main characteristics of nonlinear arcing faults, a time varying resistance embedded in a nonlinear model is proposed and used. The formulation is developed for the case of the most frequent single line-to-ground faults using phase components. The effects of fault inception angle, time-varying series resistance, source impedance, load flow, sampling frequency and others factors are investigated and analyzed. This new approach was successfully tested through computer simulation and real data obtained from a Southern Brazilian Energy Utility. The proposed method was developed as dedicated software and is currently used by CEEE-GT.