Insulators are considered one of the most significant parts of power systems which can affect the overall performance of high-voltage (HV) transmission lines and substations. High-voltage (HV) insulators are critical for the successful operation of HV overhead transmission lines, and a failure in any insulator due to contamination can lead to flashover voltage, which will cause a power outage. However, the electrical performance of HV insulators is highly environment sensitive. The main cause of these flashovers in the industrial, agricultural, desert, and coastal areas, is the insulator contamination caused by unfavorable climatic conditions such as dew, fog, or rain. Therefore, the purpose of this work is to review the different methods adopted to identify the contamination level on high-voltage insulators. Several methods have been developed to observe and measure the contamination level on HV insulators, such as leakage current, partial disgorgement, and images with the help of dif... [more]

Multi-criteria decision analyses (MCDAs) have been developed to support and evaluate decision-making on multi-layered problems. The benefit lies in creating transparency, among other benefits, especially in tackling divergent stakeholder interests. Within the energy transition, area shortage can lead to sustainability trade-offs, calling for the reconciliation of planning processes and satisfactory compromises. While ex ante MCDAs complement planning, the ex post consideration of processes has been less widely studied. Using a case study of offshore wind energy (OWP) within German marine spatial planning, we investigated the shifting weights of sustainability criteria and stakeholder interests. A multi-criteria approach (Preference Ranking Organization Method for Enrichment of Evaluations (PROMETHEE)) addressed how decision-making can be iteratively traced, and the winners and losers indicated in sustainability dilemmas, such as between climate and biodiversity implications. Findings i... [more]

The present paper describes the research on the mechanism of inrush current formation in a modern single-phase transformer, in which the insulation system must withstand the stresses arising during these transient states. A complete and measurement-verified method for determining the transformer inrush current waveforms and other signals (e.g., fluxes and voltages) is developed. This method makes it possible to determine a steady state solution. However, on account of the electromagnetic phenomena, the solving process is long. To analyze the transient dynamic response of the tested transformer, a nonlinear model was assumed, from which the stiff differential equations were derived. The simulation analyses were performed using dedicated software written in C# with the original implementation of the five-stage Radau IIA algorithm selected from the known variants of the Runge−Kutta implicit methods. The calculations were based on the measurement waveforms recorded during transient (switch... [more]

The largest ultra-deep (>6000 m) strike-slip fault-controlled oilfield in the world is found in the Tarim Basin of Northwestern China. The localized fractured reservoirs are the major production targets along the strike-slip fault zones. Different from its use in the primary porous-type reservoirs, however, the conventional technology is not favorable for use in oil/gas development in Ordovician carbonate reservoirs. For this reason, high-density seismic acquisition and high-resolution seismic processing were carried out to provide high-precision data for fault and fractured reservoir identification. In addition, the multi-filtering process and the maximum likelihood method are typically used to identify small faults and fault segments along a strike-slip fault zone. Further, seismic facies-constrained inversion and amplitude attributes are favorable for large fracture-cave reservoir description. With the advancements in seismic technology, the high and stable production well ratio has... [more]

The high-resolution seismic characterization of gas hydrate reservoirs plays an important role in the detection and exploration of gas hydrate. The conventional AVO (amplitude variation with offset) method is based on a linearized Zoeppritz equation and utilizes only the reflected wave for inversion. This reduces the accuracy and resolution of the inversion properties and results in incorrect reservoir interpretation. We have studied a high-resolution wave-equation-based inversion method for gas hydrate reservoirs. The inversion depends on the scattering integral wave equation that describes a nonlinear relationship between the seismic wavefield and the elastic properties of the subsurface medium. In addition to the reflected wave, it considers more wavefields including the multiple scattering and transmission during inversion to improve the subsurface illumination, so as to enhance the accuracy and resolution of the inversion properties. The results of synthetic data from Pearl River... [more]

A theoretical evaluation of the biochar production process using a biomass gasifier has been carried out herein. Being distinguished from the previous research trend examining the use of a biomass gasifier, which has been focused on energy efficiency, the present study tries to figure out the effect of biochar production rate on the overall process performance because biochar itself has now been given a spotlight as the main product. Biochar can be utilized for agricultural and industrial purposes, along with the benefit of climate change mitigation. A thermodynamic model based on chemical equilibrium analysis is utilized to demonstrate the effect of biochar production rate on the producer gas characteristics such as gas composition, LHV (lower heating value) and cold gas efficiency. Three gasifier models using chemical equilibrium model are reconstructed to simulate biochar-producing gasifiers, and seven kinds of biomass are considered as feed material. Depending on the assumptions ap... [more]

To enable the fast growth of the floating offshore wind industry, simulation models must be validated with experimental data. Floating wind model-scale experiments in wind−wave facilities have been performed over the last two decades with varying levels of fidelity and limitations. However, the turbine controls in these experiments have considered only limited control strategies and implementations. To allow for control co-design, this research focuses on implementing and experimentally validating more advanced turbine control actions and strategies in a wind−wave basin for a 1:70-scale model of the International Energy Agency’s wind 15 MW reference wind turbine. The control strategies analyzed include torque control, collective pitch control, and transition region control (setpoint smoothing). Our experimental and numerical results include the effects of varying rotor speeds, blade pitches, and wind environments on the turbine thrust and torque. Numerical models from three different s... [more]

The journal retracts the article “A Critical Review on Recycling Composite Waste Using Pyrolysis for Sustainable Development” Energies 2021, 14(18), 5748 [...]

This paper presents a combined experimental−analytical investigation of coal strain development under fluctuating applied hydrostatic stress. The laboratory setup mimics the isotropic volumetric compaction of coal under burial−uplift cycles in the absence of tectonic stress. Special emphasis is placed on the corresponding permeability evolution of the coal strata. Our results show that the stress−strain path is exponential, approaching a linear relation in the logarithmic stress−strain space with the monotonic increase in stress. A similar behavior is found for the strain−permeability path in the logarithmic strain−permeability space. The permeability recovery undergoes hysteresis with respect to the stress in a stress loading−unloading cycle, but the hysteresis is not manifest with respect to the strain. A theoretical geomechanical consolidation analysis was performed using an elastoplastic modelling framework. The analysis suggests that plastic strain is the cause of the hysteresis o... [more]

To cope with the increasing energy demand, power systems, especially distribution networks, face many challenges. Recently, these networks have become complex and large, and their stability and reliability are not easy to be handled. The integration of renewable energy resources and at the same time limiting their accompanied high fault currents is one of the approvable suggestions. Many solutions have appeared to restrict the fault currents, but fault current limiters (FCLs) arise as an efficient and promising solution to whether to interrupt or limit the fault currents to allowable limits. This paper presents a literature review of the integration of renewable energy resources as distributed generation units (DGs) and FCLs in distribution networks. The DGs can be categorized based on their size and ability to deliver active or reactive power in addition to their fuel. All of solar, wind, water, biomass, geothermal, and fuel cell are utilized as the main engine for these units. Additi... [more]

Current power systems are undergoing an energy transition, where technological elements such as distributed generation and electric vehicles through AC or DC microgrids are important elements to face this transition. This paper presents a methodology for quantifying distributed resource-based generation and the number of electric vehicles that can be connected to isolated DC grids without impacting the safe operation of these networks. The methodology evaluates the maximum capacity of distributed generation considering the uncertainty present in the electric vehicle charging of fleets composed of five types of electric vehicles. Specifically, the uncertainty is associated with the following variables: the home arrival time, home departure time, traveled distance, and battery efficiency. The methodology was applied to a 21-bus DC microgrid and a 33-bus DC network under different test conditions. The results show that higher penetrations of EVs and distributed resource-based generation c... [more]

Energy determines the social, economic, and environmental aspects that enable the advancement of communities. For this reason, this paper aims to analyze the quality of the energy service in the Non-Interconnected Zones (NIZ) of Colombia. For this purpose, clustering techniques (K-means, K-medoids, divisive analysis clustering, and heatmaps) are applied for data analysis in the context of the NIZ to identify patterns or hidden information in the Colombian government data related to the state of the electricity service in these localities during the years 2019−2020. A descriptive statistical analysis and validation of the results of the clustering techniques is also carried out using R software. Through the implementation of clustering algorithms such as K-means, K-medoids, and divisive analysis clustering, potential areas for the development of renewable and alternative energy projects are identified, considering places with deficiencies in their current electricity service, higher con... [more]

The review presents the D2-law of droplet evaporation, which is used to describe the spraying process involving the evaporation of droplets. This law, the subject of numerous publications, can be successfully applied to describe the droplet evaporation process under various conditions, including the calculations of the process of feeding the boiler with a liquid that contains catalyst particles. To date, not a lot of work has been devoted to this issue. The paper is a continuation of previous research concerning the spraying of liquids with a catalyst, which improves the efficiency of the process. The conducted analysis showed that the experimental data from previously published work are very compatible with the data obtained from the D2-law of droplet evaporation. At the standard speed of about 20 m/s of an aerosol flowing through a dust duct, droplets in the stream should be observed up to a distance of 1 m from the outlet of the apparatus supplying the system. Under such flow condit... [more]

Redox flow batteries (RFBs) are a promising candidate that are capable of meeting the energy storage applications to fulfill the needs of renewable resources. Herein, we prepare an electrochemical device that holds higher energy density. In this work, a reusable glucose kit used as a flow cell which in turn helps to minimize the cost and also balance the pump losses in electrochemical systems. For fabricating RFB, ZnO, from the metal organic framework (Zn-MOF/ZnO), uses an electrode material: ZnCl2 in aqueous KOH used as both anolyte and catholyte solution. Upon the new cell fabricating in this investigation, we demonstrated the voltage efficiency of 92% at 5 mA cm−2, which reduces the cost of the cell upon being implemented in the flow battery application.

Due to the complexity of the sedimentary and diagenetic processes, natural rocks generally exhibit strong heterogeneity in mineral composition, physicochemical properties, and pore structure. Currently, 3D printed (3DP) rock analogs fabricated from sandy materials (silica sand) are widely applied to study the petrophysical and geomechanical characteristics of reservoir rocks, which provides an alternative and novel approach for laboratory tests to calibrate the environmental uncertainties, resolve up-scaling issues, and manufacture customized rock specimens with consistent structure and controllable petrophysical properties in a repeatable fashion. In this paper, silica sand with various grain sizes (GS) and Furan resin were used to fabricate rock analogs with different layer thicknesses (LTs) using the binder-jetting 3DP technique. A comprehensive experimental study was conducted on 3DP rock analogs, including helium porosity measurement, micro-CT scanning, SEM, and uniaxial compressi... [more]

There are considerable power losses in Indonesia’s SUMBAGUT 150 kV transmission High Voltage Alternating Current Network (HVAC) system. These power losses and the voltage profile are critical problems in the transmission network system. This research provides one possible way to reduce power losses involving the use of a High Voltage Direct Current (HVDC) network system. Determining the location to convert HVAC into HVDC is very important. The authors of the current study used Particle Swarm Optimization (PSO) to determine the optimal location on the 150 kV SUMBAGUT HVAC transmission network system. The study results show that, before using the HVDC network system, the power loss was 68.41 MW. On the other hand, power loss with the conversion of one transmission line to HVDC was 57.31 MW for “Paya Pasir−Paya Geli” (efficiency 16.22%), 51.79 MW for “Paya Pasir−Sei Rotan” (efficiency 24.29%), and 60.8 MW for “Renun−Sisikalang” (efficiency 110.12%). The power loss with the conversion of t... [more]

The proliferation of matrix converter interfaces coupled with traditional loads produces nonstandard and high-frequency harmonics in the range of (2 to 150) kHz in the power system. Although several research works have been conducted on passive and active filter solutions, most of these are low-frequency (below 2 kHz) solutions and are not effective under supraharmonic frequencies. An experimental study of a fuzzy-inference-system-controlled hybrid active power filter (HAPF) for the attenuation of higher frequency harmonics (above 8 kHz) is proposed. The compensational approach introduced is different from traditional approaches and the use of the fuzzy logic controller eliminates complexities involved in active filter designs. The proposed filter obtained a total harmonic distortion (THD) of 1.16% of the fundamental 50 Hz supply frequency. The performance of the proposed hybrid filter was compared with that of the proportional and integral (PI) controlled topology. The results obtaine... [more]

Intelligent power grid fault diagnosis is of great significance for speeding up fault processing and improving fault diagnosis efficiency. However, most of the current fault diagnosis methods focus on rule diagnosis, relying on expert experience and logical rules to build a diagnosis model, and lack the ability to automatically extract fault knowledge. For switch refusal events, it is difficult to determine a refusal switch without network topology. In order to realize the non-operating switch identification without network topology, this paper proposes a power grid fault diagnosis method based on deep reinforcement learning for alarm information text. Taking the single alarm information of the non-switch refusal sample as the research object, through the self-learning ability of deep reinforcement learning, it learns the topology connection relationship and action logic relationship between equipment, protection and circuit breakers contained in the alarm information, and realizes the... [more]

Micro/nano-motors play an important role in energy, environment, and biomedicines. As a new type of nano-motors, nanobottles attract great attention due to their distinct advantages of a large cavity, high specific surface area, bionic streamline structure, and chemotactic motion. Here, we systematically review the development of nanobottle motors from aspects of propulsion mechanisms, fabrication methods and potential applications. Firstly, three types of propulsive modes are summarized, with focus on chemical propulsion, light driving and magnetic actuation. We then discuss the fabrication methods of nanobottles, including the soft-template-based hydrothermal method and the swelling-inducement and wet-chemistry methods. The potential applications of nanobottle motors are additionally highlighted in energy, environmental, and biomedical fields. Finally, the future challenges and outlooks of nanobottle motors are discussed for the further development of this technology.

The No. 2 gas field in the X depression is a low-permeability tight reservoir with a complex lithology, pore structure, and strong physical heterogeneity, and the conventional core porosity−permeability regression method does not meet the requirements of fine evaluation in terms of the accuracy of permeability calculation. The flow unit method has great advantages in improving the accuracy of permeability calculation, but the FZI calculation method is too ideal and weakens the influence of the pore structure’s heterogeneity, and it needs to be verified that the FZI in the study area has a good correlation with the pore structure before it can be used. Therefore, based on analyzing the permeability control factors of low-permeability tight reservoirs, we analyze the correlation between three pore structure characterization parameters and the flow unit index FZI, which proves that the flow unit index FZI in this area can characterize the permeability difference within different flow unit... [more]

The main purpose of the work was examining various methods of decomposition of a network optimization problem of simultaneous routing and bandwidth allocation based on Lagrangian relaxation. The problem studied is an NP-hard mixed-integer nonlinear optimization problem. Multiple formulations of the optimization problem are proposed for the problem decomposition. The decomposition methods used several problem formulations and different choices of the dualized constraints. A simple gradient coordination algorithm, cutting-plane coordination algorithm, and their more sophisticated variants were used to solve dual problems. The performance of the proposed decomposition methods was compared to the commercial solver CPLEX and a heuristic algorithm.

The authors propose a new method of predictive replacements of belt sections in a conveyor belt loop with their refurbishment based on their condition recognized by specially designed diagnostic devices: DiagBelt and BeltSonic. Selection of the moment for belt replacement is made on the basis of forecasted state of its wear, when steel cable failure density exceeds the selected threshold or the percentage of belt covers abrasion exceeds the permissible level. The use of double belt refurbishment extends the total belt operation time, but without diagnostics, the reconditioning success rate is relatively low. Visual inspection allows only an uncertain assessment of cable condition. New devices give precise assessment of their condition and allow the selection of a non-linear rate of belt condition based on consecutive scans. The assessed condition of the cables is the key factor in successful belt refurbishment and obtained cost savings. Additionally, diagnostics can help extend belt li... [more]

This article presents a deep theoretical analysis of the Active Disturbance Rejection Control (ADRC) regulator for the control of first-order systems, directly compared to a “traditional” Proportional Integral (PI) regulator. To complete the theoretical study, ADRC and PI are implemented into the model of a single-phase Dual Active Bridge (DAB) converter to regulate the voltage of a Direct Current (DC) network. Facing different types of disturbances and DC network parameters variations, strengths and weaknesses of the two controllers are highlighted. ADRC and PI controls are discretized and implemented in Control Hardware In the Loop (CHIL) simulations of a single-phase DAB converter to regulate the voltage of a node of multi-terminal and multi-level DC network. By changing the DAB connection points along the MVDC network, the controlled system is stressed with different disturbances, extending the result of single-terminal network software simulations.

Oil well cement microcracks cause formation fluid channeling, compromising oil and gas extraction safety. Superabsorbent polymer (SAP) can absorb water and swell to prevent fluid channeling. In this study, an alkali-resistant and pH-sensitive SAP was prepared based on the properties of oil well cement slurry. The preparation of the SAP was optimized, including monomer ratio, cross-linking agent dosage, and monomer concentration. The pH sensitivity and alkali resistance of the SAP were evaluated. The results revealed that the SAP exhibited good pH sensitivity, with the absorption rate in water being 2.18 times that of cement slurry filtrate (CSF) at 95 °C. Furthermore, the FTIR spectrum showed that the SAP had a stable molecular structure. The secondary absorption rate in water of the SAP after soaking in CSF was not different from the original absorption rate. Styrene−butadiene latex (SBL) can be used to adjust the SAP’s absorption rate. The SAP’s absorption rate had a good exponential... [more]

Since high-voltage direct current (HVDC) systems are very expensive and operationally critical, these systems must be tested before they are put into service. Insulation and performance tests are the two main subjects of these tests. AC voltage tests, as part of the insulation tests, should be performed after system installation is complete and before commissioning. However, in this study, the objective was to perform these tests during the prototype phase of VSC HVDC. Unlike other studies, this study attempted to use COMSOL Multiphysics to determine in advance the problems that may occur in the real system. In this regard, the busbars connecting the submodules of the VSC HVDC system were first modeled in 3D, and the tests to be performed were simulated using COMSOL Multiphysics software. During the simulation, the finite element method (FEM) was used to identify critical points that could cause partial discharge. To validate the simulation results, partial discharge tests on a real sy... [more]