Methods of Current Limitation in Low Voltage (up to 1 kV) Electric Networks

The article discusses and systematizes the causes of high values of short-circuit currents in electrical networks up to 1 kV and indicates their negative consequences. A brief analysis of some current limiting methods (both with and without additional investment) is given, which makes it possible to reduce the negative effects when significant short-circuit currents occur. The variants of the implementation of these current limiting methods recommended for study at the design stage or when replacing equipment that has exhausted its resource, are considered. The advantages and disadvantages of the methods of limiting short-circuit currents described in the article are indicated. Options for connecting equipment with low power consumption to nodes of the electrical network up to 1 kV with high values of short-circuit currents are also considered. Special attention is paid to current-limiting protection devices, a detailed description of the design of some of them is given, the advantages of their use in comparison with other current-limiting methods are indicated, the corresponding graphs of the limitation of the periodic component of the short-circuit current, shock short-circuit current and thermal pulse are presented. Based on the analysis of graphic materials, the issue of ensuring the selectivity of protections is considered. The degree of prevalence of equipment with the property of current limitation is determined. A method for determining selective current-limiting protection devices is given, viz. the method of energy selectivity, the corresponding graphs for determining energy selectivity are presented. The physics allowing to determine the degree of efficiency of limiting the short-circuit current is described. Recommendations on the use of current-limiting equipment are proposed.

The Method of Selecting Protection Devices in the Automated Design of an Electrical Complex of a Transport Vehicle

The article describes the mathematical and software module of computer-aided design of vehicle electric systems: selection and verification of protective devices. The following problems are solved: calculation of currents in the circuit sections of scheme for normal and directive modes taking into account the changes in the current distribution as to the modes of consumption, calculation of the currents in the circuit sections of design scheme for short-circuit modes, checking the correct choice of protection devices as to the rated current, checking the correct selection of protection device in overloads in case of electric motor loads, determining the sequence of triggering of protection devices in the modes of short-circuit and checking the selectivity of protection, checking the protection devices for resistance to short-circuit currents

Practical Aspects of Modernization of Electrical Equipment of the Substation

Currently, one of the important problems for domestic energy is the replacement of an outdated fleet of equipment at substations of electric power systems (EPS). The paper addressed the issue of upgrading the "Ice" substation in part of the selection of switches, checking the reliability of switches and the reliability of the substation in general. The substation characteristic is given, the changes in the main scheme of the substation electrical connections are substantiated, switches for all substation voltages are selected according to the current short circuit currents. To assess the degree of reliability of the selected switches, the substation is determined by their probability of refusal. Based on the assessment of the likelihood of failures and other equipment for the substation, the estimated time of trouble-free operation was determined, the average time of trouble-free operation and the average substation recovery time.

Ensuring Electrical Safety of a Mountain Quarry by Choosing Selective Relay Protection in the Electrical Networks with the Voltage above 1 kV

An important and urgent task is the calculation and choice of selective relay protection, which allows to ensure safe conduct of work in the conditions of mountain quarries. In the work, on the example of mountain quarry, the calculations were carried out for ensuring electrical safety of the consumers in case of emergency modes occurrence due to the appearance of short-circuit currents. At the same time, short-circuit currents in a 6 kV network, maximum current protection and current cut-off were determined, a selectivity map of protection operation was drawn up. Calculations show that with the correct protection settings, the required sensitivity coefficient is ensured in case of the short circuits at any point in the network. The selectivity map of relay protection is drawn up for a normal scheme, in which sectional switches are off at all the voltage levels. The inclusion of these switches does not affect the choice of the protection operation current, and only increases the sensitivity coefficient of the current protection and earth-fault protection. When arranging power supply schemes for the consumers, it is recommended: not to connect more than two consumers of EKG-4.6 or PKTP-400/6 type to the feeder supplying EKG-8; do not connect more than four consumers of EKG-4.6 or PKTP-400/6 type to a separate feeder; 6 kV quarry network and the boiler should be powered from different busbar sections of KRU-2 complete switchgear; it is advisable to have a cable network length of at least 5–6 km from one section of 6 kV KRU-2 busbars, which will increase the reliability of protection against single-phase earth-faults.

Features of asymmetric short circuit currents calculation in the elplek software product

In order to simplify the analysis of the electrical networks operation modes , specialized software tools for mathematical modeling of processes in them are used. There are many software products, but most of them are paid. To carry out research in complex power systems and obtain results in certain sections when performing practical and course work, as well as at certain stages of research, the authors actively use the free software product «Elplek», but in a deeper study of the software encountered certain features some parameters, which differ slightly from the generally accepted domestic method, which led to an error in the calculations in some versions of the schemes of power systems. The purpose of the research is to study the peculiarities of calculating the characteristics of asymmetric short circuits in the software product "Elplek" and to check the adequacy of the formed models. At the first stage, the object of research was chosen – this is a segment of the electrical network containing a small number of nodes and a theoretical calculation of the searched parameters of the short circuit mode in this segment of the electrical network was carried out. In the future, an approach was proposed on the task of parameters of elements in the software product "Elplek" and based on this approach, modeling was carried out as a result of which the results were obtained under the condition of the system's task, as sources of infinite power and calculations for the active part differ by 0.013%, and by reactive – 0.004%; subject to the task of the system, as sources of a certain power and calculations on the active part differ by 0.0046%, and on the jet - 0.0044%, which makes it possible to assert the feasibility of using the proposed approach in the analysis of indicators of emergency modes of complex schemes of electrical supply to consumers of certain segments of electric power systems. Features of calculation of characteristics of asymmetric short circuits in the Elplek software product are considered and the adequacy of the generated models is checked. Key words: power system segment modeling, Elplek software product, element parameter setting, single-phase short-circuit currents

Comparative Analysis of High-Voltage Power Line Models for Determining Short-Circuit Currents in Towers Earthing Systems

The article deals with the problems of single-phase short-circuit current distribution in overhead power lines. Short-circuit disturbances cause many negative phenomena in power networks. Since experimental studies of short-circuits in real networks are practically impossible to perform, these effects can be evaluated only theoretically, based on short-circuit current calculations with the use of appropriate mathematical models. Although short-circuit modeling is considered to be one of the simplest power system calculations, the exact mathematical description of the phenomena occurring at short-circuits is complex. Simplified normative methods are often used for short-circuit current calculations; however, this does not give ground for a thorough analysis of short-circuit current distribution in power lines. The distributions are analyzed using power line models with different degrees of complexity in line with the assumptions made for a given model. The paper presents the problem of current distribution analysis in high-voltage overhead lines for single-phase faults to the tower structures. Simulation studies were conducted on the models developed for the calculation of short-circuit currents in the high-voltage power line earthing. The objective of the analysis was to assess the validity of simplification assumptions followed by practical recommendations on the applicability of the models.