【作者】 王欢；

【导师】 苏鹏声；

【作者基本信息】 清华大学 ， 电气工程， 2003， 硕士

【摘要】 电力变压器是电力系统中重要的电气设备，它的安全运行直接关系到电力系统连续稳定的工作，因此对变压器保护算法的研究具有重要意义。微机保护利用计算机的信息处理功能，采用灵活的算法来获得保护的高速度和高灵敏度。本文围绕将小波变换应用到变压器的微机保护算法中，为保护算法提取所需的电气特征量方面进行了探讨。本文设计了以小波变换为基础的数字滤波器，对小波变换在微机变压器保护算法方面的应用进行了研究。针对一定谐波含量的信号，设计了将谐波分量分离的滤波过程，在此过程中引入采样率转换环节，配合小波滤波器实现不同频段信号的分离。同时对不同频段信号的分离采用不同的小波滤波器——共轭正交滤波器(CQF)与Daubechies(Daub)小波滤波器的滤波效果进行了比较和分析。如对于基波与二次谐波的分频，Daub6和CQF12滤波器对基波的滤波效果较好，而Daub6和Daub5对于二次谐波的滤波效果较好。为了验证滤波器的滤波效果，用半周傅氏算法对滤波前后的基波及各次谐波幅值的计算精度进行比较，滤波以后半周傅氏算法的精度有明显提高，计算误差在10%以内。本文提出了短窗Morlet复小波计算基波与各次谐波信号幅值的算法，并运用于变压器电气量特征提取。在电网频率波动情况下，通过比较说明短窗Morlet复小波算法在频率波动过程中具有比傅氏算法更稳定的特点，同时也可以达到1～3周波内完成的快速性。本文将短窗Morlet复小波的幅值算法应用于实际故障信号的特征量提取，证明了该算法的优越性。以Borland Delphi6.0为开发平台，开发了用于变电站自动化系统的可视化录波分析软件。该软件具有数据的图形显示、谐波分析、差动特性分析、阻抗特性分析和多功能计算器等功能，有助于用户根据需要观察保护特性曲线，为进一步的分析故障类型和判断保护动作正确与否提供依据。更多还原

【Abstract】 Power transformers are an important equipment in power system, the safe operation of power transformers has much effect on the continuous running of power system. So it’s valuable to research the algorithms of relay protection for transformer. Microcomputer-based protection uses the computer’s advanced signal processing function, which gives help in enhancing the protection algorithms’ operational speed and precision. This paper mainly focuses on the implement of wavelet to the Microcomputer-based protection for power transformer, especially to extract some useful information for the protection algorithms. A wavelet-based digital filter is designed in this paper, and the applications of wavelet to the protection for transformer are discussed. Aiming at extracting harmonic components of signals, a filter progress is designed. During the progress, the technology of sampling rate alteration worked as an aid in dividing different frequency signals. The wavelet filters adopted in the progress are the conjugate quadrature filter bank(CQF) and the Daubechies (Daub)based filter. Analysis and comparison of the results are made when different wavelet filters work. For example, to the frequency splitting between fundamental wave and second harmonics, the filter Daub6 and CQF12 do well in extract the fundamental wave, whereas the filter Daub5 and Daub6 do well in extract the second harmonics. To test the filter’s effect, the half-wave Fourier algorithm is used to calculate the amplitudes of harmonics. Through the filter progress, the errors of results are reduced compared with that are before the filter. The errors are less than 10%.An algorithm that can extract harmonics’ amplitudes using Morlet wavelets is put forward. Compared with the full-wave Fourier algorithm, the algorithm proposed in this article is more stable when the frequency of electric network flutters. Meanwhile the algorithm has the rapidity of giving out the<WP=5>results in one to three periodic times. This algorithm works effectively in extracting harmonics’ amplitudes of currents when transformer occurs exciting in-rush. A visual signal analyzing software that serves in transformer substation automation system is developed based on the programming language of Borland Delphi 6.0. The function of the software can be an aid to the field engineer in judging the working condition of transformers.更多还原