The identification of underground formation lithology can serve as a basis for petroleum exploration and development. This study integrates Extreme Gradient Boosting (XGBoost) with Bayesian Optimization (BO) for formation lithology identification and comprehensively evaluated the performance of the proposed classifier based on the metrics of the confusion matrix, precision, recall, F1-score and the area under the receiver operating characteristic curve (AUC). The data of this study are derived from Daniudui gas field and the Hangjinqi gas field, which includes 2153 samples with known lithology facies class with each sample having seven measured properties (well log curves), and corresponding depth. The results show that BO significantly improves parameter optimization efficiency. The AUC values of the test sets of the two gas fields are 0.968 and 0.987, respectively, indicating that the proposed method has very high generalization performance. Additionally, we compare the proposed algo... [more]

The multi-terminal direct current network is expected to commercialize while carrying out projects related to DC power systems worldwide. Accordingly, it is necessary to develop a DC circuit breaker required for the DC power system. A DC circuit breaker should be developed to protect the DC power system and the consumer from the transient state on the line in any case. Currently, the use of power semiconductors increases the performance of DC circuit breakers. However, power semiconductors are expensive and suffer series of losses from frequent failures. Therefore, the DC circuit breaker must have a reliable, stable, and inexpensive structure. We proposed a new type of arc-induction type DC circuit breaker. It consists of a mechanical blocking contact, an induction needle and a superconducting magnet. It blows the arc with an induction needle using the Lorentz force according to the high magnetic field of the superconducting magnet. The arc-induction needle absorbs the arc and flows th... [more]

We investigated the gas storage capacity of thermally carbonized and chemically activated Phyllostachys bambusoides (PB), which is a nature-derived green carbon with an organic porous structure. Samples were thermally treated at 900 °C for 24 h, and then were chemically activated with different amounts of KOH. The pore distribution, surface area, and H2 storage capacity were measured by N2 and H2 gas sorption, up to 847 mmHg (1.13 bar) at 77 K. The CO2 storage capacity was measured up to 847 mmHg (1.13 bar) at 298 K. The maximum gas storage was shown in the sample activated with 6 times gravimetric ratio of chemical agent. It reached 1.86 wt% for H2 and 3.44 mmol/g for CO2. We used multilateral analysis methods (XRD, XPS, Raman spectroscopy, and scanning electron microscope) to identify the factors influencing gas sorption. We found that the amount of oxygen groups influence the enhancement of gas storage capacity. Moreover, the results showed that PB-based porous activated carbon has... [more]

Our research group is developing computational fluid dynamics (CFD)-based software for wind resource and energy production assessments in complex terrain called RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University (RIAM)-Computational Prediction of Airflow over Complex Terrain), based on large eddy simulation (LES). In order to verify the prediction accuracy of RIAM-COMPACT, we conduct a wind tunnel experiment that uses a two-dimensional steep ridge model with a smooth surface. In the wind tunnel experiments, airflow measurements are performed using an I-type hot-wire probe and a split film probe that can detect forward and reverse flows. The results of the numerical simulation by LES are in better agreement with the wind tunnel experiment using the split film probe than the results of the wind tunnel experiment using the I-type hot wire probe. Furthermore, we calculate that the two-dimensional ridge model by changing the length in the spanwise direction, and discu... [more]

In this paper, a 15 kVA soft open point converter is presented. The converter design and manufacturing have been presented in previous papers. The aim of this paper was to show the results of the devices in a full-scale laboratory environment, Gridlab, made of four distribution LV feeders, each rated 40 A. The tests demonstrated the good dynamics of the SOP control and its usefulness in performing a suitable PQ control. They also showed an improvement in the voltage profile and in the load capacity of the overall network. In the final part of the paper, the feedback earned during the development and the test of this first prototype are presented. This feedback will benefit the team for the design of a new improved 50 kVA version.

Boil-off gas (BOG) disposal in liquefied natural gas (LNG) tankers has long been considered inevitable owing to the constant vaporization of the LNG in the storage tanks, but results in energy waste and environmental pollution. To address these challenges, we developed a re-liquification system that can condense the BOG and return it to the storage tank. The re-liquification system was modeled, and a case study was conducted to evaluate the viability of the system. The energy waste, which was quantified by tonnes of oil equivalent (TOE), greenhouse-gas emissions in tonnes of carbon dioxide (TCO2), and cost reduction in millions of U.S. dollars (MUSD), was evaluated for five different tanker cruising speeds. The re-liquification system significantly reduced the average TOE, TCO2, and cost by up to 9120.40 TOE/year, 19,474.33 TCO2/year, and 1.9765 MUSD/year, respectively, for five different tanker speeds with multi-stage compression.

As a key accessory of high-voltage (HV) insulated submarine cable, the factory joints of the cross-linked polyethylene (XLPE) represent an unpredictable uncertainty in cable-connecting fabrications by means of the extruded molding joint (EMJ) technique. The electrical breakdown pathways formed at the interfaces between recovery insulation and cable body under alternative current 500 kV voltages are specifically investigated by microstructure characterizations in combination with the electric field and fractal simulations. Dielectric-defected cracks in tens of micrometers in insulation interfaces are identified as the strings of voids, which dominate insulation damages. The abnormal arrangements of XLPE lamellae from scanning electron microscopy (SEM) imply that the structural micro-cracks will be formed under interface stresses. Electrical-tree inception is expedited to a faster propagation due to the poor dielectric property of interface region, manifesting as 30% lower of tree incept... [more]

This study aims to test the effects of changes in international crude oil prices on changes in crude oil and hydropower use from 1965 to 2016. We suggest a cointegration relationship between the consumption of coal, crude oil, and hydropower and the real crude oil price. The real price is weakly exogenous for the long-run relationship and has impacted energy consumption accordingly. The long-run crude oil price elasticity of oil use is 0.460. Our estimate suggests a positive oil price−oil use relationship in China, which is dramatically different from many previous studies but is consistent with a few past studies. The growth in external oil prices may lead to a long-run increase in hydropower use in China, with a long-run price elasticity of 0.242. The long-run crude oil price elasticity of coal use is −0.930. Hence, increased oil and hydropower use could make up the energy supply−demand gap left over by the decreased coal use. Strictly planned domestic fuel prices and rapidly growing... [more]

In order to encourage hybrid generation of multiple wind/solar/hydro power stakeholders, synergistic gains from hybrid generation should be allocated fairly, efficiently and reasonably to all power stakeholders. This paper explores how cooperative game theory resolves conflicts among multiple wind/solar/hydro power stakeholders. Elaborate allocation processes of the nucleolus, Shapley value and MCRS methods are presented in resolve synergistic gains allocation problems of wind−solar−hydro hybrid generation system with cascade hydropower. By analyzing properties such as existence, uniqueness and rationality, we find that both the Shapley value and MCRS methods are fair, efficient and rational allocation methods whereas the nucleolus method is limited by reservoir volume of hydro power stakeholders. Analyses on computational feasibility show that the Shapley value method may induce combinational explosion problem with the integration of more power stakeholders. A further application in Y... [more]

There is a vital need to understand the flashover process of polymeric insulators for safe and reliable power system operation. This paper provides a rigorous investigation of forecasting the flashover parameters of High Temperature Vulcanized (HTV) silicone rubber based on environmental and polluted conditions using machine learning. The modified solid layer method based on the IEC 60507 standard was utilised to prepare samples in the laboratory. The effect of various factors including Equivalent Salt Deposit Density (ESDD), Non-soluble Salt Deposit Density (NSDD), relative humidity and ambient temperature, were investigated on arc inception voltage, flashover voltage and surface resistance. The experimental results were utilised to engineer a machine learning based intelligent system for predicting the aforementioned flashover parameters. A number of machine learning algorithms such as Artificial Neural Network (ANN), Polynomial Support Vector Machine (PSVM), Gaussian SVM (GSVM), Dec... [more]

The aim and contribution of this paper is to identify with Duval Pentagon 2 the stray gassing (SG) patterns of inhibited and uninhibited mineral oils in transformers in service and in the well-established laboratory SG tests of CIGRE and ASTM, so that SG in transformers can be easily distinguished from the other types of faults occurring in them. The SG test of IEC 60296-2020 is inadequate or much less effective for that purpose.

The development of powered electronic technology has made many aware of the design and control of ship power systems (SPSs), and has made medium voltage DC (MVDC) architecture the main research direction in the future. The negative impedance characteristic of constant power load (CPL) generated by the coupling of powered electronic converters will seriously affect the stability of the systems if these converters are not properly controlled. The conventional linear control method can only guarantee the small-signal stability of the system near its equilibrium point. When the operating point changes in a large range, linear control methods will be ineffective. More importantly, research for the large-signal stability of the multi-converter system with CPLs is still rarely involved. In this paper, a sliding-mode-based duty ratio controller (SMDC) is proposed for voltage regulation and current sharing of the multiple parallelly-connected DC−DC converters system loaded by CPLs. By controlli... [more]

With an ever-increasing release of harmful greenhouse gases into the environment, there is an ongoing search for a renewable source of energy to replace the current means of producing energy. One promising source is from methanotrophic bacteria, which uses methane as its primary carbon source to produce valuable byproducts including lipids. These lipids could be used in the production of biofuels and other important industrial chemicals including plastics and surfactants. The use of methanotrophs would lower the amount of methane in the atmosphere from two sides, in the growth and cultivation of methanotrophs and in the replacement of conventional fossil fuels. The development of such a system requires a good understanding of the bacteria responsible and the steps of growth/culturing and extraction. An integrated system that uses every product of methanotrophic growth could impact multiple markets and help make this technique economically feasible as well as provide the groundwork for... [more]

Overdischarge often occurs during the use of battery packs, owing to cell inconsistency in the pack. In this study, the overdischarge behavior of 2.9 Ah cylindrical NCM811 [Li(Ni0.8Co0.1Mn0.1)O2] batteries in an adiabatic environment was investigated. A higher overdischarge rate resulted in a faster temperature increase in the batteries. Moreover, the following temperatures increased: Tu, at which the voltage decreased to 0 V; Ti, at which the current decreased to 0 A; and the maximum temperature during the battery overdischarge (Tm). The following times decreased: tu, when the voltage decreased from 3 to 0 V, and ti, when the current decreased to 0 A. The discharge capacity of the batteries was 3.06−3.14 Ah, and the maximum discharge depth of the batteries was 105.51−108.27%. Additionally, the characteristic overdischarge behavior of the batteries in a high-temperature environment (55 °C) was investigated. At high temperatures, the safety during overdischarging decreased, and the amou... [more]

This article presents a comparative analysis of energy governance with respect to renewable energy sources in Ecuador. The use of renewable energy sources increases energy security and enables countries to achieve their climate mitigation goals. Ecuador’s energy mix is dominated using fossil fuels and produces only 7.8% of its energy supply from renewable energy. The scenario analysis suggests that using the example of international renewable energy policies will achieve sustainable energy development in Ecuador. Relying less on fossil fuels and decentralizing the electricity sector from the use of thermoelectric plants is the great challenge for the country. Using the enormous water potential that Ecuador has and taking advantage of the sources of solar, biomass and wind energy available in the country will reduce the forecast of 60,233.70 KT CO2 by 2030 that would be reached if current consumption conditions and energy mix are maintained, while designing a long-term energy planning w... [more]

Aiming at the problem of large magnitude and high frequency of common-mode voltage (CMV) when space vector pulse width modulation (SVPWM) is used in a three-phase motor fed by a two-level voltage source inverter, a common-mode reduction SVPWM (CMRSVPWM) is studied. In this method, six new sectors are obtained by rotating six sectors of conventional SVPWM by 30°. In odd-numbered sectors, only three non-zero vectors with odd subscripts are used for synthesis, while in even-numbered sectors, only three non-zero vectors with even subscripts are used for synthesis. The actuation durations of three non-zero vectors in each switching period in each sector are given. Simulation and experimental results show that, compared with the conventional SVPWM, the CMV magnitude of CMRSVPWM is reduced by 66.67% and the CMV frequency of CMRSVPWM is reduced from the original switching frequency to the triple fundamental frequency. At the same time, the current, torque and speed of the motor are still good.

In deep geothermal boreholes, an effect of temperature (so-called thermal lift) is observed, which results in the volumetric expansion of the fluid extracted. This process results in increased wellhead pressure values being recorded; in the absence of an appropriate correction, hydraulic properties of the reservoir layer cannot be properly determined. As an example of this effect, the Chochołów PIG-1 (CH PIG-1) geothermal borehole situated in Podhale Basin in Poland was used. Hydrodynamic tests including two pumping phases were carried out in the well in order to establish the basic hydraulic properties related to the determination of its operational resources (maximum water extraction value−capacity) and permissible groundwater level. Particular attention was paid to the thermal lift effect in the borehole. The conductivity, which depends on the pumping level, could be two to three times higher with temperature correction than results without any correction. The goal was to analyse th... [more]

Because of the noncontact structure of wireless power transfer (WPT) systems, foreign metal objects can easily enter into the coupling region—and often move under the action of electromagnetic force (EMF), instead of staying relatively static, which brings a difficult problem for foreign object detection technology. In this paper, we investigate the motion state of foreign metal objects with different properties under the action of electromagnetic force in the coupling space of WPT system. The equivalent model of the circuit parameters with the intervention of foreign metal objects and the differential equations for the motion of foreign metal objects are derived. Combined with finite-element simulation calculations, the motion characteristic of ferromagnetic and non-ferromagnetic metals under EMF was analyzed. The results show that, due to the size and properties of the metal, non-ferromagnetic foreign metal objects have four states: vibration, suspension, static and flying out. The f... [more]

A small Counter-Rotating Wind Turbine (CRWT) has been proposed and its performance has been investigated numerically. Results of a parametric study have been presented in this paper. As parameters, the axial distance between rotors and a tip speed ratio of each rotor have been selected. Performance parameters have been compared with reference to a Single Rotor Wind Turbine (SRWT). Simulations were carried out with Computational Fluids Dynamics (CFD) solver and a Large Eddy Scale approach to model turbulences. An Actuator Line Model has been chosen to represent rotors in the computational domain. Summing up the results of simulation tests, it can be stated that when constructing a CRWT turbine, rotors should be placed at a distance of at least 0.5 D (where D is rotor outer diameter) or more. One can then expect a noticeable power increase compared to a single rotor turbine. Placing the second rotor closer than 0.5 D guarantees a significant increase in power, but in such configurations,... [more]

Real-time simulation is an increasingly popular tool for product development and research in power systems. However, commercial simulators are still quite exclusive due to their costs and they face problems in bridging the gap between two common types of power system simulation, conventional phasor based, and electromagnetic transient simulation. This work describes recent improvements to the open source real-time simulator DPsim to address increasingly important use cases that involve power electronics that are connected to the electrical grid and increasing grid sizes. New power electronic models have been developed and integrated into the DPsim simulator together with techniques to decouple the system solution, which facilitate parallelization. The results show that the dynamic phasors in DPsim, which result from shifted frequency analysis, allow the user to combine the characteristics of conventional phasor and electromagnetic transient simulation. Besides, simulation speed up tech... [more]

An important element of a solar installation is the storage tank. When properly selected and operated, it can bring numerous benefits. The presented research relates to a project that is implemented at the Solar Energy Research Center of the University of Almeria in Spain. In order to improve the operation of the solar cooling and heating system of the Center, it was upgraded with two newly designed storage tanks filled with phase change materials (PCM). As a result of design works, commercial material S10 was selected for the accumulation of cold, and S46 for the accumulation of heat, in an amount of 85% and 15%, respectively. The article presents in detail the process of selecting the PCM material, designing the installation, experimental research, and exergy analysis. Individual tasks were carried out by research groups cooperating under the PCMSOL EUROPEAN PROJECT. Results of tests conducted on the constructed installation indicate that daily energy saving when using a solar chille... [more]

The energy storage field is nowadays a highly ranking topic. This research deals with the installation and analysis of the ice storage system which combines heat pump, solar absorber, and ice storage tank (phase change material—PCM). This system uses a special kind of solar absorber − header pipes (HDP), which have no thermal isolation compared to the common solar absorber. Thanks to that the HDP, pipes can absorb thermal energy not only from the sun but also from the environment. The rain or snow also affects heat exchange. All that is provided by one technical device. The system can store thermal energy gained from the solar absorber into the ice storage tank for future usage. Research works with data from the real operation, for a period of the year covering all working phases/modes of the system. The analysis of the data led to the identification of several specific modes of the system, especially from the processes taking place in the PCM storage tank during its charging and disch... [more]

Air pollution has become an increasingly serious environmental problem in China. Especially in winter, the air pollution in northern China becomes even worse due to winter heating. The “coal to gas” policy, which uses natural gas to replace coal in the heating system in winter, was implemented in Beijing in the year 2013. However, the effects of this policy reform have not been examined. Using a panel dataset of 16 districts in Beijing, this paper employs a first difference model to examine the impact of the “coal to gas” policy on air quality. Strong evidence shows that the “coal to gas” policy has significantly improved the air quality in Beijing. On average, the “coal to gas” policy reduced sulfur dioxide (SO2), nitrogen dioxide (NO2), particulate matter smaller than 10 µm (PM10), particulate matter smaller than 2.5 µm (PM2.5) and carbon monoxide (CO) by 12.08%, 4.89%, 13.07%, 11.94% and 11.10% per year, respectively. We find that the “coal to gas” policy is more effective in areas... [more]

Asset-management accounts for a significant share of grid operators’ influenceable costs, which are under high economic pressure due to deregulation. In asset-management, visual inspections are the main measure to determine asset conditions. In the context of digitalization, we propose a concept to acquire additional information about the condition of distribution substations and to derive flexible inspection intervals from this information, in contrast to fixed intervals that are common in scientific literature and practice. Thus, knowledge about the substations increases, inspection intervals can be expanded dynamically, and significant cost savings are possible, which we demonstrate by the example of a German distribution grid operator.

The National Electric Energy Agency (ANEEL) of Brazil, in a bid to encourage energy-conscious energy consumption, has proposed a new sustainable energy tariff modality (the White Tariff) based on off-peak usage. This study aims to compare and contrast situations in which the White Tariff alone is used, and where it is combined with power generation from a generator set or a photovoltaic cell energy system to reduce energy costs. Furthermore, economic, environmental, and social advantages are outlined in the project summaries. Interviews and documentary analyses were conducted in a technology park that uses only the White Tariff and in condominiums that combine the White Tariff with a generator set or a photovoltaic cell system. The data generated was fed into the database of the Horosazonal software to obtain an overview of these companies. Results show that the company adopting the White Tariff alone achieved 19% and US$14,684 in annual savings. However, when the White Tariff is combi... [more]