Background: Dynamic modes of various nonlinear electromagnetic devices regarding instantaneous currents and voltages are now calculated by numerical methods. That is why the software package MATLAB, a high-level programming environment, has become widely spread. However, its built-in features are not always sufficient to describe circuits containing non-linear electromagnetic devices, in particular three-core transformers. It becomes clear while studying asymmetrical transients which are caused by changing parameters of the transformer itself, such as breakage or short circuit of windings, or by using a connecting load. Asymmetric transients of transformers are normally analysed by the method of superposition of forced and free modes. And the forced mode is calculated by the method of symmetrical components, while the available free components are determined by introducing different coefficients identified by comparing the accumulated experimental and calculated data. This approach is based on rather rough assumptions. The goal of the present research is to develop methods, algorithms and programs which allow us to use Simulink for calculating nonlinear electromagnetic devices. Materials and methods: The study of dynamical modes in the transformer was performed by the alternating direction method in MATLAB environment that has a program for calculation of nonlinear magnetic circuit of the three-core transformer.  «Вестник ИГЭУ» Вып. 4 2016 г.  ФГБОУВО «Ивановский государственный энергетический университет имени В.И. Ленина» 12 Results: A model and algorithms have been developed extending the capabilities of Simulink for the calculation of circuits with non-linear electromagnetic devices. The asymmetrical modes for the three-core transformer with a Y/Yn winding connection scheme have been calculated. Conclusions: The proposed model is universal and allows analysing transient, steady-state and emergency modes under asymmetric loads in transformers with different connection diagrams. The evaluation was made by verifying the results of numerical experiments against the passport data of the transformer.

/pdf/matlab-analysis-of-dynamic-modes-of-three-phase-three-core-4pwxes9b0v.pdf

MATLAB analysis of dynamic modes of three-phase three-core transformers

The considered improvement of qualit y of the risofraph print based on a mathematical model in the environment Matlab by using the specialized algorithms and digital filter of the Image Processing Toolbox. Use the model of screen printing in Matlab environment for risograph provide an opportunit y to improve the qualit y of prints by adjusting profile risograph to a specific view and the t ype of digital image. The use of the proposed technology will reduce the flow of the film and the paint by eliminating printing test prints and reducing the time spent printing.

/pdf/kompiuternoe-modelirovanie-i-povyshenie-kachestva-bwwlmobxfh.pdf

Компьютерное моделирование и повышение качества ризографической печати

/pdf/development-of-the-design-and-design-technique-for-high-4t5j0ou1nn.pdf

Development of the design and design technique for high-frequency transformers with an amorphous alloy core

One of the areas of industrial digitalization is associated with the concept of digital twins, which allows simulating the operation of real devices in various modes. Currently, simulation packages such as MatLab Simulink, or physical field modeling systems, such as ANSYS Maxwell are applied. The problem is that, despite the declared accuracy, practically no model of a technical device can demonstrate a point-to-point correspondence of the simulation results and the experimental results, especially under transient conditions. It is caused by variations of material characteristics and difficulty to consider technological factors. The purpose of this article is to develop a method to revise the simulation model of a single-phase transformer. So, this model can provide 95 % accuracy of the coincidence of the instantaneous values of currents in the windings when simulating the operation of the transformer both in steady state and in transient modes. The authors have used the methods to model electrical circuits, simulation modeling using the MatLab Simulink SimPowerSystem package, experimental methods to record current and voltage oscillograms. The authors have studied the possibility of accurate modeling of transient and steady processes in a single-phase transformer, considering the nonlinearity of the magnetic properties of electrical steel and the mutual influence of magnetic fluxes of windings that close outside the magnetic core. To revise the model, a multichannel high-speed recorder developed by the authors has been used. A technique to revise a simulation model of a single-phase transformer using experimental oscillograms of voltage and no-load current has been developed. Application of the proposed method to revise the transformer magnetization curve using experimental oscillograms of a real transformer, as well as calculating the resistance of the parallel magnetization branch of the equivalent circuit of the transformer based on the oscillogram, makes it possible to obtain an almost point-to-point correspondence of the no-load current curve obtained when modeling with the experimental curve. The proposed technique to develop a simulation model gives more accurate results of modeling transient modes of transformers in comparison with analogues.

/pdf/method-to-revise-a-simulation-model-of-single-phase-1zq2jihn.pdf

Method to revise a simulation model of single-phase transformer using no-load current waveforms

We develop a simplified model of a current transformer based on its current-voltage characteristic. This model is applicable for studying relay protection operation in transient conditions when no high accuracy or consideration of current transformer magnet core hysteresis is required. The model was developed in MATLAB Simulink using elements of the SimPowerSystems and Simscape libraries. The model uses the transformation ratio and current-voltage characteristic obtained during operational tests of a current transformer. Calculation experiments with non-linear resistance found that a currentvoltage characteristic of voltage and current values can be used to model a current transformer, rather than instantaneous values. The following conditions were simulated: for nominal currents in current transformer windings to check the transformation ratio; for opened secondary winding; with current transformer saturation by increasing secondary loading; increasing the primary current ratio and presence of aperiodic current at the start of the transition process. It was found that the developed current transformer model allows for a correct imitation of all the above conditions. To verify the model, secondary current oscillograms were obtained using real current transformers 10 kV at known primary current, which were compared with nominal oscillograms in the model. The discrepancy between the results of calculational and real experiments was no more than 10% in amplitude values, with high-quality matching obtained for current charts in the model and real current transformers. A significant advantage of the developed model is that its setting requires no information on magnet core cross-section, power line length, steel grade, and the number of current transformer winding turns.

/pdf/a-simplified-model-of-a-current-transformer-for-studying-gg7eew7pu3.pdf

A simplified model of a current transformer for studying relay protection operation in transient conditions

The use of amorphous ferromagnetic alloys in transformer construction allows reducing no-load losses by 4 times or more. At the same time, the magnetization curve of amorphous steel has a shape that is close to a rectangle, which significantly distorts the shape of the no-load current curve. This is accompanied by inrush current increases when a saturated transformer is turned on. However, there are no publications devoted to this issue in the periodicals. The purpose of this work is to develop a dynamic model and study the dynamics of an amorphous steel core single-phase transformer (TAS) operating at an arbitrary external load. The calculation of the electrical circuit was made by a one-step method based on a modified 2nd-order Rosenbrock formula, and the circuit parameters were calculated by the finite element method. We have developed dynamic models of the single-phase transformer based on the use of controlled current sources and EMF and implemented in the MatLab Simulink SimPowerSystem. These models allowed us to take into account the effect produced by the practically rectangular shape of the magnetization curve of the amorphous steel used to make the core on the operation of a saturated transformer. It has been established that the inrush current occurring when a saturated TAS is switched on can exceed the rated current tenfold. A significant distortion of the current curve has been detected in the first periods even when the transformer operates at nominal load. The developed models can be used to study the operation of a transformer at an arbitrary load. These models can be developed further. It has been found that a significant effect on the transformer operation is produced by the shape of the amorphous steel magnetization curve.

/pdf/development-and-study-of-a-dynamic-model-of-single-phase-3n248j2yw6.pdf

D.E. Dryazgov

Papers

Development and study of a dynamic model of single-phase amorphous steel core transformer