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The necessity to develop analysis and calculation methods of nonsinusoidal modes in electric power networks is conditioned by the increasing number of electrical receivers parental to non-linear distortions (variable-frequency electric drive, LED-based lightning and so on). Higher harmonic components increase power and efficiency loss in current carrying parts, result in overheating of conductors and intense insulation deterioration, can cause resonance overvoltage and automation equipment malfunctions. Due to digitalization of the electric power industry it is necessary to develop methods of receiving, processing and digital communication on system state variables (currents, voltage, power), including nonsinusoidal modes. Wavelet transform is wider applied to analyze complex harmonic processes in electric power industry in conditions of transient modes. The paper introduces calculation methods of integrated indexes of electric power system modes – currents, voltage and power in the presence of electrical receivers with non-linear current-voltage characteristics. The method is based on Parseval equality and allows calculating via wavelet coefficients received by transformation of the initial stream of transient values of currents and voltages. Herewith the issue of data compressing is solved when transmitting digital information. The method allows determining the variables of every frequency component, interpreting the data in the three-dimensional scale (peak values, frequency and time) which will be used in choosing activities for higher harmonics filtration to reduce the loss in current carring parts.

The digital transformation of the electric power industry is one of the priority tasks for the development of the industry. Wavelet transform is widely used in the electric power industry to analyze the dynamics of complex non-linear non-stationary processes. The article proposes a method for calculating transient processes in electrical networks based on a recursive algorithm. The approximating and detailing wavelet coefficients of the discrete wavelet transform are used as the voltage signal. To select the optimal wavelet function, it is proposed to use a criterion that takes into account the accuracy of the signal recovery as a result of the inverse wavelet transform. The nature of the change in the calculation result with an increase in the number of iterations is shown. The results of a numerical experiment for a 110 kV network when calculating a three-phase short circuit showed an acceptable accuracy of the developed technique. The proposed technique makes it possible to compress the volume of transmitted digital data on normal and emergency modes of electrical networks.

Subject of research: methods for selective determination of an outgoing line with a single-phase earth fault based on the relative measurement of higher harmonics. Purpose of research: to develop a method for software filtering of high-frequency components and a method for identifying a line with a single-phase ground fault. Object of research: distribution networks 6-35 kV. Methods of research: wavelet-transformation of zero-sequence currents and voltages. Main results of research: the article proposes the idea of using the wavelet transform to organize software filtering of the zero-sequence current in order to increase the sensitivity of the admittance protection. On the basis of the wavelet transform, a modernization of the algorithm for determining a power line with a single-phase earth fault is proposed according to the principle of relative measurement of the energy of the spectrum of higher harmonics. The paper proposes to determine the energy of the spectrum by the wavelet coefficients of the discrete wavelet transform.