A wavelet approach for rms and harmonics measurements

This paper discusses the subject of root mean square (rms) of voltage or current and harmonic ratio value measurement problem in low voltage electrical apparatus testing system. A wavelet packet transform (WPT) method is introduced as a useful tool for detecting, classifying and quantifying the rms of testing waveform and harmonic ratio value. The proposed approach can measure the distribution of the rms of testing waveform with respect to individual frequency bands directly from the wavelet transform coefficients. The harmonic ratio value relative to basic frequency band can be calculated as well. The method is evaluated by its application to both analytical waveform and actual testing waveform data. The experimental results are offered to illustrate the performance of the proposed method.