【作者】 史临潼；

【导师】 李冬辉；

【作者基本信息】 天津大学 ， 控制理论与控制工程， 2004， 硕士

【摘要】 发电厂、变电站中的直流系统接地故障检测的实时性和准确性对于保障电力系统的安全运行十分重要。目前广泛使用的低频信号检测法容易受到直流系统支路中存在的对地分布电容和环网的影响。针对这一问题,本文应用分形和小波变换的相关理论,在低频信号注入法的基础上提出了基于小波变换和分形理论的直流系统环网接地故障检测方法。研究的主要成果包括:1.总结了大电容接地和环网对直流系统故障检测的影响,并且深入分析了直流系统整流过程中的纹波电压产生的谐波环流和电流互感器饱和导致的采样信号畸变;2.在分析环网信号组成特点和深入了解分形理论和小波变换相关理论的基础上,提出利用分形的分维理论解决直流系统环网接地故障检测的方案;3.在仿真实验中发现2.方法中的不足,进而提出以小波变换和分形理论相结合的方法进行环网故障的识别;4.设计小波处理环节,选择了Morlet小波对信号进行频带划分,利用小波变换系数求取信号的另一重要特征——凹凸度参数;5.利用分形软件FD和仿真软件Matlab设计了算法程序,并通过大量的仿真计算进行了验证;6.搭建了模拟直流电网,初步实现了对现场实际数据的模拟。本课题的研究对于完善直流系统接地故障检测方法,提高直流系统运行的安全性、可靠性具有特定意义。同时,本文对于小波变换和分形理论在直流系统接地检测中的应用所做出的尝试性探讨,能够对未来的深入研究提供一定的帮助。更多还原

【Abstract】 It is important for power system to operate safely that DC system grounding faultdetection in power plants and substations is timely and exactly. The detection methodof low frequency signal injection widely used is easily influenced by the groundingcapacitors and the loop net. To solve the problem, this paper presents a new detectionmethod based on low frequency injection with wavelet transform and Fractal theory.The main contents of the research include:1. Summarizing the effects of grounding capacitors and the loop net to DCsystem grounding fault detection, and analyzing harmonious currents produced by theripple voltage during the process of commute and signal distortion influenced by CTsaturation;2. On the basis of analyzing the characteristics of signal in loop net and learningthe Fractal Theory and Wavelet Transform, a noval way of calculating the FractalDimension is used in loop net branch grounding fault of DC system;3. During the process of simulation, the scarcity of the way in 2 occurs. So areformative method that combines Wavelet and Fractal is used to identify loop netbranch grounding fault;4. Designing a part of signal transacting that uses Morlet Wavelet to partition thedifferent frequency and makes use of Wavelet Transform coefficient to calculateanother important parameter---concavo-convex parameter;5. Designing an algorithm based on the software of FD and Matlab, and testingthe feasibility through a lot of simulations;6. Setting up the simulating DC power supply net, primarily implementing thesimulation of real data of locale.This subject is very meaningful to perfect the detection of DC system grounding fault andrealize the safety and reliability of DC system. In addition, it helps the research of wavelet theoryand fractal theory in detection of DC system grounding fault in the future.更多还原