氧化锌避雷器泄漏电流检测的优化FFT分析

Optimized FFT analysis for leakage current detection of zinc oxide arrester

氧化锌避雷器泄露电流检测的实现,是通过谐波分析提取全泄露电流的各次频率阻性分量,依据其变化可判断该装置在电网中的运行情况。快速傅里叶变换(FFT)算法进行谐波分析时很难做到整数周期截断和同步采样,由此引入的频谱泄露和栅栏效应会影响谐波分析的结果,采用加窗和校正算法可以改善谐波频率、幅值和相位的提取精度。选用一种利用距谐波频率点最近的幅值最大和次大的两根离散谱线的比值以修正谐波参数的比值公式校正算法,同时利用窗谱函数推导出了谐波频率、幅值和相位的修正公式。这种算法能够有效降低频谱泄露和栅栏效应以及干扰给谐波分析带来的不利影响。基于该FFT的优化算法,推导了加汉宁窗函数的实用修正公式,通过仿真比较了不同窗函数修正算法的计算精度,并在实验环境下验证了加汉宁窗的比值校正算法的有效性和易实现性,且已应用于氧化锌避雷器泄露电流检测的实际工程中,利用该校正算法精确检测泄漏电流谐波阻性分量,对氧化锌避雷器运行性能进行诊断。

The realization of the leakage current detection of the zinc oxide arrester is to extract the frequency resistive components of the full leakage current through harmonic analysis,and the operation of the device in the power grid can be judged according to the change.Fast Fourier Transform( FFT) algorithm is difficult to perform integer period truncation and synchronous sampling in harmonic analysis.The resulting spectral leakage and fence effect will affect the results of harmonic analysis. Windowing and correction algorithms can improve the accuracy of harmonic frequency,amplitude and phase calculation. In this paper,a ratio correction formula for correcting the harmonic parameters using the ratio of two discrete spectral lines closest to the harmonic frequency point is selected. At the same time,the correction formula of harmonic frequency,amplitude and phase is derived by using the window spectrum function. This algorithm can effectively reduce the spectral leakage and fence effect and the adverse effects of interference on harmonic analysis. Based on the optimization algorithm of the FFT,this paper deduces the practical correction formula of the window function of Hanning,compares the calculation precision of different window function and correction algorithm through simulation,and verifies the ratio correction algorithm of Hanning window in the experimental environment. It is effective and easy to implement,and has been applied to the actual engineering of leakage current detection of zinc oxide arresters. Using the correction algorithm to accurately detect the variation of the leakage current harmonic resistive component,and diagnose the running performance of the zinc oxide arrester.