【作者】 张小丽；

【导师】 曾祥君；

【作者基本信息】 长沙理工大学 ， 电力系统及其自动化， 2008， 硕士

【摘要】 随着电力系统规模的扩大,输电线路故障定位和继电保护变得越来越重要。电网故障产生的暂态行波信号,沿输电线路以接近光速的速度传输到电网中各变电站,在各变电站记录故障行波到达的精确时间和波形特性,可以进行故障行波定位和行波保护。故障行波定位和行波保护不受CT饱和、系统振荡和故障电阻等因素影响,具有定位精度高、保护动作速度快等优点,故障行波定位和行波保护已成为国内外研究的热点。但行波信号变化速度快,信号特征提取困难。为此,本论文利用希尔波特-黄变换(HHT)对故障行波信号进行分析,提出了新型行波定位和保护方法。论文首先阐述了输电线路行波的基本理论;针对行波定位的关键问题---故障时刻的准确提取,提出了利用HHT方法来检测和分析故障暂态信号的方法。通过经验模态分解法(EMD)提取故障行波信号的固有模态函数(IMF),再进行Hilbert变换,得到各自的瞬时频率,由瞬时频率进行行波到达时刻的准确检测;希尔波特-黄变换与小波变换比较,不存在变换参数的选取难题。论文对一实际的电力系统进行了仿真,并将该方法与小波变换进行了仿真比较,结果表明:采用希尔波特-黄变换提取电网故障行波波头到达的时刻最精确,故障定位精度最高。论文还对输电线路上的阻波器以及不同的母线分布电容对行波传输的影响进行了详细仿真分析,对比分析了输电线路区内故障与区外故障产生的故障行波信号频率特性的差别。由希尔波特-黄变换计算变电站电压行波波头的频率,利用输电线路两端变电站电压行波波头频率的比值进行线路内部故障判断。经理论分析和EMTP仿真验证,该行波保护方法具有保护精度高、选择性和可靠性好等优点。更多还原

【Abstract】 With the development of power systems, fast and accurate faults locations and protections become more and more important. Power grids produce transient travelling wave signals, which transmit along the transmission line to each substation with the speed approaching the velocity of light. Using the exact arrival time of the fault traveling wave and the waveform characteristics recorded at each substation, the traveling wave based fault location and protection can be realized. The fault location has high precision, and the protection has fast action speed. They cannot be influenced by current transformer saturation, low frequency oscillation and fault resistance. Traveling wave based fault location and protection thus become a hot research area in the world. Whereas, the traveling wave signals variation is quick, and the signal characteristics are difficult to extract. In order to improve them, Hilbert-Huang Transform is applied to analyze the fault traveling waves, and a new traveling wave based faults protection and location method is proposed in the thesis.The thesis first analyzes the theory of traveling waves on transmission lines. In view of the key problem of traveling wave fault location—the fault time accurate recording, a novel time-frequency analysis method for the traveling wave signals is proposed. Hilbert-Huang Transform (HHT) is applied to detect the signals. Intrinsic Mode Functions (IMF) of traveling waves are extracted by Empirical Mode Decomposition (EMD), and then Hilbert transform is applied to calculate the corresponding instantaneous frequency of each IMF component. The arrival time of traveling wave can be detected by the instantaneous frequency. Comparing with Wavelet Transform, HHT is not necessary to select parameters and has only one result. Power grid faults locations are simulated, and the faults generated traveling waves are extracted by wavelet transform and HHT respectively. Results show that traveling wave arrival time extracted by HHT algorithm is more accurate, and the fault location accuracy is higher.The influence of substation equipments ground distributed capacitance and transmission line trappers on the traveling wave propagation characteristics is simulated. The characteristics difference caused by internal faults and external faults of transmission line is analyzed. A new traveling wave based transient protection using the frequencies ratio of the two end voltage traveling waves of the transmission line is proposed. The frequency is obtained from HHT.. EMTP simulation results show that the protection is with high precision, good selectivity and reliability.更多还原