Abstract: The purpose is to analyze the similarity of the reaction of the power line at the random variations of voltage, frequency and phase angle in the permanent mode of the power line in alternating current. The research is based on the application of the theory of modulation of electrical signals in radio circuits. The possibility of analyzing the variation processes with the model of the single-tone modulator signal was argued. It has been shown that the similarity of the power line reaction to amplitude modulation or angular modulation is determined by the identity of the harmonic spectra of the modulated signal, regardless of the physical essence of the modulation process. The upper limit of the modulator signal frequency are below the frequency deviation limit of the power system.