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The article discusses an algorithm for determining the fundamental harmonics of currents and voltages in the measuring devices of relay protection at saturation of the magnetic circuits of current transformers. The aperiodic component arises due to the presence of complex resistances of generators and power lines in the parameters of the power system. Periodic components appear in microprocessor technology due to imperfection of the measuring devices. The exclusion from the short-circuit current entering the measuring devices of relay protection, non-periodic components and harmonics, except for the first one, makes it possible to increase the reliability of relay protection.

The paper addresses the problem of relay protection malfunction under the condition of saturated state of the current transformer magnetic core. The first part of the paper provides an overview on how this problem is solved in the related studies. The pros and cons of the existing approaches are highlighted and discussed. A method for reducing the influence of aperiodic components on the operation of digital relay protection is considered in detail. An algorithm for eliminating the aperiodic component in the current of the measuring element relay protection, caused by the saturation of current transformer cores, is shown and described as a simple step-by-procedure, providing the opportunity of its real-time applications. The authors focus the discussion and concluding remarks of the paper on the major advantages and the promising application spheres of the proposed approach. All the calculations provided in the case study section are based on real metering data.

The authors propose the algorithms to calculate the actual values of currents and their derivatives. The algorithms allow a sharp reduction in the aperiodic components of currents in the calculated actual values and their derivatives. The algorithms are developed to calculate the instantaneous values of positive- and negative-sequence currents when the information obtained during a time interval equal to two milliseconds or less is used. An algorithm is devised to calculate the sinusoidal components of the currents in the presence of aperiodic components in the samples. To eliminate the disoperation of digital relay protection and improve the accuracy of fault location, it is necessary to eliminate the influence of aperiodic components in the currents drawn to the measuring devices of relay protection. The algorithm completely eliminates the aperiodic component at any time constants and is implemented by four samples of currents. The four samples of currents separated by three sampling intervals are sufficient for calculating all the parameters of currents, including the positive and negative-sequence currents, in particular in the case when the magnetic cores of current transformers reach saturation. The proposed methods for setting the industrial frequency parameters to avoid the aperiodic components in short-circuit currents are based on the algorithms that process the data from three and four samples of currents.

The paper presents the principles of constructing simulation models of the components of an integrated multi-energy system based on the energy hub concept. The application of the algorithms designed to develop simulation models of the components are given, the results of their implementation are verified with generally accepted theoretical approaches used to obtain the necessary characteristics depending on the set objective functions. The proposed approach offers a broad prospect for the study of many significant problems in integrated power systems with multiple carriers, including their properties, features of expansion and operation

In addition to periodic components of industrial frequency, the aperiodic ones arise in windings and on the generator output leads under the conditions of shortcuts. These aperiodic components slow down the operation of the main differential protection of a generator up to ten periods of a network frequency with the application of saturated magnetic cores of current transformers as well as zero current relays and transformer differential protection [1]. This slowing down promotes accidents and can even lead to generator’s winding and steel burn-out at high-ampere currents. The present paper considers the ways to reduce the impact of aperiodic components on the operation of digital relay protection of generators and generator-transformer blocks and proposes generator’s directional digital protection.

The introduction of microprocessor technology in the management of energy objects, including diagnostics, into relay protection and automation, allows combining and unifying relay protection of individual objects into a single system. One of the methods of unified relay protection may be directional protection. It is possible to develop and offer directional protection for generators, transformers, which are currently not used. An obstacle to the use of directional protection of generators and transformers is the presence of aperiodic components in the short-circuit currents, that introduce distortions in determining the angle between the short-circuit currents and voltages. At the “Power Supply” Department of the North-Eastern Federal University named after M.K. Ammosov a method that excludes aperiodic components in the secondary currents of current transformers of power system objects was developed, which made it possible to exclude incorrect actions of directional protections, including when saturating the current transformer magnetic cores. The method is based on processing four instantaneous samples of currents separated by identical sampling intervals.