Detection of voltage sag sources based on the angle and norm changes in the instantaneous current vector written in Clarke’s components

The presented research reflects those methods for detecting voltage sag sources that only use measurements of line currents. It is shown that the phasor-based method known from the literature is unsatisfactory, especially in the cases of transient voltage sag events. Therefore, a generalised method is proposed that is based on the instantaneous current vector written in Clarke’s components. The phasor-based method and the proposed method for voltage sag source detection were evaluated by applying extensive simulations, laboratory tests, and field testing. The obtained results show considerably higher effectiveness for the proposed method. The correctness of the instantaneous vector-based approach is verified in this way. Moreover, the proposed method that uses only measurements of line currents is just as effective as some other instantaneous vector-based methods that use measurements of line currents and line voltages.     

The current state and possibilities for development of switchgears for a voltage of 6–35 kV

General trends in the development of electrical-distribution systems and requirements for switchgears (SGs) for midrange voltage are considered. The main advantages of conventional SGs with air insulation are indicated. Problems of transitioning to SGs with solid insulation and solid shielded insulation are considered. The volume of cells with air insulation is from three to five times greater than that of present-day SG cells with solid insulation and gas-filled cells. It is determined that application of SISS (Solid Insulated Switchgear with an grounded Shield) technology shows the greatest promise for improving SGs with solid insulation. The solid shielded insulation extends the equipment’s service life before possible repair, thus decreasing the maintenance expenses. Various manufacturers’ schematic structural variations of manufacturing of cells with solid insulation are described. The main engineering solutions of the offered designs are presented. Their advantages and disadvantageous features have been indicated. Application of the proposed system allows one to reduce the size of SGs and significantly increase security, as contacts with high-voltage are not used in a compartment SG. In addition, the moving elements of SGs under high potential require another insulation medium that will allow these elements to move, e.g., a gas, liquid, or vacuum. This means that insulation of such SG in principle is combined. Moreover, the solid insulation layer worsens heat dissipation. High electrostatic-field strengths in solid dielectric and large volumes of molded solid dielectric require special means to eliminate partial discharges. Interconnection of various elements presents a serious problem, and the elements’ boundary surface is the most weakened insulation node. For this reason, application of such elements requires elaborate engineering and special engineering solutions that improve insulation’s performance reliability and improve thermal conditions.     

Dynamic response analysis and output voltage control of asymmetric half bridge DC–DC converter for low voltage applications

Asymmetric control scheme is an approach to achieve Zero Voltage Switching (ZVS) for half bridge isolated DC–DC converters. Due to the switching property included in their structure, DC–DC converters have a nonlinear behavior and their controller design is accompanied with complexities. But by employing the average method it is possible to approximate the system into a linear system and then linear control methods can be used. Dynamic performance of half bridge converters output voltage can be controlled by Pole placement and PID controllers. In this paper, Genetic Algorithm is used to optimize the system to achieve the optimum dynamic response. Matrix coefficients and dominant poles of closed loop transfer function is selected based on Genetic Algorithm. The results show an improvement in voltage control response in a short time.     

Determination of phase angle and amplitude error of voltage and current transformers up to some 100 Hz for loss measurements on power transformers

Contents  For the load loss measurement of power transformers, current and voltage transformers with usually extremely low errors of phase angle and amplitude are used. However, even small errors of the measuring transformers may result in an error in the measured load loss. Therefore, national and international standards allow the correction of the measured value by the amount caused by phase angle and amplitude error of the measuring equipment [2–4]. The determination of the errors of phase angle and amplitude of measuring transformers is carried out on the basis of calibrated standard measuring transformers which are traceable to national standard equipment at rated frequency, e.g. at 50 and 60 Hz. For some applications – e.g. the load loss measurement of HVDC power transformers according to the draft of IEC standard 61378-2 [1] – a load loss measurement at frequencies other than rated frequency is required. For that, the errors of phase angle and amplitude of the measuring transformers must be known. This paper describes a method how to determine the phase angle and amplitude errors of the measuring transformers at arbitrary frequencies on the basis of the calibrated error values at rated frequency. Received: 9 August 2000     

Comparison of calculated and measured I–V curves for DNA

Cohen et al. have reported experimental observations of current passing through the dsDNA molecules using a metal-covered atomic force microscope (AFM) tip; the molecules are chemically connected to a metal substrate at one end and to a gold nanoparticle (GNP) at the opposite end. They have presented evidence for charge transport through dsDNA molecules of a complex sequence, 26 bp long, characterized by S-shaped current–voltage (I–V) curves. In this paper, theoretical calculations giving excellent agreement with the results of Cohen et al. are obtained using the formalism of Datta et al.     

Application of a system with distributed architecture for information acquisition and processing in tasks of active–adaptive voltage control in distribution electric grids

An active–adaptive control system for power grids with distributed architecture of data acquisition and processing is considered. The advantages of the proposed control principle are compared with commonly used methods. A domestic apparatus—a programmable recording bay controller (PRBC)—is described. This hardware was designed to measure the basic electrical parameters and create distributed systems for data acquisition and processing. The procedure is considered of supervisory control and data acquisition (SCADA) by the SONATA system based on a multicore distributed architecture having high reliability and supporting a rigid real-time mode. A full-function full-scale model of active–adaptive voltage control system (AAVC) was set up using proposed software and hardware. The AAVC makes it possible to use the results of calculating–measuring procedures to select a corresponding on-load tap-changer (OLTC) on the actual voltage levels in the nodes of distribution grid. This approach to centralized voltage control in distribution grids makes it possible to ensure the required level of voltage in the greatest possible number of power consumers owing to prediction of voltage change. The effect of emergencies (random failure of control equipment) during the operation of an active–adaptive voltage control system is analyzed. A qualitative evaluation of the effect of faults on regulation quality and choice of OLTC connection is carried out. It is shown that, for undisturbed operation of an active–adaptive voltage control system, additional diagnostic tools, backup, and data loss compensation are needed.     

A robust SMES controller strategy for mitigating power and voltage fluctuations of grid-connected hybrid PV–wind generation systems

Electrical Engineering - Recently, hybrid generation systems (HGSs) are considered to be the optimal solution for supplying remote areas with the required electrical power. HGSs contain two or more...     

Quality monitoring of electrical power to evaluate the operational reliability of power equipment and active–adaptive voltage control in distribution power grids

Monitoring systems of power quality and operation mode parameters are currently being developed and widely introduced. These systems make it possible to receive needed information in different nodes of a grid in real time, as well as build up data archives over a long period of time. The presence of such information makes it possible to change the approach to short- and long-term control by distribution grids. This paper describes the possibilities of application of information obtained from a monitoring system to control distribution power grids using the example of reliability evaluation of power equipment to schedule the repairs, and active–adaptive voltage control system. The dependences are shown of probability of failure of power equipment on operation time under different types of load curves and power quality. The conclusion is drawn that the wear of main equipment significantly increases when it is operated in conditions of low power quality. The dependence is shown of changing repair and inspection frequency of equipment on operation time and operating conditions. This paper describes the structure and principles of operation of an active–adaptive voltage control system. As a test example, the amount of violations upon steady-state voltage deviations of power consumers in a distributed grid using different methods of voltage control in a power supply center are compared. It is shown that, at nonuniform load in the grid, the required voltage level cannot be provided by the counterload regulation method. The ease of use of a monitoring system of the power quality of operation mode parameters of power consumers makes it possible to use the control system providing a required voltage level for the greatest number of power consumers.     

Modeling and Management of Batteries and Ultracapacitors for Renewable Energy Support in Electric Power Systems–An Overview

Abstract—Energy storage devices and systems are playing a major role in all electrical systems from small electronics devices and automotive systems to the utility grid. The main objective of this article is to review energy storage devices, management, control, interface, and demonstrations for electrical power systems. Various types of energy storage systems are discussed, but the main focus is on batteries and ultracapacitors. Different types of batteries and their electrical models are explained. Three major types of ultracapcitors are also discussed. The battery management system and its functions, controls, and hardware are discussed. Various power electronics-based interface systems for battery and ultracapcitor charging and discharging are presented. Applications of energy storage systems for utility applications, including renewable firming, power shifting, and ancillary services, are discussed.     

Efficient design and simulation of an expandable hybrid (wind–photovoltaic) power system with MPPT and inverter input voltage regulation features in compliance with electric grid requirements

In this paper an efficient design along with modeling and simulation of a transformer-less small-scale centralized DC—bus Grid Connected Hybrid (Wind–PV) power system for supplying electric power to a single phase of a three phase low voltage (LV) strong distribution grid are proposed and presented. The main components of the hybrid system are: a PV generator (PVG); and an array of horizontal-axis, fixed-pitch, small-size, variable-speed wind turbines (WTs) with direct-driven permanent magnet synchronous generator (PMSG) having an embedded uncontrolled bridge rectifier. An overview of the basic theory of such systems along with their modeling and simulation via Simulink/MATLAB software package are presented. An intelligent control method is applied to the proposed configuration to simultaneously achieve three desired goals: to extract maximum power from each hybrid power system component (PVG and WTs); to guarantee DC voltage regulation/stabilization at the input of the inverter; to transfer the total produced electric power to the electric grid, while fulfilling all necessary interconnection requirements. Finally, a practical case study is conducted for the purpose of fully evaluating a possible installation in a city site of Xanthi/Greece, and the practical results of the simulations are presented.     

Series and parallel resistance effects on the C–V and G–V characteristics of $$\mathrm{Al}/\mathrm{SiO}_{2}$$/Si structure

This paper investigates the electrical behavior of the C–V and G–V characteristics of \(\mathrm{Al}/\mathrm{SiO}_{2}/\mathrm{Si}\) structure. The modeling of capacitance and conductance has been developed from complex admittance treatment applied to the proposed equivalent circuit. Poisson transport equations have been used to determine the charge density, surface potential, total capacitance, and flatband and threshold voltages as a function of the gate voltage, frequency (\(\omega )\), and series \(({R}_{\mathrm{s}})\) and parallel \(({R}_{\mathrm{p}})\) resistances. Results showed a frequency dispersion of C–V and G–V curves in both accumulation and inversion regimes. With increasing frequency, the accumulation capacitance is decreased, whereas the conductance is strongly increased. The shape, dispersion, and degradation of C–V and G–V characteristics are more influenced when parallel and series resistances \((\mathrm{R}_{\mathrm{s}}\), \(\mathrm{R}_{\mathrm{p}})\) are dependent to substrate doping density. The variation of \(\mathrm{R}_{\mathrm{s}}\) and \(\mathrm{R}_{\mathrm{p}}\) values led to a reduction of flatband voltage from ?1.40 to ?1.26 V and increase of the threshold voltage negatively from ?0.28 to ?0.74 V. A good agreement has been observed between simulated and measured C–V and G–V curves obtained at high frequency.     

Investigation of the BaTiO3–BaMg1/3Nb2/3O3 system: Structural, dielectric, ferroelectric and electromechanical studies

Lead-free (1?x) BaTiO₃ –x BaMg_1/3Nb_2/3O₃ ceramics with x?=?0.03, 0.04, 0.05 and 0.06 were prepared by solid-state synthesis. The effects of the Ba(Mg_1/3Nb_2/3)O₃ addition on the phase composition, dielectric and ferroelectric properties, as well as the electromechanical response of the classic ferroelectric BaTiO₃ were investigated. The room-temperature X-ray diffraction analyses of all the ceramics revealed a perovskite phase after sintering at 1300 °C with a composition-dependent symmetry. The samples with a lower concentration of Ba(Mg_1/3Nb_2/3)O₃, i.e., x?=?0.03 and 0.04, were tetragonal, while the samples with x?=?0.05 and 0.06 were found to be cubic. The result is in agreement with the dielectric, ferroelectric and electromechanical properties. With x increasing from 0.03 to 0.06 the temperature of the diffused maximum of the dielectric permittivity decreased from 348 K to 265 K. All the ceramics showed a large electromechanical response: the calculated room-temperature electrostrictive coefficient M ₃₃ of the sample with x?=?0.06 was 1.4 · 10^?16?m²/V², which is comparable to the value measured for Pb(Mg_1/3Nb_2/3)O₃ ceramics.     

Simple and efficient estimation of I–V photovoltaic using nonlinear curve fitting equivalent circuit model in Lambert W function form

Journal of Computational Electronics - A new and simple computational technique to estimate efficiently and extract key parameters of PV cells and modules are proposed using experimental...     

The PT-30/35–8.8/1.0-5M and PT-40/50–8.8/1.0 steam turbines for replacing turbines of the VPT-25 family

The basic design features and technical characteristics of the turbines installed on the foundation of turbines of the VPT-25 family are presented.     

Assessment of MRF for simultaneous T1 and T2 quantification and water–fat separation in the liver at 0.55 T

Magnetic Resonance Materials in Physics, Biology and Medicine - The goal of this work was to assess the feasibility of performing MRF in the liver on a 0.55 T scanner and to examine the...     

On the storage batteries used in solar electric power systems and development of an algorithm for determining their ampere–hour capacity

Storage batteries are indispensable in all stand alone solar electric systems (PV power systems). Their efficiencies and life times affect significantly the overall PV system performance and economics. Batteries specified especially for use in PV systems have to be distinguished with standing of very deep discharge rate and high cycling stability.Ordinary batteries being marketed world wide for use in automobile, are mostly not appropriate for PV power systems. The most important characteristics of lead–acid batteries are presented and discussed in this paper. Moreover, the paper illustrates an experimental procedure for developing an algorithm for determining the ampere–hour capacity of batteries operating in PV systems. This algorithm enables determining the state-of-charge of a battery by measuring voltage and electrolyte-specific gravity at definite temperature and is applicable also for large battery storage systems.