Showing papers by "Ivanovo State Power University published in 2020"

Development of a nonlinear model of a three-phase transformer to study the effect of asymmetry of the magnetic system on the operation of the device in arbitrary modes

Abstract: Currently, when designing power transformers in order to take into account the influence of the asymmetry of the magnetic system on the operation of the device, especially in transition modes, engineering analysis packages based on field models are increasingly being used. However, such models are slow. At the same time, dynamic transformer models based on the magnetic circuit model are not inferior in accuracy to field models. Existing chain models of a three-phase transformer either do not take into account the asymmetry of the magnetic system or poorly integrate with simulation packages. The purpose of this article is to develop a dynamic model of a three-phase transformer which would allow considering the design features at the design stage, in particular, the asymmetry of the magnetic system and the influence of these features on arbitrary modes of the device operation. A contour current method was used to calculate a non-linear magnetic circuit of a three-rod transformer, and a single-step method based on a modified 2nd order Rosenbrock formula was used to calculate the electrical circuit. A nonlinear dynamic model of a three-phase three-core transformer based on the use of controlled current sources and EMF has been developed. This model is able to integrate with simulation packages including MatLab Simulink SimPowerSystem. The model allows taking into account the influence of the asymmetry of the magnetic system on the transformer operation in various operating modes including emergency and asymmetric ones. The novelty of the developed model can be seen in the approach to constructing a nonlinear matrix of magnetic resistances without explicitly using inductance matrices, which increases the accuracy and stability of the model considering the asymmetry of the magnetic system. The curves of transients in the characteristic operating modes of the transformer are given. The developed models can be used in the design of power transformers, including specific ones. They enable to increase the accuracy of the verification calculation and bring it to the level of simulation modelling. These models can also be applied for constructing digital twins of power transformers taking into account the influence of the design features of transformer equipment on the operation of power grids.

The development of multi-channel control system for a multi-phase synchronous electric drive with improved vibration noise characteristics

Abstract: Constantly increasing requirements for the performance of electromechanical systems include the task of improving the vibration and noise characteristics of the electric drive. Currently, this problem is solved mainly by using traditional three-phase systems. The transition to a multiphase version of the electric drive construction opens up new opportunities for its solution. The aim of the study is to improve the vibration and noise characteristics of the electric drive through the development of a multiphase control system that provides targeted formation of the field configuration in the gap of a multiphase electric machine. To conduct the research, the model of a multiphase synchronous motor proposed by the authors was used. The model considers the spatial non-sinusoidality of the field distribution in the gap and enables to represent the engine as a set of parallel substructures, the number of which depends on the number of phases. The technique to design a synchronous motor with an arbitrary number of winding phases based on the field model of the machine has been proposed. The correctness of the results obtained is ensured by the real geometry of the magnetic circuit and steel saturation. The multi-channel control system of the electric drive, characterized by the targeted formation of field configuration in the gap of a multiphase electric machine has been proposed. The calculation model of the electric drive has been developed. The model combines the field model of the engine and the control system. The engine model is implemented in the ElСut software package, the control system model is implemented in the MatLab (Simulink) complex. Compared to the traditional three-phase design of the electric drive with a sinusoidal supply voltage, the options for forming a field in the gap of a synchronous motor considered in the article provide a reduction in ponderomotive force by 8–14 %. The engineering methodology for designing an m-phase synchronous permanent magnet motor with permanent magnets and the structure of the multi-channel control system can be applied when developing electric drives with improved vibration and noise characteristics.

A cell model of heat conduction in multi-layer medium with variable number of the layers

Abstract: The heat conduction is an important part of heat transfer processes in power engineering, civil engineering, chemical technologies, etc. Variety of researches is devoted to theoretical and experimental study of the heat transfer by the heat conduction. At present, the considerable attention is concentrated on the heat conduction in media with variable boundaries (the so-called Stephan’s problem). A reason of a boundary motion can be burning-out of material, its wear, its melting with carry-over of a melt, other physic-chemical processes. Analytical solutions to the Stephan’s problem exist only after far-going assumptions, which lead to the loss of their practical value. The development of effective numerical methods of its solution becomes an actual scientific and practical problem. Such methods are to combine universality and physical clearness and convenience for engineering practice. In order to solve the problem, the method of mathematical modeling is used. The model uses the mathematical tools of the theory of Markov chains. It is adapted to the cell model of a medium, in which the number of cells can vary due to this or that mechanism of the edge cells interaction with outside medium. The heat transfer by the heat conduction and the heat interaction with the heat sources are described by the classical heat balance equations. The study of the influence of parameters on the process is performed by numerical methods. A mathematical model that allows describing transient heat processes in a multi-layer medium with variable number of layers is developed. The results of heat process calculation inside a plane wall with the moving boundary form the heat source side due to the boundary thermal distruction at a certain critical temperature are presented. The obtained results are physically consistent and approve the model workability. The principle differences between the heat processes in the walls with immovable and movable boundaries are found. It is shown that the temperature in a wall with moving boundary does not overbalance the critical temperature of the thermal distraction when the wall still exists, and the rate of the wall dimension decrease is growing with its dimension decrease.

Mathematical simulation of extra-high voltage overhead transmission lines for travelling-wave-based relay protection devices

Abstract: The complexity of transient processes during travelling-wave propagation in extra high voltage overhead lines is deter-mined by the fact that many frequency components are presented in the electromagnetic wave front. For the correct analysis of the aforementioned transient processes and for further development of travelling-wave-based relay protec-tion and fault location devices, it is necessary to take into account the parameters of the environment where electromagnetic wave propagation occurs. For the transmission line, these parameters are longitudinal inductance, longitudinal resistance, shunt capacitance and shunt resistive conductance. It is worth mentioning that for a variety of reasons unit-area longitudinal inductance and resistance are the parameters which depend on frequency, thus travelling wave velocity is different for different frequency components of the electromagnetic wave front. The popular researches which address this problem either fail to consider the dependence of overhead line inductance and resistance on frequency or this dependence is considered approximately for the high-frequency range, which can cause significant errors in the transient processes analysis during travelling wave propagation. In view of this, the development of the approach to overhead transmission lines simulation, which will allow both determining the line parameters in a wide frequency range and evaluating steady-state behaviour and transient processes in long-distance transmission lines, arrears relevant. The main research method to establish extra-high voltage transmission line parameters employs the simulation study in COMSOL Multiphysics. A number of assumptions were made in the simulation process: homogeneous soil layer, entire transmission line section and absence of transmission line conductor sag. The usage of finite elements method (FEM) for differential equation solution in the above-mentioned software is also seen as an assumption. The approach to extra-high voltage transmission lines simulation has been offered. This approach consists of the usage of Maxwell’s equations in combination with numerical integration with finite elements method (FEM). Frequency response for transmission line parameters and travelling-wave propagation velocity rate for different frequency components have been obtained. The results obtained can be used in updating of electrical power system models for further research in the relay protection field. The suggested approach will allow evaluating line parameters of other voltage types and obtaining more accurate values of transmission line parameters and travelling wave propagation speed along transmission lines for high-frequency range. The use of these transmission line models will enable to formulate approaches to improve the existing algorithms of travelling-wave-based relay protection and fault location devices.