This paper evaluates an electronic current transformer’s wideband accuracy in the transformation of distorted current harmonics. The tests were performed in the range of frequencies from 50 Hz to 5 kHz. The utmost importance was dedicated to the transformation of the low-order higher harmonics. The novelty of this paper involves the analysis of the self-generation of the third and fifth higher harmonics caused by the nonlinearity of magnetic core magnetization characteristics. Therefore, what is considered new in this investigation is that this phenomenon has a significant influence on values of current errors and phase displacements despite the presence of the operational amplifiers and the Hall sensors in the output circuits. Another important factor to consider is the influence of the RMS value of the primary current and output load of the ECT on wideband accuracy. To show the backgrounds of the performed laboratory studies, we also discuss the operation principles of the ECTs with... [more]

Promoting the development of green technologies and replacing fossil fuel vehicles with electric ones can abate the environmental anxieties and issues associated with energy supply security. The increasing demand for electric vehicles requires an upgrade and expansion of the available charging infrastructure to accommodate the fast public adoption of this type of transportation. Ethiopia set a pro-electric cars policy and made them excise-free even before the first electric vehicle charging stations were launched by Marathon Motors Engineering in 2021. This paper presents the first ever technical, economic and environmental evaluation of electric vehicle charging stations powered by hybrid intermittent generation systems in three cities in Ethiopia. This paper tests this model using three different battery types: Lead-acid (LA), Flow-Zince-Bromine (ZnBr) and Lithium-ion (LI), used individually. Using these three battery technologies, the proposed hybrid systems are then compared in ter... [more]

The growing energy demand has increased the consumption of hydrocarbons in developing countries such as Mexico, which has contributed to accelerating global warming. Although Mexico has suitable offshore wind energy harvesting sites, technical assessments to identify technologies to be placed in specific locations are scarce. In Mexico, offshore wind resources are found in depths larger than 50 m. There, floating platforms are convenient for harnessing wind energy. This work presents a technical evaluation of offshore wind energy in one of the regions with a higher availability of wind resources on the Mexican coasts, the Tehuantepec Gulf, in the Pacific Ocean. First, a specific location is chosen to evaluate its maritime conditions and theoretical wind energy potential. Next, the performance of a floating offshore wind turbine platform has been investigated numerically using potential flow simulations. The motions of the platform were analyzed for different drafts when subjected to di... [more]

Alkali metal compounds are released during the thermal conversion of biofuels and fossil fuels and have a major impact on the efficiency of conversion processes. Herein, we describe a novel method for the simultaneous characterization of alkali release and mass loss from materials used in combustion and gasification processes including solid fuels, fluidized bed materials, and catalysts for gas reforming. The method combines the thermogravimetric analysis of selected samples with the on-line measurement of alkali release using a surface ionization detector. The technique builds on the careful treatment of alkali processes during transport from a sample to the downstream alkali monitor including the losses of alkali in the molecular form to hot walls, the formation of nanometer-sized alkali-containing particles during the cooling of exhaust gases, aerosol particle growth, and diffusion losses in sampling tubes. The performance of the setup was demonstrated using biomass samples and flui... [more]

In recent years, demand for electric energy has steadily increased; therefore, the integration of renewable energy sources (RES) at a large scale into power systems is a major concern. Wind and solar energy are among the most widely used alternative sources of energy. However, there is intense variability both in solar irradiation and even more in windspeed, which causes solar and wind power generation to fluctuate highly. As a result, the penetration of RES technologies into electricity networks is a difficult task. Therefore, more accurate solar irradiation and windspeed one-day-ahead forecasting is crucial for safe and reliable operation of electrical systems, the management of RES power plants, and the supply of high-quality electric power at the lowest possible cost. Clouds’ influence on solar irradiation forecasting, data categorization per month for successive years due to the similarity of patterns of solar irradiation per month during the year, and relative seasonal similarity... [more]

A smart grid is an intelligent power grid. In recent years, the smart grid environment and its applications are incorporated into a variety of areas. The smart grid environment, however, can expose much more information than the old environments. In the environment, smart devices can be media in the exposure of various and specific pieces of information as well as energy consumption. This poses a huge risk in that it, combined with other pieces of information, may expose much more information. The current smart grid environment raises a need to develop anonymous signature and authentication techniques to prevent privacy breaches. Trying to meet this need, the principal investigator conducted research for three years. This paper discusses both the research trends investigated by him and the limitations of the development research and future research in need. Smart grid security requires the development of encrypted anonymous authentication that is applicable to power plant security, inc... [more]

The present paper reports on the numerical simulation of flow dynamics in a model gas-turbine combustor by large eddy simulation in order to evaluate the effect of coherent flow structures on the local fluctuations of gas temperature and local concentrations of NO and CO. The simulations were performed for a generic swirler, based on the design by Turbomeca, for a Reynolds number of 15,000 at normal and elevated inlet temperature and pressure (up to 500 K and 3.4 atm). The simulation data were validated based on the velocity measurements by stereoscopic particle image velocimetry. In order to reveal coherent flow structures, the velocity snapshots were processed by the proper orthogonal method. The temporal coefficients of the decomposition were used to evaluate the conditional sampled spatial distributions of the temperature and species concentration. It is shown that the coherent fluctuations of temperature can locally reach up to 200 K with the fluctuations of NO up to 20%. Thus, th... [more]

The growing penetration of renewable resources such as wind and solar into the electric power grid through power electronic inverters is challenging grid protection. Due to the advanced inverter control algorithms, the inverter-based resources present fault responses different from conventional generators, which can fundamentally affect the way that the power grid is protected. This paper studied solar inverter dynamics focused on negative-sequence quantities during the restoration period following a grid disturbance by using a real-time digital simulator. It was found that solar inverters can act as negative-sequence sources to inject negative-sequence currents into the grid during the restoration period. The negative-sequence current can be affected by different operating conditions such as the number of inverters in service, grid strength, and grid fault types. Such negative-sequence responses can adversely impact the performance of protection schemes based on negative-sequence comp... [more]

Local authorities are well placed to realise co-benefits of integrated local energy systems; however, in the UK they have no statutory energy mandate. Planning and developing clean energy are discretionary, and persistent budget reductions, combined with the lack of strategic direction from the UK government for more localised energy provision, limit local capacity, expertise and resources. Nevertheless, some local authorities have led energy initiatives but have been unable to stimulate investment at the pace and scale required to align with net zero greenhouse gas targets. Using evidence from such initiatives, this paper discusses the institutional changes needed to enable local authorities to act. It examines existing climate and local energy plans, and their integral socio-economic value. Using this evidence, investment opportunities from locally led net zero programmes are identified. EU technical assistance funds provided a particularly successful route to local energy developmen... [more]

With the continuous improvement of automatization of underground oil and gas resources exploitation, more and more instructions are required for the control technology while drilling in complex processes. The conventional downlink communication technology has shortcomings, such as data transmission lag and high bit error rate, which cannot meet the actual needs. Therefore, developing a new high-speed and low bit error rate (BER) downlink communication technology is very important. In this study, a new type of downlink communication system based on the electric current field is designed. Firstly, based on the theory of electromagnetic field and electromagnetic wave, the current distribution model of the drill string is established. Then, the magnetic field distribution model of the drill string is deduced according to the research on the static electromagnetic field and boundary problems. Finally, the ground simulation experiment platform of the downlink communication system is built an... [more]

Hydrogen has been attracting attention as a fuel in the transportation sector to achieve carbon neutrality. Hydrogen storage in liquid form is preferred in locomotives, ships, drones, and aircraft, because these require high power but have limited space. However, liquid hydrogen must be in a cryogenic state, wherein thermal insulation is a core problem. Inner materials, including glass bubbles, multi-layer insulation (MLI), high vacuum, and vapor-cooled shields, are used for thermal insulation. An analytic study is preferred and proceeds liquid hydrogen tanks due to safety regulations in each country. This study reviewed the relevant literature for thermodynamic modeling. The literature was divided into static, dynamic, and systematic studies. In summary, the authors summarized the following future research needs: The optimal design of the structure, including suspension, baffle, and insulation system, can be studied to minimize the boil-off gas (BOG). A dynamic study of the pressure,... [more]

The deployment of a 765-kV transmission line on Eskom’s South African Grid marks the beginning of a new era in power industries. The integration of renewable energies by independent power producers (IPPs) leads to an infrastructural change in the stability performance of the entire grid. These developments are expected to bring about a multiterminal direct current (MTDC) system for practical implementation on this grid. Therefore, this study focuses on the dynamic response of the South African transmission grid during a system disturbance. In the carrying out of this study, the South African grid was modeled on PSCAD, and its performance was evaluated. The impact of the MTDC link on the grid’s interarea oscillation was also investigated. An additional current order controller for the MTDC link was developed, and its impact on the MTDC power transfer was analyzed. The results show a better system performance and reduced interarea power swings with the inclusion of the MTDC link.

PV-Battery systems are commonly sized based on the lowest solar radiation of the site of implementation. This implies that during days of high solar radiation excess energy is available. This study investigated the potential of excess energy for thermal storage from PV systems for a case of a rural health center. The system components of a typical PV installation in a rural health center in Tigray, Ethiopia, were considered. The electricity load profile of the health center and solar radiation data available from Mekelle city were used as inputs to a TRNSYS model. Analysis of excess energy in the system at hourly and ten-minute time intervals was conducted. The analysis results indicate that during the months from September to May excess energy was available that could be thermally stored and utilized. During these months, the excess peak power ranged from 737 to 841 W and daily average excess energy ranged from 2070 to 2959 Wh. In contrast, in the months from June to August, no excess... [more]

Reducing office buildings’ energy consumption can contribute significantly towards carbon reduction commitments since it represents ∼40% of total energy consumption. Major components of this are lighting, electrical equipment, heating, and central cooling systems. Solid evidence demonstrates that individual occupants’ behaviors impact these energy consumption components. In this work, we propose the methodology of using virtual choreographies to identify and prioritize behavior-change interventions for office users based on the potential impact of specific behaviors on energy consumption. We studied the energy-related office behaviors of individuals by combining three sources of data: direct observations, electricity meters, and computer logs. Data show that there are behaviors with significant consumption impact but with little potential for behavioral change, while other behaviors have substantial potential for lowering energy consumption via behavioral change.

To address the problem that a single energy management strategy cannot adapt to complex driving conditions, in this paper, a real-time energy management strategy for different driving conditions is proposed to improve fuel economy. First, in order to improve the accuracy and stability of the driving condition identifier, a feature fusion extreme learning machine (FFELM) is used for identification. Secondly, equivalent consumption minimization strategy (ECMS) offline optimization is conducted for different types of driving cycles, and the effect of driving cycle type and driving distance on the energy management strategy under the optimization result is analyzed. A real-time energy management strategy combining driving cycle type, driving distance, and optimal power allocation factor is proposed. To demonstrate the effectiveness of the proposed strategy, combined driving cycles were used for testing. The simulation results show that the proposed strategy can improve the equivalent fuel... [more]

Over 30% of the world’s land area is covered by forests. Approximately 761 million m3 of wood is harvested annually in Europe (2017). The aim of the paper is to assess the amount of wood (biomass) produced in Europe per year, as it determines the amount of carbon dioxide released from wood because of combustion for heating and energy purposes. The circular bioeconomy was applied as the theoretical framework for this study. The study employs official statistics on material flows and also uses a technology assessment, which allows for more precise estimations. It can be estimated that 110 million tons of harvested woody biomass are converted into energy every year. This constitutes nearly 69% of processed wood, with burned wood treated as zero-emission. From the analysis of the compiled results, it can be concluded that, in Europe, more than 50% of the mass of raw wood material harvested per year is used for energy in the first stage of processing by manufacturing industries. These proce... [more]

The evaluation of caprocks’ sealing capacity is exceedingly important for depleted gas reservoirs to be reconstructed into gas storage. In this paper, based on the physical sealing mechanism of caprock, four aspects of ten indexes of caprock quality evaluation were firstly selected, and the related classification standards were established. Secondly, based on the rock mechanical sealing mechanism, elastic and plastic indexes were selected to characterize the mechanical brittleness of caprock, and a brittleness evaluation method of caprock based on complete stress-strain curves was established. Then, a systematic comprehensive evaluation model (including 5 aspects and 12 evaluation indexes) for the sealing capacity of gas storage caprock was proposed, and the analytic hierarchy process (AHP) was used to determine the weight of the 12 indexes in the evaluation model, and the formula for calculating the suitability of the caprock sealing capacity was established. Finally, the geological d... [more]

The geological sequestration of CO2 in deep saline aquifers is one of the most effective strategies to reduce greenhouse emissions from the stationary point sources of CO2. However, it is a complex task to quantify the storage capacity of an aquifer as it is a function of various geological characteristics and operational decisions. This study applies physics-based proxy modeling by using multiple machine learning (ML) models to predict the CO2 trapping scenarios in a deep saline aquifer. A compositional reservoir simulator was used to develop a base case proxy model to simulate the CO2 trapping mechanisms (i.e., residual, solubility, and mineral trapping) for 275 years following a 25-year CO2 injection period in a deep saline aquifer. An expansive dataset comprising 19,800 data points was generated by varying several key geological and decision parameters to simulate multiple iterations of the base case model. The dataset was used to develop, train, and validate four robust ML models—... [more]

Energy crops are dedicated cultures directed for biofuels, electricity, and heat production. Due to their tolerance to contaminated lands, they can alleviate and remediate land pollution by the disposal of toxic elements and polymetallic agents. Moreover, these crops are suitable to be exploited in marginal soils (e.g., saline), and, therefore, the risk of land-use conflicts due to competition for food, feed, and fuel is reduced, contributing positively to economic growth, and bringing additional revenue to landowners. Therefore, further study and investment in R&D is required to link energy crops to the implementation of biorefineries. The main objective of this study is to present a review of the potential of selected energy crops for bioenergy and biofuels production, when cultivated in marginal/degraded/contaminated (MDC) soils (not competing with agriculture), contributing to avoiding Indirect Land Use Change (ILUC) burdens. The selected energy crops are Cynara cardunculus, Arundo... [more]

For deep-buried thick top-coal roadways under high stress, there exists great difficulty in controlling the stability of the surrounding rock as well as in the necessity for low driving speeds. Taking the return air roadway 20201 (RAR 20201) of the Dahaize Coal Mine as the background, this paper presents a typical engineering case of a deep-buried thick top-coal roadway in a western mine. Through methods such as in situ investigation, theoretical analysis, numerical simulation and engineering practice, we studied the deformation and failure mechanisms of the surrounding rock in a deep-buried high-stress thick top-coal roadway, and revealed the driving speed effect. Results show that compared with shallow buried roadways, the deep-buried thick-roof coal roadway suffers a greater range of damage and failure. The roof damage is so deep that it exceeds the action range of bolts, resulting in the stress transferring to both sides, which affects the stability of the roadway surroundings. The... [more]

Low accuracy is the main challenge that plagues the application of engine modeling technology at present. In this paper, correlation analysis technology is used to analyze the main influencing factors of engine torque and NOx (nitrogen oxides) raw emission performance from a statistical point of view, and on this basis, the regression algorithm is used to construct the engine torque and NOx emission prediction model. The prediction RMSE between engine torque prediction value and true value reaches 4.6186, and the torque prediction R2 reaches 1.00. Prediction RMSE between NOx emission prediction value and true value reaches 67.599, and NOx emission prediction R2 reaches 0.99. When using the new WHTC data for model prediction verification, the RMSE between the engine torque predicted value and true value reaches 4.9208, and the prediction accuracy reaches 99.60%, the RMSE between NOx emission prediction value and true value reaches 72.38, and the prediction accuracy reaches 99.2%, indica... [more]

Mechanical and chemical processes experienced by carbonate rocks result in a complex network of natural fractures and dissolution features that have direct implications on porosity, permeability, and connectivity in reservoirs. Characterization of natural fractures is best done in core; however, it can be time-consuming due to the large amounts of individual features present and the long list of attributes typically collected for each feature. Additionally, karst features in core, such as vugs and small cavities, are seldom characterized in a quantitative way or are overlooked. We introduce a new methodology, called the non-matrix quick pass (NMQP), which allows for the collection of non-matrix features in a rapid yet quantitative fashion at a rate of 12 to 20 m of core per hour. The NMQP methodology offers enough vertical resolution so that observations can be integrated with other wellbore data types (e.g., wireline logs, well tests, and production logs). This method also yields esti... [more]

Refracturing treatment is widely used to enhance the well productivity in shale gas reservoirs, particularly for initially fractured wells with low productivity. The principal of this work is based on the transient behavior of pressure and rate for a vertically refractured well in a shale gas reservoir, considering the fracture reorientation and adsorption and desorption property. Based on the point-source theory and Laplace transform, a semi-analytical solution for a refractured well is obtained by coupling the point-source solution of a shale gas reservoir and the solution of artificial fractures. The validation of this new solution is carried out smoothly by comparison with the results from the commercial software COMSOL. Five typical flow regimes are identified on the transient pressure curve, namely bi-linear flow regime, formation linear flow regime, mid-radial flow regime, inter-porosity flow regime, and pseudo-radial flow regime. A groove segment occurs on the transient-pressur... [more]

Short-term car rental services called “car-sharing” or “carsharing” are systems that in recent years have been an alternative form of transport by individual car in an increasing number of cities around the world. With the growing popularity of services, new decision-making problems have arisen among system operators. Among the challenges faced by operators, due to the constantly growing environmental requirements, is the fleet of vehicles for car-sharing systems-appropriate selection. Noticing this research gap, this article was dedicated to determining the criteria that are important when choosing a fleet of vehicles for car-sharing and to indicate the best suited to the needs of car-sharing vehicles. Own research was proposed, considering desk research, expert research and analyses using the multi-criteria decision support method (ELECTRE III). This research was carried out for the Polish market of car-sharing services. Studying the Polish market is appropriate due to the occurrence... [more]

Floor heaving is a phenomenon that occurs in almost all mining roadways and tunnels. It can restrain the advance of the heading face or cause serious problems during roadway use. The highest levels of floor uplifting are observed in coal mines, which can reduce the output or even stop it altogether. The floor heaving intensity depends on the rock type, the stress in the rock mass, and rocks’ mechanical properties. Floor deformation develops when the secondary state of stress is formed around the working, and it is much higher and more dynamic in the case of waterlogged rocks. The presence of water increases the floor’s propensity to heave, especially clay rocks, such as claystones or mudstones, if they include water-absorbed minerals. In this paper, we present a new modeling methodology for roadway floor heave. The modeling covers a dry floor condition in which the parameters of the Hoek-Brown failure criterion are gradually lowered over time, and a waterlogged floor condition, in whic... [more]