Digital Algorithm of Wavelet Transform and Its Application on Protection for Extra High Voltage Transmission Lines
Ha Hengxu,Zhang Baohui,Lü　Zhilai
(School of Electrical Engineering,Xi'an Jiaotong University,Xi'an 710049,China)

Abstract: The digital algorithms of integral and discrete wavelet transform are presented for purpose of electric powersystem protection, based on the analysis of wavelet transform for sampled digital signals under the Shannon sampling theorem. The relationships between the error of wavelet transform and the characteristics of wavelet and scaling function are additionally studied and the results show that the error of wavelet transform calculation mainly depends on calculation of the projection of signal in scaling space and on the selection of wavelet．Ｔhe better time-frequency character of wavelet selected，the more precise in wavelet transform. The introduction of the wavelet application on traveling wave protection and transient based nonunit protection for extra high voltage (EHV) transmission lines is also presented in detail.
Keywords: integral wavelet transform;discrete wavelet transform;extra high voltage transmission lines;traveling wave;non-unit transient protection