Power line communication on smart grids installation with distributed energy resources (DER) produces electrical noise that may have a serious impact during communication. Also a high level of electrical noise may cause fault measurement and generation of control data may lead to the loss. One of the crucial problems in the steady operation of distribution networks, in the frequency range 2-150 kHz harmonic emissions or supra-harmonics (SH). In this study, the results of experimental studies demonstrate the origin of these distortions. The proposed discrete wavelet transformation method can help to find a solution for SH components.