Electric Current System Research Articles

Offshore wind farm layout optimization using mathematical programming techniques

Offshore wind power is a renewable energy of growing relevance in current electric energy systems, presenting favorable wind conditions in comparison with the sites on land. However, the higher energy yield has to compensate the increment in installation and maintenance costs, thus the importance of optimizing resources. One relevant aspect to increase profitability is the wind farm layout. The aim of this paper is to propose a new method to maximize the expected power production of offshore wind farms by setting the appropriate layout, i.e. minimizing the wake effects. The method uses a sequential procedure for global optimization consisting of two steps: i) an heuristic method to set an initial random layout configuration, and ii) the use of nonlinear mathematical programming techniques for local optimization, which use the random layout as an initial solution. The method takes full advantage of the most up-to-date mathematical programming techniques while performing a global optimization approach, which can be easily parallelized. The performance of the proposed procedure is tested using the German offshore wind farm Alpha Ventus, located in the North Sea, yielding an increment of expected annual power production of 3.52% with respect to the actual configuration. According to current electricity prices in Germany, this constitutes an expected profit increment of almost 1 M€ per year.

Location of Large-Scale Concentrating Solar Power Plants in Northeast Brazil

Heliothermic electricity generation is gaining popularity in several countries worldwide. In Brazil, this form of energy generation has not yet been explored for large scale projects. However, the country possesses extensive areas with normal and high-intensity direct irradiation and low seasonality factors, particularly in the semi-arid region of the Brazilian Northeast. The region also presents other important features for setting up such plants: proximity to transmission lines, sufficient flatness, non-endangered vegetation, a suitable land use profile low maximum wind speeds, low population density, and more recently, an increase in the demand for local electric energy due to economic growth above the Brazilian average. A Geographic Information System includes a set of specialised resources that allow us to manipulate spatial data, providing quickness and efficiency in the identification of appropriate places for installing solar power plants while also preparing us for future scenarios, with regards to their impacts, costs and benefits. This article presents a study of the optimal location for thermoelectric power plants in the semi-arid region of the Brazilian Northeast on the scale of 1:10,000,000. All provinces with good potential for the implementation of large-scale concentrating solar power plants are identified. Considering that the installed capacity for parabolic cylindrical concentrators in terrains with a steepness of less than 1% is 43.26 MW/km2 for systems without storage and 30.82 MW/km2 for systems with 6 hours of storage, the potential of the southeast region of Piaui alone is huge. Even with the lack of information about the urban areas, terrain continuity, and other variables,utilising only 10% of the identified potential area, or879.7 km2, would result in an installed capacity of 38.1-27.1 GW. This value corresponds to more than 1/3 of the potency of the current Brazilian electric system. If the same calculation is made for the semi-arid region of the Brazilian Northeast, its capacity will be greater than 1000 GW.

The Analysis in Several Application Issues for Leakage Current Electrical Fire Monitoring System

This paper starts with an introduction into the current situation of electical fires and the development of electrical fire monitoring systems. Then the paper summarizes some main issues of leakage current electric fire monitor system of engineering application. In order to improve product quality, the necessity of carrying out some tests is dicussed in this paper, too, such as the product feature extension, EMC tests, super-current shock test, balance test and the transformer function test. Nest, the paper proposes some ideas on the standardization of electric fire prevention and the improvement of management policy. Finally, a few suggestions for the sound development of electric fire prevention application are provided.

Analysis of Smart Grid with 132⁄33 KV Sub-Transmission Line In Rural Power System of Bangladesh

“Smart Grid” is a modern concept which refers to the conversion of the mainstream or typical electric power grid to a modern power grid. This new conversion is a foreseeable solution to the power system problems of the modern century. Rejuvenation of the current electric power distribution system is an important step to implement the Smart Grid technology. So, distribution system engineers should be acquainted with the knowledge of Smart Distribution System. Also the customers should acknowledge the benefits that they will be enjoying from this modernized power system. There are power crisis everywhere in the world, besides there is system loss in the existing power system. It is happening in Bangladesh also. To reduce power crisis renewable source of energy like solar energy, wind energy, raw coal energy may be used. But the quantity of electricity produced by this renewable energy source is low and several kilowatts range. This electricity is utilized by smart grid which is hard for usual power grid system. For this reason we need hybrid ac/dc smart control grid system. In this report models using Wind-mil Software is proposed for reducing system loss and also incorporate smart metering so that the power flow can reach easily to the consumers. Smart grid also helps sole proprietor and individual business man to sell their little amount of electricity to the grid which they produce by their own entrepreneurship through smart meter. Line loss and regulated voltage, regulator and capacitor are also inserted here to reduce the loss and make the effective and efficient power supply to the consumer. This metering is also centrally controlled and works over a huge area. At present developing country should develop this system.

Effect of R2‐FAC development on the ionospheric electric field pattern deduced by a global ionospheric potential solver

Toward the understanding of the effect of the magnetosphere originated disturbances on the global ionospheric electric field and current system, we developed a two‐dimensional ionospheric potential solver based on the so‐called “thin shell model.” The important extension from the previous studies is that our model covers the pole‐to‐pole ionosphere without placing any boundary at the equator. By using this solver, we investigate how the ionospheric electric field changes from undershielding condition to overshielding condition as the field aligned current (FAC) distribution changes. Calculations are performed by changing IR2/IR1 (the ratio of current intensities of region 2 (R2) and region 1 (R1) FACs) and by moving R2‐FAC relative to the fixed R1‐FAC. The results are summarized as follows: (1) The turning point, at which the ionosphere turns from undershielding to overshielding is IR2/IR1 = 0.7 ∼ 0.8. (2) With increasing the local time deference between the R1 and R2‐FAC peaks, the efficiency of the shielding by R2‐FAC increases but the associated potential skews to the nightside. (3) At the same time the shielding effect is weakened around noon, where the R1‐potential intrudes to the low latitude region instead, but the R2‐potential remains dominant at other local times. The result suggests that the overshielding or undershielding should be identified by observations not only in a limited local time sector but also in the overall ionosphere as much as possible. In order to accurately describe the ionospheric condition, we suggest new classification terms, “complete‐overshielding” and “incomplete‐overshielding.”

Generating resilience: exploring the contribution of the small power producer and very small power producer programs to the resilience of Thailand's power sector

“Resilience thinking” is an increasingly popular approach among scholars and policymakers, with advocates heralding it as the successor to the dominant sustainable development paradigm. Resilience refers to the ability to handle unforeseen changes and the capacity for adaption and self-improvement as a result. This article examines two programs for renewable, distributed power generation in Thailand from a resilience perspective. The research contributes to the existing literature by applying the resilience concept to electricity generation and governance in the Thai power sector. The case is interesting because of the vulnerability of Thailand's current electricity system and the fact that the programs are prototypical among developing nations. A conceptual model is constructed from the literature and used to analyze the programs based on information from expert interviews and other sources. Results suggest that the programs are increasing the resilience of the system, but their contribution is limited by barriers related to governance.

Increased Aerobic Fitness After Neuromuscular Electrical Stimulation Training in Adults With Spinal Cord Injury

Carty A, McCormack K, Coughlan GF, Crowe L, Caulfield B. Increased aerobic fitness after neuromuscular electrical stimulation training in adults with spinal cord injury. ObjectivesTo evaluate the efficacy of a novel neuromuscular electrical stimulation (NMES) system for improving aerobic fitness in individuals with spinal cord injury (SCI). It was hypothesized that training with this NMES system would increase peak oxygen consumption (Vo2peak) and peak heart rate (HRpeak) in a sedentary adult SCI population. DesignProspective cohort study. SettingAll testing took place at a university human performance laboratory. ParticipantsVolunteer participants with SCI (N=16; T4-11 American Spinal Injury Association Impairment Scale grades A and B) were recruited from the national SCI outpatient and outreach service databases. All completed the training program, but results from 2 participants were excluded because posttraining tests were invalid. Therefore, 14 participants (11 men, 3 women) completed the program and testing. InterventionsFour electrodes (175cm2) were placed bilaterally on the quadriceps and hamstrings muscle groups, and subtetanic contractions were elicited using an NMES device. Training was undertaken unsupervised at home for 1 hour, 5d/wk for 8 weeks. Main Outcome MeasuresAn incremental treadmill wheelchair propulsion exercise test with simultaneous cardiopulmonary gas exchange analysis was used to determine Vo2peak and HRpeak. ResultsA statistically significant increase in Vo2peak (P=.001) and HRpeak (P=.032) between baseline and follow-up was observed. ConclusionsThis novel form of NMES is an effective method of improving aerobic fitness in an SCI population. Results are comparable to those with current functional electrical stimulation exercise systems.

MAGNETOSPHERES OF “HOT JUPITERS”: THE IMPORTANCE OF MAGNETODISKS IN SHAPING A MAGNETOSPHERIC OBSTACLE

Weak intrinsic magnetic dipole moments of tidally locked close-in giant exoplanets ( hot Jupiters ) have been shown in previous studies to be unable to provide an efficient magnetospheric protection for their expanding upper atmospheres against the stellar plasma flow, which should lead to significant non-thermal atmosphere mass loss. The present work provides a more complete view of the magnetosphere structure of hot Jupiters, based on a paraboloid magnetospheric model (PMM). Besides the intrinsic planetary magnetic dipole, the PMM considers among the main magnetic field sources also the electric current system of the magnetotail, magnetopause currents, and the ring current of a magnetodisk. Due to the outflow of ionized particles from the hydrodynamically expanding upper atmosphere, hot Jupiters may have extended magnetodisks. The magnetic field produced by magnetodisk ring currents dominates above the contribution of an intrinsic magnetic dipole of a hot Jupiter and finally determines the size and shape of the whole magnetosphere. A slower-than-the-dipole-type decrease of the magnetic field with the distance forms the essential specifics of magnetodisk-dominated magnetospheres of hot Jupiters. This results in their 40%–70% larger scales compared to those traditionally estimated by only the planetary dipole taken into account. Therefore, the formation of magnetodisks has to be included in the studies of the stellar wind plasma interaction with close-in exoplanets, as well as magnetospheric protection for planetary atmospheres against non-thermal escape due to erosion by the stellar plasma flow. Key words: planets and satellites: magnetic fields – planets and satellites: physical evolution – planets and satellites: rings – planet–star interactions

Chemical Preparation and Characterizationof Polypyrrole-Polylactic Acid Conductive Composite Membranes

Abstract: Conductive polypyrrole(PPy)-polylactic Acid(PLA) composite membranes are prepared with chemical method. Membranes have been characterized by Fouier transform infrared spectroscopic(FT-IR) and scanning electron microscopy （SEM).The conductive stability of membranes has been measured by home-made multiwell direct current electrical stimulating system. The results show PPy nanparticals network embeds in PLA matrix and the conductive stability of membranes sustains in the range of 28μA~35μA between the observation time of 560h to 1146h.

How to fit demand side management (DSM) into current Chinese electricity system reform?

DSM is one of the best and most practical policy tools available to China for balancing environmental protection and economic growth. The new round of electricity system reform provides a good opportunity to consolidate and integrate DSM policy and expedite its development and implementation. DSM policy can be upgraded by incorporating it into the current electricity system reform. Comparing the potential acceleration of electricity price reform with the possibility of imposing a System Benefit Charge (SBC), the author argues that support for a SBC would be much easier to gather among policymakers and stakeholders in a short time and would have a much better policy effect in the current situation. The author discusses three kinds of price discrimination related to the DSM development in China: time-based electricity pricing, electricity price discrimination for industrial structure adjustment in China (Fujian Province as a case), and direct power purchases by large customers and preferential tariff policy. These can be well designed to be combined with DSM and energy efficiency policy.

Magnetic coupling of planets and small bodies with a pulsar wind

We investigate the electromagnetic interaction of a relativistic stellar wind with a planet or a smaller body in orbit around the star. This may be relevant to objects orbiting a pulsar, such as PSR B1257+12 and PSR B1620-26 that are expected to hold a planetary system, or to pulsars with suspected asteroids or comets. We extend the theory of Alfv\'en wings to relativistic winds. When the wind is relativistic albeit slower than the total Alfv\'en speed, a system of electric currents carried by a stationary Alfv\'enic structure is driven by the planet or by its surroundings. For an Earth-like planet around a "standard" one second pulsar, the associated current can reach the same magnitude as the Goldreich-Julian current that powers the pulsar's magnetosphere.

Spanish microgrids: current problems and future solutions

Some years ago microgrids (μ-grids) became the most promising solution to the problems of the current electric system. There are many studies that demonstrate the advantages of using μ-grids, among which the following can be highlighted: microgrids can improve power quality inside and outside them; supply reliability of the internal loads is higher [1][2]; and the generalization of μ-grids could extend the usage of distributed generation (DG) systems. Despite being very extended in the scientific and engineering world, the μ-grid concept is not usual in the ordinary world. Proof of this is that current electric legislation does not include their usage. Prior to its spread, μ-grids must have an appropriate legal and economic environment. Through this text, the authors would like to show the legal limitations that the μ-grids usage will find in Spain and the solutions that are applied in other countries and states. The final objective of this paper is to present a legal and economic framework that would promote the development of μgrids in Spain.

Interpolation of externally-caused magnetic fields over large sparse arrays using Spherical Elementary Current Systems

Abstract. A physically-based technique for interpolating external magnetic field disturbances across large spatial areas can be achieved with the Spherical Elementary Current System (SECS) method using data from ground-based magnetic observatories. The SECS method represents complex electrical current systems as a simple set of equivalent currents placed at a specific height in the ionosphere. The magnetic field recorded at observatories can be used to invert for the electrical currents, which can subsequently be employed to interpolate or extrapolate the magnetic field across a large area. We show that, in addition to the ionospheric currents, inverting for induced subsurface current systems can result in strong improvements to the estimate of the interpolated magnetic field. We investigate the application of the SECS method at mid- to high geomagnetic latitudes using a series of observatory networks to test the performance of the external field interpolation over large distances. We demonstrate that relatively few observatories are required to produce an estimate that is better than either assuming no external field change or interpolation using latitudinal weighting of data from two other observatories.

Valuing diversity in energy supply

There is renewed interest in the role of supply diversity in promoting energy security. This paper explores ways of valuing diversity. A possible incentive mechanism for promoting diversity which takes account of underlying “disparities” between different technology options is developed. The mechanism provides a way of trading off cost and diversity and results in an “efficient” cost-diversity frontier by analogy with financial portfolio theory. If all technologies are believed to be equally disparate, the appropriate mechanism is a “levy” imposed on market share. If the technologies are not equally disparate, the levy needs to be adjusted by technology-specific multipliers that take account of levels of disparity and patterns of market share. The analysis is applied to two stylised situations. In the long-run equilibrium case, the implications of both different patterns of disparity and different values attached to diversity are investigated. The paper also explores the implications of applying such a mechanism to the current Great Britain electricity system. The implications in terms of financial flows, for both the market as a whole and for individual operators, are investigated. Finally, the appropriateness of such a mechanism in the light of other policy goals, and possible future research directions, is discussed.

A methodology to generate statistically dependent wind speed scenarios

Wind power – a renewable energy source increasingly attractive from an economic viewpoint – constitutes an electricity production alternative of growing relevance in current electric energy systems. However, wind power is an intermittent source that cannot be dispatched at the will of the producer. Modeling wind power production requires characterizing wind speed at the sites where the wind farms are located. The wind speed at a particular location can be described through a stochastic process that is spatially correlated with the stochastic processes describing wind speeds at other locations. This paper provides a methodology to characterize the stochastic processes pertaining to wind speed at different geographical locations via scenarios. Each one of these scenarios embodies time dependencies and is spatially dependent of the scenarios describing other wind stochastic processes. The scenarios generated by the proposed methodology are intended to be used within stochastic programming decision models to make informed decisions pertaining to wind power production. The methodology proposed is accurate in reproducing wind speed historical series as well as computationally efficient. A comprehensive case study is used to illustrate the capabilities of the proposed methodology. Appropriate conclusions are finally drawn.

Online fuzzy voltage collapse risk quantification

Many voltage stability indicators have been proposed in the past for the voltage collapse assessment. Almost all of them are determined through quite complex analytical tools; therefore, it is difficult for system operators to give them a physical meaning. In order to perform a simple and reliable evaluation of the security margins, it is necessary to make a synthesis of the information given by the various indices. The present work proposes an Artificial Intelligence-based tool for the evaluation of the voltage security. In particular, a Fuzzy Inference Engine is developed and optimized by two different approaches (Neural Networks and Genetic Algorithms). Starting from the state estimation, a given set of mathematical indices is computed to represent a snapshot of the current electric system operating point. The numerical values are then translated into a set of symbolic and linguistic quantities that are manipulated through a set of logical connectives and Inference Methods provided by the mathematical logic. As a result, the Fuzzy Logic gives a MW measure of the distance from the collapse limit, a metric usually appreciated by system operators. The Fuzzy System has been built and optimized by using, as a test system, a detailed model of the EHV Italian transmission network connected to an equivalent of the UCTE network (about 1700 buses).

Historical variation of the geomagnetic axial dipole

The geomagnetic axial dipole (hereinafter denoted g 1 0 ) is the largest component of our planet’s magnetic field. Its magnitude determines the morphology of solar-terrestrial electrical current systems and it is the most fundamental diagnostic property of the core-generated geodynamo. Elucidating past and future variations of g 1 0 ( t ) is consequently of central importance in geomagnetism. Previous historical geomagnetic field models, such as gufm1 of Jackson et al. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Philos. Trans. R. Soc. Lond. A 358, 957–990], used direct observations to constrain g 1 0 ( t ) only after 1840 A.D.; before this time a crude linear extrapolation of the post-1840 A.D. rate of change (15 nT/year) was employed. In this contribution I construct historical field models with g 1 0 ( t ) instead constrained from 1590 A.D. to 1840 A.D. by an archaeointensity dataset compiled by Korte et al. [Korte, M., Genevey, A., Constable, C.G., Frank, U., Schnepp, E., 2005. Continuous geomagnetic field models for the past 7 millennia. 1. A new global data compilation. Geochem. Geophys. Geosyst. 6, doi:10.1029/2004GC000800]. A range of possible linear models of the form g 1 0 ( t ) = g 1 0 ( 1840 ) + β ( t − 1840 ) are first explored; β = 2.74 ± 42.32 nT/year is found to explain the archaeointensity dataset with maximum likelihood, consistent with the recent findings of Gubbins et al. [Gubbins, D., Jones, A.L., Finlay, C.C., 2006. Fall in Earth’s magnetic field is erratic. Science 312, 900–902]. Relaxing the linear constraint in an effort to find more physically plausible models, I find it is necessary to artificially increase the weight given to the archaeointensity data in order to obtain acceptable models. Despite satisfactorily explaining both the historical and archaeointensity data, and possessing reasonable spatial and temporal complexity, such free evolution models perform worse than the simpler linearly constrained models when tested against the independent dataset of Gallet et al. [Gallet, Y., Genevey, A., Fluteau, F., 2005. Does Earth’s magnetic field secular variation control centennial climate change? Earth Plan. Sci. Lett. 236, 159–173]. Bayesian model comparison techniques indicate that a model ( gufm1-g10c) involving no change in g 1 0 ( t ) between 1590 A.D. and 1840 A.D. is most probable given the presently available data and current modelling techniques. I propose that this new, empirically derived, constraint on the evolution of the geomagnetic axial dipole be incorporated into the next generation of historical field models.

Natural radioactivity, earthquakes, and the ionosphere

Air ionization produced by natural ground radioactivity, mainly by radon emanating from the Earth's crust, is a primary source of ions in the planetary boundary layer (PBL) of the atmosphere over land [Hoppel et al., 1986]. These ions provide the air conductivity responsible for fair weather vertical electric current in the global electric circuit (GEC), a system of stationary electric currents between the ground and ionosphere driven by global thunderstorm activity. This activity is considered an electric generator of the potential difference between the ground and ionosphere (200–600 kilovolts), and the return downward current closes the circuit in the areas of fair weather [Roble and Tzur, 1986]. The upper closing limit of this circuit is of the altitude of 60 kilometers. At altitudes higher than 60 kilometers, cosmic rays and solar radiation also contribute to air ionization.

Galactic cosmic rays

In this brief review we describe the theory of the origin of Galactic cosmic rays. The concept that interaction near the source is the dominant source of γ-rays, and spallation secondaries seems best suited to explain the EGRET γ-spectrum of the inner Galaxy, the abundances of light elements, the anti-protons and the positrons. Also the chemical abundances seem best described as resulting from the chemical composition of massive star winds. This leads to a supernova mechanism, long known, that the magneto-rotational mechanism provides the energy, about 1052 erg, for the explosion of the most massive stars; this mechanism naturally allows to understand jet-supernovae and Gamma Ray Bursts from its underlying symmetry. A key theoretical question remains open: the role of magnetic fields, both in the transport of cosmic rays in the Galaxy, as well as in the enhancement they may get in shock waves on various length scales, either starting with existing magnetic fields, or starting from electric current systems. An ultimate hope and expectation obviously is, once we understand the origin and physics of cosmic rays, to turn them into a tool to understand to understand the nature of matter at a yet deeper level.

Numerical modelling of the Earth’s magnetosheath for different IMF orientations

A new magnetosheath numerical MHD model has been developed which calculates solar wind flow around a paraboloidal obstacle. Steady-state solutions have been obtained for different interplanetary magnetic field orientations, namely for the strictly northward and southward interplanetary magnetic fields, and for the case of a large B x component. It has been found that the magnetic field magnitude and values of other MHD parameters in the magnetosheath depend on the direction of the interplanetary magnetic field. Particularly, the magnetic field near the magnetopause is weaker for the southward interplanetary magnetic field than for the northward interplanetary magnetic field due to the magnetopause reconnection, and the magnetic barrier may almost disappear for a special interplanetary magnetic field orientation nearly aligned with the solar wind velocity. Three electric current systems are simulated in this work: the currents at the bow shock, in the magnetosheath, and on the magnetopause.