According to the characteristics of harmonic current caused by nonlinear load of power system,an approach to harmonic impedance assessment is proposed,which applies wavelet transform to process the disturbance signal of power quality and emphasizes the distorted signals.

On the basis, an analysis of the relationships between runout signal distortion, bit error length and foreign substances is given by numerical method.

For different types of disturbances,the proposed method can detect and recognize various instantaneous voltage distortion signals effectively such as instantaneous voltage sag,instantaneous voltage swell,instantaneous voltage impulse,instantaneous voltage interruption,harmonics and so on.