Circuit Modes Research Articles

Research of Parameters of Electric Power Systems Affecting Core Saturation of Current Transformers with a Closed Magnetic Circuit in Transitional Short Circuit Modes

The relevance of the study is due to the excess of the permissible errors of current transformers in transient short-circuit modes associated with saturation of the cores of current transformers. The latter leads to improper operation of relay protection devices, which can negatively affect the stability of electric power systems and the efficiency of industrial enterprises with a continuous technological cycle, the power failure of which leads to significant economic damage. The aim of this work is to study the parameters of electric power systems that affect the saturation of the cores of current transformers with a closed magnetic circuit in transient short-circuit modes. The object of research is electromagnetic current transformers of accuracy class 10P in electric power systems. The study was carried out using numerical methods for solving algebraic and differential equations, methods of computer modeling of electromagnetic transient processes and functional programming. As a result, the main parameters influencing the nature and intensity of electromagnetic transients in current transformers during a short circuit are noted; it is shown that in transient short-circuit modes, significant errors in the operation of current transformers associated with core saturation are possible; recommended for assessing the compliance of current transformers of accuracy classes 5P, 10P with the conditions for the correct functioning of relay protection devices in transient short-circuit modes, to calculate the time to saturation of current transformers, taking into account the real parameters of the electric power system at the place where current transformers are installed, in addition to the traditional design checking of current transformers by permissible er-rors for the steady state short circuit.

Analysis of Symmetric Dual Switch Converter under High Switching Frequency Conditions

Electric vehicle batteries have the problem of low output voltage, so the application of a high-gain converter is a research hotspot. The symmetrical dual-switch high gain converter has the merits of simple structure, low voltage and current stress, and low EMI. Due to the deterioration of circuit performance caused by circuit parasitic parameters under high frequency operating conditions, the former analysis under low frequency condition cannot satisfy the requirements for performance evaluation. To clarify whether the symmetrical dual-switch high-gain converter can maintain its operating characteristics under high-frequency operating conditions, this paper establishes the converter model considering parasitic parameters, and deduces the sneak circuit modes at high frequency. The effects of parasitic parameters at high frequency on voltage gain, switch stress, and symmetrical operating are analyzed, which is beneficial for the selection and optimization of power devices. This paper believes that considering parasitic parameters may reduce the output gain of the symmetrical double-switch high-gain converter considering parasitic parameters under high frequency conditions, increase the switching stress, and affect the symmetry of the circuit operation when the parasitic parameter values are different. Finally, an experimental platform rated on 200 W with 200 kHz switching frequency is established, and experimental verification is given to verify the analysis.

MODELING OFDISTRIBUTION TRANSFORMERS BY A 3-D NUMERICAL TECHNIQUE

Modeling of electromagnetic quantities (magnetic flux, leakage flux, eddy current loss, and electromagnetic force) in distributed power transformers remarkably plays an essential role for researchers and designers in the calculation and production of electrical equipment in general and transformer designs in particular. In the frame of this research, the distribution of magnetic flux densities along the tank wall and cover plate, the leakage flux in air regions, and the forces for both rated and short circuit modes in the windings of the transformer are computed/simulated via a 3-D numerical method. The method is herein developed with magnetic vector potential formulations and is applied to a practical application of the distributed transformer (630kVA-22/0,4kV).

Topological edge states of interacting photon pairs emulated in a topolectrical circuit

Topological physics opens up a plethora of exciting phenomena allowing to engineer disorder-robust unidirectional flows of light. Recent advances in topological protection of electromagnetic waves suggest that even richer functionalities can be achieved by realizing topological states of quantum light. This area, however, remains largely uncharted due to the number of experimental challenges. Here, we take an alternative route and design a classical structure based on topolectrical circuits which serves as a simulator of a quantum-optical one-dimensional system featuring the topological state of two photons induced by the effective photon-photon interaction. Employing the correspondence between the eigenstates of the original problem and circuit modes, we use the designed simulator to extract the frequencies of bulk and edge two-photon bound states and evaluate the topological invariant directly from the measurements. Furthermore, we perform a reconstruction of the two-photon probability distribution for the topological state associated with one of the circuit eigenmodes.

Thermal modelling of oil-filled power transformer TM - 160/10

The results of modeling the thermal characteristics of the dry and oil-filled power transformer TM-160/10 in idle and short circuit modes are presented. The electrical, geometric and thermal characteristics of the TM-160/10 transformer are determined. Computer modeling is performed in the software package ANSYS 17.1. The 2D distributions of temperature and density of heat flows in the transformer in the longitudinal and transverse sections are determined. It is shown that the use of transformer oil for cooling the transformer significantly reduces the temperatures in the active part. The temperature distribution occupies the range of 67-91 °С. Accordingly, the temperature of the most heated part is 91 °C and also corresponds to the low voltage winding. The dependence of the most heated point of the transformer on the operating mode was studied. A formula is proposed for calculating the maximum temperature of a transformer as a function of power loss.

A proposed single-stage single-phase full bridge boost inverter

ABSTRACTA proposed topology for a high-efficiency single-stage single-Phase boost inverter with a simple circuit configuration and a low component count is proposed in this paper. The proposed inverter produces instantaneous output voltages higher than the input dc voltage without an intermediate power conversion stage. A new control scheme is designed that enables the proposed inverter topology to produce a low distortion sinusoidal output waveforms and provide good load voltage regulation. The inverter circuit topology and modes of operations are fully described and simulated using Matlab/Simulink. The simulation results are presented illustrating the claimed boosting characteristics, sinusoidal output wave forms and good load regulation capability of the proposed inverter. The validity and effectiveness of the proposed inverter are verified experimentally by building a laboratory model using the digital signal processor (Model DS1104). The experimental results are presented confirming the claimed features of the inverter.

Soft-Switching Bidirectional DC/DC Converter With an LCLC Resonant Circuit

In this paper, a soft-switching bidirectional dc/dc converter with an LCLC resonant circuit is proposed. The proposed converter has the dual advantages of isolated converter and nonisolated converter. In boost mode, high efficiency can be achieved at high boost ratios. In buck mode, the circuit can also achieve automatic voltage equalization of half-bridge capacitors. In this paper, a detailed theoretical analysis of the LCLC structure is performed, and the specific operating modes of the circuit in buck and boost mode are given. The circuit modes of the soft-switching resonant process are quantitatively analyzed. The GSSA method was used to model and control the system. According to the obtained transfer function, the PID control circuit of the system is designed by using the zero-pole cancelation method, which enabled the system to obtain superior control performance. A prototype of 1000 W was made, and the experimental results are in a good agreement with the theoretical results.

OPTIMAL PLACEMENT OF PIEZOELECTRIC ELEMENT ON A PLATE INTERACTING WITH A FLUID LAYER

In this paper, we determine the optimal location of the piezoelectric element on the upper surface of a plate, interacting with a layer of a quiescent fluid of finite size. As a quantity, allowing us to evaluate the operating efficiency of a piezoelectric element in damping a single specified mode of structure vibrations, we take the electromechanical coupling coefficient. It is calculated based on the values of the natural frequencies of the system, obtained for the two characteristic performance modes of an electric circuit (open and short circuit modes). The behavior of the piezoelectric element is described by the equations of electrodynamics of deformable electroelastic media in the framework of the quasi-static approximation. The motion of an ideal fluid in the case of small perturbations is considered in the framework of the acoustic approximation. Small strains in a thin plate are determined using the Reissner – Mindlin theory. The numerical implementation of the problem is carried out using the finite element method. The obtained results made it possible to identify situations, where the optimal location of the piezoelectric element can be determined without considering the effect of the fluid.

Distance backup protection using supply currents on a line with several branches

The third step of distance protection is used as backup protection against phase-to-phase short circuits on 110–220 kV transmission lines. The main problem when using these protections on a line with several branches is to ensure the effectiveness of distant backup protection in case of phase-to-phase short circuits behind branch transformers of substations. The effective solution to distant backup protection is possible to provide by expanding the information base of protection. Currently, backup protection of lines with branches is being developed with control of currents and their components when using a communication channel, and based on algorithmic models of the facility. In this regard, the urgent task is to develop an algorithm for the distance protection ensuring the required sensibility during short circuits on the lower voltage side of the branch transformers. Analytical methods of determining the impedance measurement and simulation in Simulink and SimPowerSystems of the Matlab modeling system are used. The effectiveness of distant backup protection can be evaluated on the basis of recognition possibility of short circuit modes behind the branch transformers. Analytical expressions have been obtained to determine the impedance measurement during phase-to-phase short-circuits behind a branch transformer and under load conditions. Criteria have been developed to assess the proposed protection possibility to recognize the mode of phase-to-phase short circuits behind the branch transformer. Studies have shown that the main factor determining the possibility of mode recognition is the ratio between the protected transformer power and the total power of the branches loads. The use of several impedance measuring elements with their own response characteristics for branches with transformers of different capacities provides mode recognition for any possible correlation of power of branch substations. The use of the distance protection implementation option developed by the authors allows providing the required sensitivity for short circuits behind branch transformers and to solve the problem of distance backup line protection on a line with several branches. The reliability of the data obtained is confirmed by the correspondence of analytical research and simulation results.

Forced Commutated Controlled Series Capacitor Rectifier for More Electric Aircraft

Rising power demands in more electrical aircraft (MEA) put power converters for commercial airplanes under increasing pressure to fulfill current harmonic distortion regulations as specified, for example, in DO-160G. Today, the implementation of filters is seen as an effective tool for dealing with harmonics; however, their increased weight and volume are not welcomed in the aerospace industry. This paper proposes a circuit, named forced commutation controlled series capacitor (FCSC-rectifier), which is able to maintain low individual harmonic current levels without the need for filter components. The FCSC-rectifier includes a variable capacitive line reactance that interacts in a controlled manner with the inductive line impedance. The result is that the converter input current is nearly purely sinusoidal with a power factor of almost unity. The FCSC-rectifier is to be used for stand-alone variable-voltage, variable-frequency generation systems and can, therefore, power the full authority digital electronic control system (FADEC) in an MEA. This paper shows that the FCSC-rectifier can maintain a high power factor and acceptable current harmonic levels without the use of filters, despite large voltage and frequency variations. A full description of the circuit modes of operation is presented in this paper together with simulation results showing circuit performance characteristics over a range of voltages and frequencies. Results are experimentally verified using a 1-kW test circuit.

СИНХРОНИЗАЦИЯ ВЕКТОРОВ ТОКОВ И НАПРЯЖЕНИЙ ПРИ ОПРЕДЕЛЕНИИ МЕСТА ПОВРЕЖДЕНИЯ НА ВОЗДУШНЫХ ЛИНИЯХ ЭЛЕКТРОПЕРЕДАЧИ

The article presents and analyzes the method of current and voltage phasors synchronization in the end points of the overhead power line when detecting fault location in order to test the efficiency of the method. Short circuit modes in the overhead transmission line are simulated using the Matlab software. The methods of fault localization in the overhead power line based on measuring the values of emergency condition parameters are applied. An algorithm implementing the proposed method of fault localization by synchronizing current and voltage phasors in the end points of the overhead power line is developed. The algorithm and the method have been tested. A series of short circuits is performed on the simulation model in the different points of the line in order to get the values of current and voltage phasors and use them for the two-end localization of the fault using the proposed method of phasor synchronization. The inaccuracy of the two-end localization of the fault resulting from asynchronized nature of current and voltage phasors reaches the highest values under short circuits in the end points of the line. It is attributable to the highest phase angle between the measured phasors of current and voltage. The maximum inaccuracy of the given model of the overhead power line is 4.5% at the phase angle of 23 degrees. The studies based on the mathematical model of the overhead power line have proved that the use of the introduced method of current and voltage phasor synchronization significantly increases the accuracy of fault localization in the overhead power lines while the error caused by asynchronized measurements is reduced to zero.

A High-Efficiency CMOS Rectifier with Wide Harvesting Range and Wide Band Based on MPPT Technique for Low-Power IoT System Applications

This paper describes a wide-harvesting-range, wide band, and high-efficiency complementary metal-oxide-semiconductor (CMOS) rectifier for low-power application in internet of things systems. Through maximum power point tracking, the proposed rectifier can dynamically detect the output voltage to enable switching between various circuit modes in order to achieve higher power conversion efficiency (PCE), even during sub-1-V operation. The experimental results for a $$0.18\hbox {-}\upmu \hbox {m}$$0.18-μm standard CMOS process with a 1.8-V power supply voltage demonstrate that the proposed rectifier can operate from a low voltage (0.7 V) to a high voltage (1.8 V) while maintaining high PCE. The proposed rectifier achieves a PCE improvement of 16% from the rectifier with a bootstrapping circuit under a peak alternating current (AC) input voltage of 0.85 V, and of 47.5% from the fully cross-coupled rectifier under a 1.8-V peak AC input voltage. Moreover, because its structure is insensitivity to the frequency response, the proposed rectifier provides a wide operating frequency range of 10---960 MHz.

Sampling for silver nanoparticles in aqueous media using a rotating disk electrode: evidence for selective sampling of silver nanoparticles in the presence of ionic silver.

Amendment of a carbon paste electrode consisting of graphite and Nujol®, with a variety of organic and inorganic materials, allows direct adsorption of silver nanoparticles (AgNPs) from aqueous solution in either open or close circuit modes. The adsorbed AgNPs are detected by stripping voltammetry. Detection limits of less than 1ppb Ag are achievable with a rotating disk system. More than one silver peak was apparent in many of the stripping voltammograms. The appearance of multiple peaks could be due to different species of silver formed upon stripping or variation in the state of aggregation or size of nanoparticles. With most of these packing materials, dissolved Ag+ was also extracted from aqueous solution, but, with a packing material made with Fe(II,III) oxide nanoparticles, only AgNPs were extracted. Therefore, it is the best candidate for determination of metallic AgNPs in aqueous environmental samples without interference from Ag+.

Напряжения, наводимые на грозозащитном тросе воздушной линии электропередачи, как фактор риска. Часть 2

To ensure the personnel safety during live working on overhead transmission line (OTL), as well as lightning protection
 cables’ (LPC) isolation integrity maintaining, by the example of three-phase 750 kV OTL has been presented an algorithm
 for calculation of voltages, electro-moving forces and currents induced by single phase short-circuit currents’ magnetic field
 of OTL in LPC1 grounded in one point, and in LPC 2 (with fiber-optic communication line function) grounded at every tower.
 For single-phase short circuit modes has been presented an algorithm for length selection of grounded on one end LPC1
 part on the condition of compliance with the maximum permissible voltage level on a spark gap which bypasses an
 insulator set of LPC1.

Recent progresses in bus-ducts design

Purpose – Electrical energy distribution systems must be low losses systems in order to enhance the system efficiency. Therefore, it is preferred to distribute electrical energy by bus-ducts in the place of cables over all energy levels and decrease the losses. The purpose of this paper is to focus on a comprehensive survey of various aspects of bus-ducts design including electromagnetic, mechanical and thermal. Advantages and disadvantages of different available design techniques are reviewed. Design/methodology/approach – Different works on various bus-based power transmission and distribution systems are reviewed. Generally these are done in three categories including systems modeling methods, heat transfer in the systems, short circuit and electromagnetic force. The attempt is made to provide geometrical and materials specifications in order to present the analyzed system well. Findings – Different types of bus-ducts from used materials, voltage level and insulation types are reviewed. Bus-duct modeling techniques are introduced which can be easily applied for bus-ducts design. Electromagnetic field distribution, thermal pattern inside and outside of the bus-duct in normal and short circuit modes and finally mechanical considerations are dominant factors which must be taken into account in the bus-ducts design. This leads to an optimal design of bus-ducts which prolong the life span of the bus-ducts fixed in the installations. Originality/value – This paper for the first time systematically reviews the latest state of arts in the design of bus-ducts for efficient electrical energy distribution. It summarizes a variety of design techniques applicable to bus-ducts design.

Algorithm and Software for Operative Calculations of the Short Circuits Modes

Smart power grids provide efficient control of power flows or other grid variables, such as voltages or short circuit currents. Most essential the control has become, if the consumers are electrical systems of high power capacity. These systems are able to reconfigure the grid structure for emergency situations. The developed algorithm is intended for carrying out operational calculations of short-circuits modes in electrical grids of voltage 0,4kV to 220kV. In the calculation the following methods have been used: methods of node voltages, method of superposition and method of branch expansion to form the node voltage matrix according to the graphs theory. In the software the short circuit inflow from all electrical motors and nodes with generalized load is taken into account as opposed to other algorithms. The calculated circuit can have up to 700 nodes; there is ability to decrease number of branches and nodes and to form the calculative model of the grid part. Calculation algorithm of the short circuit currents is implemented as a sequence of software calculations. Software of systems and grids, in which short circuits are altered, allows carrying out operational calculations of the short circuit modes to adjust settings of relays protection devices, to check electrical equipment and to replace it, to choose optimal operational circuits. Actuality of the calculations is caused by need of the software implementation to maintain, upgrade and design the electrical grids of enterprises that have their own power plants.

Evaluation and enhanced operational performance of microbial fuel cells under alternating anodic open circuit and closed circuit modes with different substrates

The present study evaluates the performance of air-cathode microbial fuel cells (MFCs) under alternating open circuit/closed circuit (OC/CC) modes and its effect on independent-electrode and full-cell potentials, power output (at different external resistances) and the polarization behaviour of the electrodes. Three different types of feeds were evaluated using this approach: (1) phosphorus buffer solution (PBS) with acetate as carbon source, (2) glucose-rich synthetic wastewater, and (3) sewage from wastewater treatment plant enriched with fermented molasses. When MFCs were suddenly switched to CC from OC and then again back to OC from CC, the behaviour of the anodes vs reference electrode (Ag/AgCl, 3M KCl) was monitored. When electric circuit of the MFCs was switched from open to closed circuit, for all cases: (a) the anode potential-shift (vs Ag/AgCl) reallocated in the positive direction in about 200–400mV, (b) the air-cathode potential-shift (vs Ag/AgCl) reallocated in the negative direction in about 10–25mV, and (c) the cell-potential difference started at around 0mV and progressively increased as the MFC reached stability. This behaviour was consistently reproduced during different OC/CC cycles. The systems studied delivered good performance with both controlled media and industrial wastewater. Additionally, this study provides insightful characterization of the independent-electrode behaviours.

Ageing of DSSC studied by electroluminescence and transmission imaging

Outdoor stability testing of ionic liquid based dye sensitised solar cells under short circuit (SC) and open circuit (OC) modes has been followed using electroluminescence (EL) and transmission imaging. The study showed a significant influence of the ageing conditions on the stability of the solar cell parameters in the exposure period from zero up to 31kWh/m2 (four summer days) of solar irradiation. Initial exposure is beneficial for all performance parameters regardless the operating mode under which the cells were aged. After 8kWh/m2 ageing of the cells in SC mode downgrades all parameters, mainly Jsc and consequently η, while continues ageing in OC mode slightly increases Voc and consequently η. The EL imaging demonstrated that ageing, regardless the operating mode, is associated with the growth of the EL inactive areas that appear as black spots or defects, which we associate with the formation of iodine species in the electrolyte that have been captured under confocal microscope. The stability testing demonstrates that growth of the defects is more pronounced for cells operated in SC mode, which primarily reduces stability of Jsc.

ANALYSIS OF HARMONIC COMPOSITION OF THE ALTERNATING MAGNETIC FIELD ASSOCIATED WITH THE ROTATING ROTOR OF TURBOGENERATOR IN THE NO-LOAD AND SHORT-CIRCUITS MODES

The method of calculation of the magnetic field alternating component at the surface of the rotating rotor of turbo generator is presented. It is based on multiposition of the numerical calculations of the magnetic field with the rotor turns and changes of currents in the stator winding. Discrete time functions of the alternating component of the magnetic induction are selected in points of the surface . The harmonic analysis is conducted for them. The developed method is universal in terms of excitation modes, designs and the magnetic core saturation. The theory is confirmed by computational researches in the no-load and short circuit modes of large turbo generator. In it, the alternating component of the magnetic induction on the rotor surface in the short-circuit mode is much greater than in the no-load mode. Values and harmonic composition of the alternating component of the magnetic induction differ substantially at different points of the rotor surface. Harmonics are ponderable in the range from the level determined by the phase structure of stator winding to the level determined by the tooth structure of its core. The results obtained are qualitatively fit into the classical notion of oscillatory processes of the magnetic field on the rotor surface, but now the value and harmonic composition of the alternating component of the magnetic induction receive adequate numerical filling. The result of work can be used for designing of a turbogenerators and other synchronous machines.

The investigation of reverse traction current influence on tone track circuit modes

Introduction: With the introduction of high-speed traffic there is an increased consumption of traction current by new types of rolling stock. This issue is important, as high levels of traction currents can have not only prevents, but also a dangerous impact on the equipment of railway automation devices. It is necessary to investigate the propagation of traction currents and potentials along the rails. Objective: Investigate the propagation of traction currents and potentials along the rails, the determination of critical currents, which not executed tone track circuits modes. Methods: In order to investigate the mathematical model, and the method of calculation tone track circuits modes was used. Results: By means of mathematical model, which includes being several rolling-stocks at the feeder zone, different rail resistance and isolation, the diagrams of currents and potentials propagations for DC and AC electric traction have been obtained. A comparative analysis of the experimental data and the results of the investigation has been realized. Based on received levels of reverse traction current their influence on track circuit modes has been investigated. Conclusions: The reverse traction current level near the substation and rolling-stock can be more than 600A. Great reverse traction current levels have an influence on tonal track circuit functioning, namely normal and shunt modes. When the traction current arrives 200 A there is a reduction criteria of tonal track circuits.