Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"Vitaliy LEVONIUK"

Mathematical modelling of transient processes in power systems considering effect of high-voltage circuit breakers DOI:10.15199/48.2019.01.13

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Gas circuit-breakers are used in high-voltage electrical grids [1]. Air-break circuit-breakers are part of some solutions. However, operation of these breakers involves a range of shortcomings, including: the need to operate compressors, considerable noise at the time of commutation, and large size [1]. These defects are absent from circuit-breakers of another type, where operating gas is replaced with sulphur hexafluoride - SF6. Its physical and chemical properties are better than of air since it does not react with materials of the breaker fittings, is not toxic or cause fire hazards. It is far smaller than equivalent air-break circuit-breakers. SF6 circuit-breakers are used both in new power facilities and in modernised power switching stations on a mass scale. ABB circuit-breakers using SF6 are the most common in highvoltage electrical grids.LTB 362-800 (T) E4 high-voltage circuit-breaker by ABB is analysed in this paper, quite common in the European countries. Each phase of the breaker consists of two modules connected in series. Each module comprises two pairs of contacts in parallel, to which capacitors are connected in order to distribute voltage more evenly. It is known [2] the time of arc burning in a circuit-breaker is affected by mechanical processes, in particular, the distance between contacts, dependent on the rate of their disconnection. Note gas pressure in the compression boxes, required to extinguish the arc, is generated only by mechanical means, without extra compression equipment [3]. Such circuit-breakers should have expanded drives to move contacts of the mechanism in order to overcome pressure in the circuit-breaker box, on the one hand, and to ensure necessary rate of contact movement in normal operation of a circuit-breaker. The fact pressure generated operates in the direction opposite to contacts’ movement, which gives rise to parasitic oscillations, is an important point in operation of [...]

Mathematical modelling of transient processes in power supply grid with distributed parameters DOI:10.15199/48.2018.01.05

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One of the key elements of energy systems is long power supply line with distributed parameters. All the power supply line relations are functions of time coordinate vs. spatial coordinate, this enforces use of complicated apparatus of applied mathematics while forming equations of line state, in particular, use of nonlinear differential equations with ordinary and partial derivatives. A very important issue concerning the analysed system is the fact that the power supply line is usually a component of one and only national energy system, which makes it necessary to establish very complicated boundary conditions for integration of telegraphers’ equations showing relations between voltage and current in any point of the power supply line at any moment of time. In most countries, power supply lines transmit direct and alternate current depending on the requirements. Direct current lines are used to transmit electricity to distant places at high rated voltage [3], [9]. However, electricity is transmitted most often using three-phase lines of alternate current [8]. The reason for this is simply the fact that electricity receivers requiring alternate current are most frequently accessible. Paper [4] presents design of mathematical model of two- and threewire power supply line, wherein analysis of processes of high voltage line 500 kV were made. With use of ATPEMTP software, high voltage lines’ breakdowns were studied. Practical approach to analysis of transient electromagnetic states occurring in power supply line are described in paper [6]. The authors present assumptions and requirements concerning modelling of separate elements of electric power systems (the energy system) in an innovative way. This article presents mathematical model of electric power system designed on the basis of interdisciplinary approaches. The main element of the system is power supply line with distributed parameters, linking two local [...]

Analysis of transient processes in a power supply system of concentrated and distributed parameters based on variational approaches DOI:10.15199/48.2018.12.33

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Application of mathematical apparatus to modelling of electrical power systems is virtually the most effective method. This approach finds extensive applicability in the case of power systems including long supply lines. Such a system generally consists of widely different parts: power plants, switching stations, supply lines, compensation systems, and a number of other elements [1]. Long power supply lines are key parts in electricity processing and transmission. High voltage lines between local power systems constitute inter-system connections. Fault currents, dependent inter alia on capacitances between wires, and leakage currents, which depend on electric charges on wire surfaces (corona discharge), must be considered in these lines. Current in line wires generates an alternating magnetic field that induces along a selfinduction SEM line. In addition, voltage between the line wires is not constant either. To address current and voltage variations along the line, it must be assumed each infinitely short wire section exhibits resistance and inductance, with capacitance and conductance between wires of that section. In other words, the line should be treated as a distributed parameters system [2]. In view of these conditions, use of ordinary and partial differential equations, including the telegraph equation, is recommended for analysis of transient processes in power systems. Their solution is not a problem. Both analytical and numerical methods are employed (D’Alembert’s, Fourier’s, reticulated, and other methods.) Finding boundary conditions for the telegraph equation as parts of the only system of general differential equations of a power system is the most complicated problem in analysis of transient processes in power systems, on the other hand. The theory of applied mathematics says Dirichlet first type, Neuman second type, and Poincaré third type boundary conditions serve to solve boundary probl[...]

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