分类号学号M********* 学校代码10487 密级
硕士学位论文
学位申请人：谢梦
学科专业：高电压与绝缘技术
指导教师：陈俊武副教授
答辩日期：2012年1月6日
A Thesis Submitted in Partial Fulfillment of the Requirements
for the Degree of Master of Engineering
Research on Online Monitoring Technique for Low Frequency Signals of Power Net
Candidate：Xie Meng
Major：High Voltage and Insulation Technology哆来咪发唆电影
Supervisor：Asso. Prof. Chen Junwu
Huazhong University of Science and Technology小常识大学问
Wuhan 430074, P.R.China
Jan, 2012
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华中科技大学硕士学位论文
摘要
大容量、远距离输电和重负荷的互联电网阻尼系数较小，在系统受到扰动时，发电机转子之间会发生相对摇摆引发电网低频振荡，表现为输出电压上叠加了低频信号。由于XLPE电缆的tan 在0.01到1Hz频率段出现极大值且电压相关性明显，如果能够利用电网低频振荡产生的低频信号监测电缆绝缘老化情况，可以减小误差更加准确的反应出电缆的老化情况。为了验证该方法的可行性，本文以低频信号为研究对象，通过在线监测的方法研究低频信号的频率、幅值、产生频度、持续时间等特征。
本文在研究低频振荡产生机理的基础上，对电网四机两区模型进行了低频振荡仿真分析，得出该模型下电网低频信号特征以及低频信号在线监测中的难点。基于工频干扰大低频信号微弱的监测难点，对消除工频干扰的方法进行了研究，通过对各种陷波电路的仿真分析选取了适合本文消除工频干扰的前置电路。根据在线监测的要求，对常见数据处理方法进行了分析，通过对快速傅里叶变换的理论研究，巨各庄中学
确定了采样点数和采样频率并编写了数据处理子程序，达到测量低频信号的频率、幅值的要求。设计并研制了用于电网低频在线监测的装置低频信号监测仪，设计包括模拟电路和数字电路、抑电磁干扰、主程序以及各子程序的设计。
本文对低频信号监测仪进行了功能测试，测试结果与设计要求相符，满足在线监测的精度标准。设计了电网低频信号在线监测实验方法，但现场试验还需进一步完成。
关键词：低频振荡，低频信号，在线监测，消除工频干扰，低频信号监测仪
华中科技大学硕士学位论文
Abstract
The dumping coefficient of interconnection power grid with large capacity, long-distance transmission and heavy load is quite small. When this kind of transmission system is disturbed, relative movements occurs between the generator rotors, which lead to low-frequency oscillation of the power grid and low-frequency signal superimposed on the output voltage. Since a maximum value of tan of XLPE cable appears on the band of 0.01 to 1Hz frequency, using low-frequency signal, which generated by the low-frequency oscillation of the system, monitoring cable aging can reflect the agin
g of the cable. Therefore, this paper treats low-frequency signal as research object. Through on-line monitoring, the frequency, amplitude, duration and other features of low-frequency signal are studied.
Based on the generation mechanism of low-frequency oscillation, four-machine two-area model of the grid is established, which reaches the features of low-frequency signal and the difficulties when monitoring it. After that, frequency interference elimination method is studied; various notch circuit simulations are analyzed, and front end circuit which used to eliminate frequency interference is chosen. This paper also compares various data processing methods. Through analyzing fast Fourier transforming theory, sampling points and sampling frequency are determined, and data processing subroutine is programed to meet the demands of frequency and amplitude of the low- frequency signal. This paper designs and develops a low-frequency signal on-line monitor, including analog circuits, digital circuits, electromagnetic interference suppression, the main program and subprogram.
In this paper, functional tests of low-frequency signal on-line monitor are conducted. The test results are basically in line with the design, and the monitor can meet the accuracy requirements of on-line monitoring. Testing method of low-frequency signal on-line monitoring is designed, but field test need
s to be done in the future.
Keywords：low-frequency oscillation，low frequency signals，online-monitoring，weak signal detection，low frequency signals monitoring device
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