ДВУХСТОРОННИЙ МЕТОД ОПРЕДЕЛЕНИЯ МЕСТА ОДНОФАЗНОГО ЗАМЫКАНИЯ НА ЗЕМЛЮ В СЕТЯХ С ИЗОЛИРОВАННОЙ НЕЙТРАЛЬЮ

Abstract

Relevance Currently, on the part of enterprises operating 6–35 kV distribution networks, there is a request for a deep modernization of networks and the transformation of existing, outdated networks into digital ones. A separate aspect of modernization is the introduction of high-precision measuring devices and new principles of data transmission. At the same time, the probability of damage for various reasons remains. Single-phase earth faults in networks with isolated neutral are still the most common problem in distribution networks that do not have universal solutions. The problem is particularly acute with determining the location of single-phase earth faults. The opportunities provided by the introduction of digital networks can become the basis for the implementation of new algorithms for relay protection and determining the location of damage. Aim of research The article considers, developed by the authors, a two-way method for determining the location of damage in single-phase earth faults according to the parameters of the emergency mode when installing current transformers in all three phases. The two-way method of determining the location of damage is based on the use of zero-sequence currents and voltages, which are determined by calculation for phase current and voltage differences at the beginning and end of the line. The algorithm is focused on digital electrical networks equipped with high-precision measuring transformers and a communication channel. To calculate the parameters of the zero sequence, the differences of the phase emergency parameters at the beginning and at the end of the line are used. Research methods To develop and study a two-way method for determining the location of damage in single-phase earth faults, the principle of superposition in combination with the method of symmetrical components was used. Decomposition of three-phase currents and voltages into symmetrical components is a linear procedure. Therefore, the zero-sequence current in a three-phase line, in accordance with the superposition principle, can be represented as the sum of three zero-sequence currents, each of which is determined by one of the phase currents at zero values of phase currents in the other two phases. This application of the method of symmetric components is valid only for purely emergency values of phase currents. Therefore, in advance, the load current must be excluded from the phase currents of the emergency mode. Results It is shown that the use of the method of symmetric components for single-phase earth faults separately for the damaged phase and undamaged phases makes it possible to determine the zero-sequence current at the site of damage and the intrinsic zero sequence current of the damaged line. It is shown that this separation of the zero-sequence current makes it possible to distinguish two components of the zero sequence in the voltage difference at the ends of the line. Based on the allocation of two components in the current and voltage of the zero sequence, an algorithm for two-way determination of the damage location has been developed, which allows determining the distance to a single-phase earth fault in networks with an isolated neutral. To study the two-way method of determining the location of damage, a network model and a device for determining the location of damage were implemented in the MATLAB Simulink software package. A functional diagram of a two - way damage location detection device is presented. The performed studies on the model of the electrical network have shown the high accuracy of the proposed algorithm for determining the location of damage.