Static Mode Of Operation Research Articles

Development of a dynamic mathematical model of PEM electrolyser for integration into large-scale power systems

Proton exchange membrane (PEM) electrolyser stands as a promising candidate for sustainable hydrogen production from renewable energy sources (RESs). Given the fluctuating nature of RESs, accurate modelling of the PEM electrolyser is crucial. Nonetheless, complex models of the PEM electrolyser demand substantial time and resource investments when integrating them into a large-scale power system. The majority of introduced models in the literature are either overly intricate or fail to effectively reproduce the dynamic behaviour of the PEM electrolyser. To this end, this article aims to develop a model that not only captures the dynamic response of the PEM electrolyser, crucial for conducting flexibility studies in the power system, but also avoids complexity for seamless integration into large-scale simulations without comprising accuracy. To verify the model, it is validated against static and dynamic experimental data. Compared to the investigated experimental cases, the model exhibited an average error of 0.66% and 3.93% in the static and dynamic operation modes, respectively.

Characterizing Reversible and Irreversible Degradation Effects of PEM Water Electrolyzer Stacks

Polymer electrolyte membrane water electrolyzers (PEMEL) have been identified as a key component in a decarbonized large-scale energy system, as they can produce high-purity hydrogen from renewable electricity sources for the chemical industry or energy storage. However, the long-term durability and performance of PEM electrolyzers remain a major challenge, with degradation being a critical factor that limits their lifespan and efficiency. Recent studies have focused on developing accelerated stress test (AST) protocols for PEM electrolyzers to better understand the conditions and mechanisms that lead to degradation.1, 2 Especially the reversible rise in cell potential, which in the literature is often regarded as apparent or reversible degradation, must be further investigated to find mitigation strategies for operation.3, 4 We present our research on the development of two testing protocols (static, dynamic) characterizing reversible and irreversible degradation effects for PEMEL stacks in different operation modes. Our aim is to gain a better understanding of the variance of these phenomena in general and the recovery of reversible effects across PEMEL stacks. The measurements are carried out on a commercialized Greenlight E400 test bench equipped with a 7kW 8 cell PEMEL stack (Hydrogen Innovation GmbH). The potential of all cells will be monitored during testing. The measurements include repeated electrochemical characterization protocols measuring i/E-curves, HFR and impedance spectroscopy (EIS) of the PEMEL stack and if possible, every single cell. These protocols include the introduction of low potential regeneration phases before every characterization during the test protocol to distinguish between reversible effects and the irreversible cell degradation. This was seen to be effective for potential recovery by Suermann et al. 2019 for single PEMEL cells.4 The results consist of a description of the two testing procedures and the used equipment. Due to the duration of each test protocol (3000 h) only results of the static test protocol can be presented.The contribution of the presented research is threefold. Firstly, we break down the degradation across a whole stack. Giving valuable insights regarding the distribution of cell efficiency and degradation effects. Secondly, the presented test protocols characterize and account for the reversible rise in cell/stack potential. Thirdly, the characterization of the recovery time of the cell potential across the stack will have implications for the operation of stacks to mitigate or recover these performance losses. We address both static and dynamic operation modes aiming to simulate the application of PEMEL stacks for a constant production of hydrogen used in downstream processes and the volatile operation due to a direct coupling with renewable energy sources.This publication is to be seen as presentation of first results in our ongoing research to find test protocols for short stack systems to develop operation strategies, which can be applied to large scale electrolyzer systems. Furthermore, we try to deepen the understanding of the reversible cell potential rise as well as standardize the general testing of PEMEL stacks.This work is funded by the Federal Ministry of Education and Research (BMBF) in the project “hyBit” under the grant 03SF0687E. The authors declare that the opinions expressed in this submission are their own and are based on a thorough review of existing scientific literature. Sources 1. G. Tsotridis and A. Pilenga, EU harmonized protocols for testing of low temperature water electrolysis, Publications Office of the European Union, Luxembourg (2021). 2. A. Voronova, H.-J. Kim, J. H. Jang, H.-Y. Park and B. Seo, International Journal of Energy Research, 46 (2022) 11867. 3. C. Rakousky, U. Reimer, K. Wippermann, S. Kuhri, M. Carmo, W. Lueke and D. Stolten, Journal of Power Sources, 342 (2017) 38. 4. M. Suermann, B. Bensmann and R. Hanke-Rauschenbach, Journal of The Electrochemical Society, 166 (2019) F645-F652.

ПОРІВНЯННЯ РЕЗУЛЬТАТІВ МОДЕЛЮВАННЯ ЧАСТОТНО-РЕГУЛЬОВАНОГО АСИНХРОННОГО ЕЛЕКТРОПРИВОДУ

Abstract. The modelling of a frequency-controlled asynchronous electric drive was carried out using two software products Matlab and DIMASDrive. The consumed currents and active powers are determined both at the input of the drive and at the input of the asynchronous motor. The simulation results are compared with the results of experimental studies and the corresponding accuracy are found. Both static and dynamic modes of operation are considered. The advantages and disadvantages of the considered software products are established. The complementarity of these programs is substantiated, which makes it possible to use them together when performing certain tasks. Keywords: frequency-controlled asynchronous electric drive, Matlab program, DIMASDrive program, mathematical modelling, experimental studies, static modes, dynamic modes.

Design and Simulation of a Novel 16T SRAM Cell for Low Power Memory Architecture

Static random access memory (SRAM) is a sort of RAM where information is not permanently stored and does not require routine updating. To reduce leakage power without sacrificing performance, a variety of approaches have been applied to SRAM cells. In this study, we suggest a new 16T SRAM design that can function in active, park, standby, or hold modes. A fully static mode of operation for SRAM is made possible by the 16T SRAM structure, which also enhances write margin (WM) and removes charging conflict between devices during read and write operations. The key objectives of the suggested architecture are to retain logic state in park mode while maintaining stability and reducing standby time in active mode, as well as to reduce leakage current in standby mode. This is done by removing feedback from the back-to-back inverters during write operations via the data-dependent supply block. This makes it possible for the suggested bitcell to considerably increase the WM. A novel SRAM cell with 16 transistors is created with subthreshold operation and enhanced data stability. By using an equalized bit line technique to avoid leakage due to enhanced data pattern and RBL detection, the suggested single-ended SRAM cell with dynamic feedback control lowers the static noise margin for ultra-low power transfer. A sleep transistor is incorporated into the architecture to save power consumption when the system is in standby mode due to inefficient voltage transmission. Tanner EDA tool V.14.1 on 45-nm CMOS was used for design and simulation. The outcomes demonstrate a considerable decrease in no-load current and power loss.

Design, Development and Testing of a Monitoring System for the Study of Proton Exchange Fuel Cells and Stacks.

This article is about the design, development and validation of a new monitoring architecture for individual cells and stacks to facilitate the study of proton exchange fuel cells. The system consists of four main elements: input signals, signal processing boards, analogue-to-digital converters (ADCs) and a master terminal unit (MTU). The latter integrates a high-level graphic user interface (GUI) software developed by National Instruments LABVIEW, while the ADCs are based on three digital acquisition units (DAQs). Graphs showing the temperature, currents and voltages in individual cells as well as stacks are integrated for ease of reference. The system validation was carried out both in static and dynamic modes of operation using a Ballard Nexa 1.2 kW fuel cell fed by a hydrogen cylinder, with a Prodigit 32612 electronic load at the output. The system was able to measure the voltage distributions of individual cells, and temperatures at different equidistant points of the stack both with and without an external load, validating its use as an indispensable tool for the study and characterization of these systems.

TRANSITIONAL PROCESSES INVESTIGATION OF INDUCTION MOTOR STARTING WITH LAUNCH RHEOSTATS IN THE PHASE ROTOR CIRCLE

An induction motor electric drive (IM) is the most popular in industry and agriculture. This is result the ease of manufacture and operation, smaller than DC motors weight, dimensions, cost and reliability. Induction motors are divided into short-circuited (IMS) and with phase rotor (IMP). IMSs are characterized by high starting currents, torque and mainly operate in static mode. IMP has improved regulating properties, but they are characterized disadvantages as greater weight, dimensions and cost.
 In addition to the main static mode of operation, the IMS is often operated in transitional modes. Transitional modes occur when change shaft loading, power supply, circuit frequency, rotation direction when connected and disconnected from the network, when changing the parameters of the motor. The most difficult transitional modes are the processes of start-up, breaking, reverse and reconnection. There are current jumps in these modes and their duration depends on moment of inertia of all mechanism. Current jumps lead to the shocks of the drive, increased efforts in the windings of the stator and rotor. The electromagnetic torque in transitional modes has oscillation character with significant amplitudes, and the maximum rotor torque achieves five-time of nominal. Repeated and sometimes variable values of the electromagnetic torque IM in transitional modes cause accelerated wear of the mechanism, equipment and the motor.
 In mechanisms with repeated modes of operation (crane mechanisms etc.) IMP are widely used. In this case, additional start-up rheostats and contactors are required to limit current jumps and electromagnetic torque and as a result increase the smooth operation of the electric drive. Thus, the study of transitional processes in IMP in repeated modes is an actual task.

Synthesizing the Optimal Control of an Induction Motor-Based Traction Electric Drive with Taking into Account Magnetic Saturation and Core Losses

Traction electric drives based on an induction motor often employ vector control with orienting along the rotor flux vector, with which it becomes possible to achieve high performance indicators of the motor and drive as a whole in both static and dynamic operation modes. However, to achieve high energy efficiency of the drive, the use of optimal control strategies becomes of issue. This implies the need to set up, given a specified electromagnetic torque, the stator current flux-forming and torque-forming components according to a certain law to achieve the motor operation optimized with respect to the selected criterion. In the context of a traction electric drive, such criteria are stator current to be maximized or power losses to be minimized. In doing so, it is important to take into account the motor magnetic system saturation and core losses, which have a significant impact on the synthesis of optimal control strategies. The article gives the equations of electromagnetic processes in a cage induction motor with field-oriented control and with taking into account the above-mentioned specific features. A procedure for synthesizing optimal control strategies while minimizing power losses and stator current is also given. Differences in approaches to the synthesis of optimal strategies with and without taking the magnetic system saturation into account are shown.

Frequency control of asynchronous motor for an irrigation pump of machine irrigation systems

The working state of freguency-operated asinchronous motor of irrigation pump in the closed system with feedback by velocity are considered. The system issue coefficient, provided a constancy of given value, loading coefficient of motor for voltage control pro rata control freguency are determined. Let us consider the static mode of operation of a frequency-controlled AM in a closed system with speed feedback. A decrease in the rotation speed in irrigation pumps to regulate their productivity is possible up to a certain minimum value, at which the pump head (H) becomes equal to the static head (Hst). The pump output (Q) then drops to zero. The value “k” has been determined, which ensures the constancy of the AM overload factor over the entire range of control frequency change in a closed-loop frequency control system with feedback on the engine speed.

INVESTIGATION OF THE OPERATION MODES OF THE BELT-ROPE CONVEYOR ELECTROMECHANICAL SYSTEM WITH VECTOR-CONTROLLED INDUCTION ELECTRIC MOTORS

Continuous transport systems are the most promising type of movement of loose and artificial materials, have high productivity, technical and economic indicators and are widely used in world practice as main conveyors for the coal and mining industry. A special place in continuous transport is occupied by belt-rope conveyors, which are capable of transporting cargo over a distance of more than 30 km in one stop. As a rule, these main conveyors do not provide for the adjustment of movement parameters, the start is carried out using soft start systems. At the same time, such systems have high requirements for the parameters of dynamic modes of operation, the accuracy of working out the given movement program and the level of energy efficiency. The paper proposes a modern electric drive system using vector-controlled induction electric motors. The structure of the electromechanical system is given. A mathematical model of the electromechanical system was built using known methods. As part of the “MATLAB” Simulink application program package, a model for the investigation of dynamic modes of conveyor operation was obtained. On a specific example, a research of dynamic and static modes of conveyor operation with static load and the speed of movement variations of the traction element was carried out. Studies of the accuracy of working out the given law of motion showed that the maximum dynamic error in terms of speed and current is worked out in a time of up to 0.06 s. The maximum level of its amplitude does not exceed 0.33% of the constant speed of movement, which does not cause oscillatory processes in the conveyor and ensures stable operation of the electromechanical system. Investigation of the electromechanical system energy characteristics was conducted. Losses of active power do not exceed 12.5% of the consumed in the entire range of variation of the static load and speed of the traction element. Recommendations for the use of electromechanical systems with vector-controlled induction electric motors in belt-rope conveyors have been formulated.

Имитационное моделирование адаптивного идентификатора скорости асинхронного двигателя агломерационной машины

By means of simulation computer modeling, an effective variant of constructing an identifier for the speed of an asynchronous motor of an electromechanical system of a sintering machine is analyzed. The mathematical and algorithmic basis of the adaptive speed identifier (ASI) of an induction motor with a squirrel-cage rotor (ACIM) is given. Using the developed mathematical description of ASI with a reference model and using the apparatus of Lyapunov functions, an adequate computer simulation model was created. Compared with the existing methods for constructing identifiers in sensorless asynchronous electric drives, the proposed version of the ASI allows taking into account the discrete nature of the supply voltage of the ACIM at the output of the frequency converter with pulse-width modulation (PWM) of the output voltage and changing a larger number of equivalent circuit parameters. The stability of the speed identification process is provided in a wide range, sufficient to stabilize the speed of the trolleys according to the requirements of the technological process of sintering machines. As a result, the accuracy of speed identification in static and dynamic modes of operation of the electric drive increases. Simulation confirmed the operability of the proposed version of the identifier, proposed options for setting the AIS components. Universal, important for practical application results have been obtained, which allow both to build a high-precision system for identifying the ACIM speed in general and to refine the setting of the coefficients of the proposed version of the identifier in particular. An important property of the developed version of the ASI is its operability without loss of accuracy at near-zero and zero speeds of rotation and close to the nominal load torque on the ACIM shaft. In this regard, the practical application of the developed version, in addition to the drive of the sintering machine, is also possible in high- precision positioning systems for electric drives for various purposes.

Методика проектирования асинхронных гребных электродвигателей с заданным коэффициентом мощности

The article considers the problem of improving the quality of electricity, in particular the power factor. The increased value of the power factor leads to decreasing the reactive component of the currents in the ship power network and, as a result, to a decreased power of converting equipment, generators and cable products. There is studied 
 a section in the methodology of designing ship electrical machines developed at the Department of Electric Drives and Electrical Equipment of Coastal Power Plants in Admiral Makarov State University of Maritime and Inland Shipping, which allows to evaluate the parameters of asynchronous electric motors at the design stage. Today, in designing electrical machines there are used the methods developed in the last century, which do not allow to carry out electromagnetic calculations subject to the required value of the power factor. The power factor is known to be determined by empirical formulas after setting the main parameters of the mechanism. The equivalent circuit of asynchronous electric motor containing the parameters of stator and rotor windings, and its mathematical description based on equations corresponding to Kirchhoff's laws are considered. Transformations of the equations describing the electromagnetic processes in the engine given for the static mode of operation in a complex form are made. There are given the expressions that allow determining the magnetizing current, magnetic conductivities, magnetizing forces, air gap and magnetic saturation coefficients, overall dimensions of the electric motor, and electromagnetic torque that it develops. Basing on the transformed equations describing an asynchronous electric motor there have been derived the regularities that help set the value of the power factor as initial data at the stage of design. The practical significance of the applied methodology and importance of the chosen subject have been analyzed.

Pulsed transistor operation enables miniaturization of electrochemical aptamer-based sensors.

By simultaneously transducing and amplifying, transistors offer advantages over simpler, electrode-based transducers in electrochemical biosensors. However, transistor-based biosensors typically use static (i.e., DC) operation modes that are poorly suited for sensor architectures relying on the modulation of charge transfer kinetics to signal analyte binding. Thus motivated, here, we translate the AC "pulsed potential" approach typically used with electrochemical aptamer-based (EAB) sensors to an organic electrochemical transistor (OECT). Specifically, by applying a linearly sweeping square-wave potential to an aptamer-functionalized gate electrode, we produce current modulation across the transistor channel two orders of magnitude larger than seen for the equivalent, electrode-based biosensor. Unlike traditional EAB sensors, our aptamer-based OECT (AB-OECT) sensors critically maintain output current even with miniaturization. The pulsed transistor operation demonstrated here could be applied generally to sensors relying on kinetics-based signaling, expanding opportunities for noninvasive and high spatial resolution biosensing.

Имитационная модель силового трехфазного трансформатора бронестержневой конструкции с витым магнитопроводом

Background. One of the areas of industry digitalization is associated with the concept of digital twins, which allow simulating the operation of real devices in various modes. At present, simulation models of a three-phase rod-type transformer have been developed in the MatLab Simulink SimPowerSystem environment. The models can serve as the basis to design a digital twin of a real device. The problem is to find the most universal method for mathematical description of a transformer of unspecified design to develop its simulation model. The purpose of this study is to develop a simulation model of a three-phase shell-type transformer core with a twisted magnetic circuit and to study this model when the transformer is operating in steady and transient modes. Materials and methods. The authors have applied the methods to model electrical circuits based on the theory of ordinary differential equations, a simulation method using the MatLab Simulink SimPowerSystem software package. Results. The structural futures of the transformers with shell-core design and the main assumptions when developing the simulation model have been assessed. A system of nonlinear equations has been developed to find the flows and MMF generated by the windings of the device. A simulation model of a three-phase shell-core transformer with a twisted magnetic core has been developed. It is based on the obtained equations using the Algebraic Constraint block with the Solver function in MatLab Simulink SimPowerSystem. The results of simulation of dynamic processes in the transformer in various modes are presented. Conclusions. The results of the study can be used to design power transformers in engineering companies and under production conditions. It is also possible to use the developed models in case of power transformer operation to analyze the static and dynamic modes of operation of sections of electrical networks.

МОДЕЛЮВАННЯ СТАТИЧНИХ І ДИНАМІЧНИХ АВАРІЙНИХ РЕЖИМІВ ТА АНАЛІЗ СПОЖИВАННЯ ЕЛЕКТРИЧНОЇ ЕНЕРГІЇ ДІЛЬНИЧНОЇ ПІДЗЕМНОЇ ПІДСТАНЦІЇ ЗАЛІЗОРУДНОЇ ШАХТИ

Improve the existing model of power supply of the underground substation in static and dynamic modes of its operation and perform simulation of static and dynamic emergency modes of its operation.The paper is devoted to determining the possibility of modeling static and dynamic emergency modes of operation for a sectional underground substation operating in an iron ore mine. The model of two winding transformers in Matlab Simulink R2020b environment is proposed and justified. Computer simulation with the software Matlab Simulink R2020b allowed using more possibilities to calculate the power supply system of the sectional underground substation.The following methods were used to solve the problems: theoretical foundations of electrical engineering, electrical machines, power converter technology, mathematical analysis and computational mathematics.The use of the results of the work will provide opportunities for analysis of transient modes between static and dynamic (emergency) modes of operation of the power system of the iron ore mine, which in the future will reduce the cost of electricity consumed by the underground mine sub-station, as well as reduce the time and cost of finished electrical equipment to design new on the power system, and implement an intelligent power grid with controlled automated devices in real time.In the future, this will create new opportunities for conducting simulation to analyze transient modes between static and dynamic (emergency) modes of operation of the power system of the iron ore mine, which will further reduce the cost of electricity consumed by the site underground mine substation. This will reduce the time and cost of finished electrical equipment to design new loads on the power system, as well as to implement an intelligent electrical network with controllable automated devices in real time.

ВЫБОР ОПТИМАЛЬНОГО ПРОТИВОДЕЙСТВУЮЩЕГО УСИЛИЯ ДЛЯ ДОСТИЖЕНИЯ МАКСИМАЛЬНОГО БЫСТРОДЕЙСТВИЯ ЭЛЕКТРОМАГНИТА

Based on the analysis of switching devices and various electrical installations, the article shows that their main element is a high-speed electromagnetic device that performs the functions of a reacting organ and a drive. Both a polarized and a neutral electromagnet can be used as such a device. So far, polarized electromagnets have been most widely used as the fastest ones. However, there are a number of designs of neutral type electromagnets that can replace polarized electromagnets, in particular in electric locomotive circuit breakers. An analysis of the state of the problem showed that the methods for calculating and studying high-speed electromagnetic devices require more rigorous and accurate mathematical calculations that allow replacing experimental studies in real emergency conditions and at the same time automating the work of researchers through the widespread use of more accurate calculations. The results of theoretical studies of processes occurring in high-speed electromagnets, mathematical dependencies for calculating parameters and characteristics, both in static and dynamic modes of operation, are presented. An equation was obtained to determine the optimal counteracting force, at which the cycle time is minimal. Mathematical algorithms have been developed for calculating the static and dynamic characteristics of high-speed electromagnets, taking into account steel saturation, leakage fluxes, eddy currents in massive elements of magnetic circuits and current conductors.

Static and dynamic instability modeling of electro-magneto-active polymers with various entanglements and crosslinks

Electro-magneto-active (EMA) polymers-based smart actuators suffer from electro-magneto-mechanical instability (EMMI) phenomena arising due to the positive feedback between the applied electric and magnetic fields and reduction in the polymer thickness. This work presents a theoretical investigation of EMMI phenomena of an EMA polymeric actuator in both static and DC dynamic modes of operation. A physics-based non-affine material model is adopted here for capturing the effect of the polymer chain entanglements and crosslinks on the instability phenomena. Simultaneously, a computationally efficient energy approach for obtaining the DC dynamic instability parameters is constructed, which depends on the energy balance at the position of maximal overshoot in an oscillation cycle. The findings from the current study illustrate the trends of variation in the deformation, electric field, and magnetic field at the onset of static and dynamic EMMI with the polymeric entanglements and crosslinks parameters. It is observed that large entanglements and crosslinks in polymer chains improve the stable operation travel range, which positively impacts the actuator performance.

Anti-Bacterial Action of Plasma Multi-Jets in the Context of Chronic Wound Healing

This work is a contribution to the development and implementation of non-thermal plasma technology for decontamination in the perspective of nosocomial and chronic wound innovative therapies. Multi jets devices based on Plasma Gun® technology in static and scanning operation modes and bacterial lawns inoculated with resistant and non-resistant bacterial strains were designed and used. A pilot toxicity study exploring plasma treatment of wound bearing patients, performed with a low voltage plasma applicator, is documented as a first step for the translation of in vitro experiments to clinical care. Bacterial inactivation was demonstrated for Staphylococcus aureus, Pseudomonas aeruginosa and drug resistant S. aureus, P. aeruginosa and Escherichia Coli strains collected from patient wounds at Orleans (France) hospital. A few square centimeter large contaminated samples were inactivated following a single plasma exposure as short as one minute. Samples inoculated with a single but also a mix of three resistant pathogens were successfully inactivated not only right after their contamination but for mature lawns as well. Similar bactericidal action was demonstrated for antibiotic-resistant and non-resistant P. aeruginosa. The time exposure dependent increase of the inhibition spots, following multi jets exposure, is discussed as either the accumulation of reactive species or the likely combinatory action of both the reactive species and transient electric field delivery on inoculated samples.

Removal of emerging contaminants (bisphenol A and antibiotics) from kitchen wastewater by alkali-modified biochar

Using current wastewater treatment technologies, it can be challenging to remove the emerging contaminants (ECs) present in kitchen wastewater (KW) of complex compositions and high organic content. In this study, biochar, derived from straw, was modified as an adsorbent to remove ECs such as bisphenol A (BPA), tetracycline (TC) and ofloxacin (OFL) from a complex KW system. An alkali-modified biochar, having larger specific surface areas and stronger hydrophobicity, was found to exhibit a higher adsorption capacity, with more than 95% of the target ECs being removed. Indeed, in a static operation mode, the alkali-modified biochar had maximum adsorption capacities of 71.43, 101.01 and 54.05 mg/g for BPA, TC, and OFL, respectively. The adsorption kinetics and isotherms models indicated that the adsorption process was controlled by chemisorption, as well as the monolayer adsorption of contaminants onto the external and internal surfaces of the alkali-modified biochar. The adsorption of TC and OFL was significantly affected by the initial pH values of KW. However, the presence of different environmental factors (COD, NH4+ and PO43−) had little effects on the adsorption of the contaminants. The alkali-modified biochar was further tested in a fixed-bed column where the maximum dynamic adsorption capacities for BPA and OFL were 55 and 45 mg/g, representing about 75% and 83% of the static saturated adsorption capacities. These findings can be of major significance for the application of alkali-modified biochar in the removal of ECs from complex KW systems.

Development of model of transient modes taking into account mutual inductance of scattering fields for implementation of digital twin of transformer

Development of the refined mathematical models of power transformers (digital twins), which make it possible to calculate arbitrary modes of operation of these devices with high accuracy and increased speed is an urgent task. Currently, such problems are solved using simulation packages such as MatLab Simulink. One of the disadvantages of the existing simulation models of the transformer is the assumption that own leakage inductance of the windings is used. This assumption is not always acceptable. Thus, the purpose of this article is to develop models of transformers using matrices of mutual inductance of the scattering field. The finite element method is used to calculate the magnetic field in a 2D formulation, implemented by means of the EMLib library, as well as simulation methods with the MatLab Simulink package are applied. The authors have estimated the features and basic assumptions while developing refined mathematical models of power transformers of various designs (two- and three-winding). It makes possible to ensure the required accuracy when simulating transient and emergency modes of transformer operation. Field models have been developed to determine the own and mutual scattering inductance matrices. Simulation models of transformers of various designs with the use of winding leakage inductance matrices have been developed. The results of simulation of dynamic processes in a transformer in various modes are presented. Comparison of the results of the operation of models with matrices of mutual inductances and without them is carried out. The results of the research can be used during the design of power transformers in design companies and in production environment. It is also possible to use the developed models during operation of power transformers for the analysis of static and dynamic modes of operation of sections of electrical networks.

On the potential of ROI imaging in x-ray CT - A comparison of novel dynamic beam attenuators with current technology.

In this work, we explore the potential of region-of-interest (ROI) imaging in x-ray computed tomography (CT). Using two dynamic beam attenuator (DBA) concepts for fluence field modulation (FFM) previously developed, we investigate and evaluate the potential dose savings in comparison with current FFM technology. ROI imaging is a special application of FFM where the bulk of x-ray radiation is propagated toward a certain anatomical target (ROI), specified by the imaging task, while the surrounding tissue is spared from radiation. We introduce a criterion suitable to quantitatively describe the balance between image quality inside an ROI and total radiation dose with respect to a given ROI imaging task. It accounts for the mean image variance at the ROI and the effective patient dose calculated from Monte Carlosimulations. The criterion is further used to compile task-specific DBA trajectories determining the primary x-ray fluence, and eventually used for comparing different FFM techniques, namely the sheet-based dynamic beam attenuator(sbDBA), the z-aligned sbDBA(z-sbDBA), and an adjustable static operation mode of the z-sbDBA. Furthermore, two static bowtie filters and the influence of tube current modulation (TCM) are included in the comparison. Our findings demonstrate by simulations that the presented trajectory optimization method determines reasonable DBA trajectories. The influence of TCM is strongly depending on the imaging task. The narrow bowtie filter allows for dose reductions of about 10% compared to the regular bowtie filter in the considered ROI imaging tasks. The DBAs are shown to realize substantially larger dose reductions. In our cardiac imaging scenario, the DBAs can reduce the effective dose by about 30% (z-sbDBA) or 60% (sbDBA). We can further verify that the noise characteristics are not adversely affected by the DBAs. Our research demonstrates that ROI imaging using the presented DBA concepts is a promising technique toward a more patient- and task-specific CT imaging requiring lower radiation dose. Both the sbDBA and the z-sbDBA are potential technical solutions for realizing ROI imaging in x-ray CT.