In recent years, with the development of computer science and mathematical theory, many new ideas and technological routes have appeared in the field of relay protection. Wavelet analysis technology, adaptive technology artificial intelligence technology, fuzzy technology, and expert systems are widely used in power systems. Relay protection, and has made encouraging results This paper only describes the application of wavelet analysis in relay protection of power systems.
1 Application of wavelet analysis in relay protection 1.1 The basic concept of wavelet analysis Wavelet analysis is a new mathematical analysis method that draws on modern analytics such as functional analysis, numerical analysis, harmonic analysis, Fourier analysis, spline The essence of many branches, such as analysis, is the perfect combination of pure mathematics and applied mathematics after Fourier analysis. The idea of ​​wavelet analysis first came from the field of signal analysis. For a long time, both mathematical and signal analysis circles are constantly seeking a Time domain and pure frequency domain combination of the two methods of analysis, so there is the idea of ​​time-domain localization analysis, that is to provide a signal in the time domain and frequency domain of localized information This method is wavelet analysis.
The essence of wavelet analysis is the wavelet transform of the signal. The wavelet transform can be understood as: A discrete signal is represented by a group of wavelet functions with different scales and positions. Usually, these wavelet functions are the fundamental wavelet wavelet which is an oscillation. Beijing Tsinghua East Road No. 17 China Agricultural University 1 (East Campus) 60 Mailbox, 100083 Waveforms, Up to a few cycles The given wavelet has a definite position and scale, and is particularly suitable for expressing discrete or singular signals or image wavelets. There are many different types of wavelets. Orthogonal wavelet mono-orthogonal wavelets, biorthogonal wavelets, wavelet packets, etc. have been discovered. In the future, it will continue to find new practical wavelets because of their perfect theoretical and practical value. The favored application in power systems has received widespread attention. These applications include line and component protection, line fault location, power equipment condition monitoring and fault diagnosis, harmonic analysis, transient stability analysis, dynamic safety analysis, and neural networks. And expert systems, anti-electromagnetic interference load forecasting and HVDC transmission system 2 Application of Wavelet Analysis in Transformer Relay Protection Power system transient signal processing traditionally uses Fourier analysis. With the deepening of research, the Fourier analysis method can not meet the requirements of describing the abrupt part of the signal, and the wavelet analysis method provides an effective way to deal with non-stationary and sudden singular signals. Power transformer is an important device in the power system. Failures will have a serious impact on the reliability of the power supply and the normal operation of the entire system. The key problem of transformer protection is still how to identify the inrush current and short circuit current. There are many ways to identify inrush current, and each has its own advantages and disadvantages. In recent years, domestic and foreign scholars have put forward many new principles for identifying inrush current, such as magnetic flux identification method equivalent circuit parameter identification method, but these principles need to make artificial assumptions on certain parameters of the transformer, and its prospect depends on Further theoretical breakthroughs At present, it is still the second-harmonic braking principle and waveform discontinuity angle principle that are widely used in engineering. According to recent reports, these two principles are in some cases (such as modern ultra-high-voltage and large-scale Capacity transformers have certain limitations. In the field of relay protection, theoretically speaking, the wavelet analysis method should be able to identify the reflected waves of the faults that are required for the transient traveling wave in fault location and effectively strip the reflected waves. Noise signal, and then measure the location of the fault.
2) The use of current traveling wave for fault location is feasible. According to another report, the accuracy of wavelet ranging has reached about 100m. Therefore, it can be seen that wavelet ranging has good prospects for development.
1.5 Application of wavelet analysis in automatic reclosing Automatic reclosing is an effective measure to improve the reliability of power supply to ensure the safe and stable operation of the power system. Wavelet analysis is applied to the automatic reclosing of transmission lines to identify instantaneous faults and permanent transmission lines. Failure, made a useful attempt Analysis shows that it is a promising method 1.6 Application of wavelet analysis in signal filtering The purpose of filtering is to obtain the attenuation of the amplitude and phase of the fundamental wave and each harmonic component. For the transient and short-circuit signals of the DC component and each harmonic component, the Fourier transform cannot accurately calculate the amplitude and phase of a certain moment; when the oscillation occurs, the system frequency cannot be maintained but appears as a function of time. Fourier transform will also encounter difficulties.
246 Cai Chaohao, Li Chuan. Use wavelet transform to distinguish between oscillation and short circuit. North China Electric Power Technology, 1999. (4): 16-187 Dong Xinzhou, Sui Zhongxing, Ge Yaozhong, et al. Application of Wavelet Transform in Fault Signal Analysis of Power System . Chinese Journal of Electrical Engineering, 1997, 17 8 Dong Xinzhou, Ge Yaozhong, Xu Bingyi. Study on Fault Location of Transmission Lines Using Transient Current Traveling Waves . Chinese Journal of Electrical Engineering, 1999,19 (4): 9 Cai Chaohao. Adaptive Reclosure Based on Wavelet Analysis. Northeast Electric Power Technology, 1999 (3): 10 Yang Hua, Ren Zhen, Tang Zhuoyu. A New Method of Detecting Harmonics Based on Wavelet Transform . Automation of Power Systems, 1997, 21 (10): 39-4211 FANG Fengmei, SU Peipu. Application of Wavelet Transform in Detection of Ground Fault in Distribution Automation System . Power System Automation, 1999, 23 (13): 12 F. Feng Mei, Su Peipu, Xia Ruihua. Application of Wavelet Transform in Detecting Ground Fault of Small Currents . Power Automation Equipment, 1999, 19 (3): 8-1113 Yang Xiaomin, Li Hongyan, Wang Yanli. Using wavelet principle to construct relay protection starting element research. Power Automation Equipment, 1999, 19(4):
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