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Power quality (PQ) signals are the foundation of power quality analysis. Aim to get accurate analysis results, PQ signals should be recorded with high simple rate. Traditional power quality signal record methods with no data compression get a large amount of data set. It will cause the waste of memory space and difficult to transmit the data set. Wavelet transform is a very effective method for PQ signal compression. Therefore, this paper provides a status report of wavelet based PQ signals compression in the time-frequency domain through an overview of recent contributions. The results of the literature review indicate that power quality signals compression using wavelet transform is a very powerful tool and has been utilized in power system effectively. Wavelet-based compression methods using different types of wavelet transform and optimal wavelet thresholds have high compression ratio and reserve important details of original signals. The expectation is that further research and applications of wavelet will be widely applied in power quality signal compression.

Signal denoising is an important problem in the field of power quality (PQ) diagnosis of power system. Because the wavelet coefficients of noises are trending towards zero rapidly follow the scale increasing, the denoising methods based on wavelet transform have been widely applied. Threshold denoising method based on wavelet transform is an efficient method to reduce the white noise in the digital signal. There are two key problems need to be solved in practice. One is the optimization of the threshold; another is the determination of the decomposition order. This paper overviewed the theory of basis wavelet-based threshold denoising method and some kind improved soft-threshold theory, summarized their applications in the area of power quality signal denoising. All of results show wavelet-based threshold denoising method has great potential for PQ signals denoising. The analysis direction and emphasis of studying about the power quality (PQ) signal de-noising also put forward.