The article describes a case study when the voltage collapse during lightning impulse tests of new power transformers was noticed and when the repeated tests finished with a positive result. The step-by-step process of reaching the conclusion on the basis of dissolved gas analysis (DGA) as a key method of the investigations was presented. The considerations on the possible source of the analysis showed that the Duval triangle method, used in the analysis of the concentration of gases dissolved in oil samples taken from bushings, more reliably and unambiguously than the ratio method recommended in the IEC 60599 Standard, indicated a phenomenon which was identified in the insulation structure of bushings analyzed. Additionally, the results from DGA were found to be consistent with an internal inspection of bushings, which showed a visible trace of discharge on the inside part of the epoxy housing, as a result of the lightning induced breakdown.

In the present study, the effect of different kinds of impellers with different baffles or no baffle was investigated. Up-pumping pitched blade turbine (PBTU) and Rushton turbine (RT) were the two types of impellers tested. The reactor was equipped with different designs of baffles: full, half and surface baffles or no baffles. Single (PBTU or RT) and dual (PBTU/PBTU or RT/RT) use of impellers with full (FB), half (HB), surface (SB) and no baffle (NB) combinations formed two sets of 16 experiments. There was estimation of rate of hydrate formation, induction time, hydrate productivity, overall power consumption, split fraction and separation factor. In both single and dual impellers, the results showed that RT experiments are better compared to PBTU in rate of hydrate formation. The induction time is almost the same since we are deep in the equilibrium line while hydrate productivity values are higher in PBTU compared to RT experiments. As general view RT experiments consume more energ... [more]

The projected increase in the availability of gaseous fuels by growing popularity of household natural gas (NG) filling stations and the increase in the production of gaseous biogas-derived fuels is conducive to an increase in the use of NG fuel. Currently, natural gas in various forms (compressed natural gas (CNG), liquefied natural gas (LNG)) is popular in maritime, rail and road transport. A new direction of natural gas application may be non-road mobile machines powered by a small spark-ignition engine (SI). The use of these engines in the wood chippers can cause the reduction of machine costs and emissions of harmful exhaust gases. In addition, plant material chippers intended for composting in bio-gas plants can be driven by the gas they are used to produce. The biogas can be purified to bio-methane to meet natural gas quality standards. The article presents the design of the natural gas supply system, which is an upgrade of the Lifan GX 390 combustion engine spark ignition engin... [more]

The main goal of this work was to conduct a comparative analysis of the electrical properties of the silicon implanted with neon ions, depending on the dose of ions and the type of substrate doping, for the possibility of generating additional energy levels by ion implantation in terms of improving the efficiency of photovoltaic cells made on its basis. The article presents the results of research on the capacitance and conductance of silicon samples doped with boron and phosphorus, the structure of which was modified in the implantation process with Ne+ ions with energy E = 100 keV and different doses. The analysis of changes in electrical properties recorded at the annealing temperature of the samples Ta = 298 K, 473 K, 598 K, 673 K, and 873 K, concerned the influence of the test temperature in the range from 203 K to 373 K, as well as the frequency f from 100 Hz to 10 MHz, and voltage U from 0.25 V to 2 V. It was possible to detect intermediate bands in the tested samples and determ... [more]

Vehicle transmission which has discrete gear-stages inevitably produces torque drop during shifting gears. This torque drop should be minimized because it may lead to uncomfortable driving feeling and degradation of acceleration performance. In accordance with the spread of electric-powered vehicle technology, this study proposes novel transmission architecture to eliminate torque drop during shifting gears by using one electric motor and verifies its operating concept through experiments with a test-bench. The proposed transmission, called CGST (clutchless geared smart transmission) can synchronize the gear-shaft to be engaged for the next gear-stage with the output shaft by using a planetary gear-set and an electric motor. The CGST has a dual input gear-box with even and odd gear-stages on different input shafts, and the planetary gear-set and the electric motor control the speeds of each input shafts to smoothly engage the next gear-stage. This idea was verified by the simplified te... [more]

Energy efficiency and management is certainly one of the key drivers of human progress. Thus, the trends in the energy research are a topic of interest for the scientific community. The aim of this study is to highlight global research trends in this field through the analysis of a scientific journal indexed exclusively in the energy and fuels category. For this purpose, a journal has been selected that is in the center of the category considering its impact factor, which is only indexed in this category and of open access, Energies of the publisher MDPI. Therefore, a bibliometric analysis of all the contents of the journal between 2008 and 2020, 13,740 documents published, has been carried out. Analyzing the articles that are linked to each other by their citations, 14 clusters or research topics have been detected: smart grids; climate change−electric energy community; energy storage; bioenergy sources; prediction algorithms applied to power; optimization of the grid link for renewab... [more]

An important trend of Building Integrated Solar Thermal (BIST) system is to improve the aesthetic aspect of the solar collector to meet the requirement of architectural style and energy collection. Painting on the glass cover in an appropriate method is a simple and practical way. In this study, a halftone coating was used to print a red brick wall pattern on the glass cover. A series of comparative experiments were carried out to test the effect of the coating on the thermal behavior of the solar collector. In heat collection processes, compared with the solar collector with blank cover plate, the one with coated cover plate has lower absorber plate temperature and higher cover plate temperature. The lower the solar irradiance, the smaller the effect of color coating on the solar collector. Compared with the uncoated surface, the coated surface is more sensitive to solar irradiation. In the same heat collection process, compared with the solar collector coated on the outer surface of... [more]

Air handling units are usually used to maintain the thermal and humidity parameters in indoor swimming pools that are used for lap swimming and recreation. Their use throughout the year consumes much more energy than, for example, air conditioning in residential or office buildings. Their considerable energy consumption is due to the need for their continuous operation to remove moisture gains from the evaporation of water and to heat the air and cover the heat losses of the pool. It is possible to design ventilation devices in such a way that the operating costs will be reduced, and the environmental impact will be significantly reduced. In this article, six different ventilation units in which different heat sources are used to heat the ventilation air have been evaluated; the selection of which was based on the most commonly used solutions. The results of the analysis are aimed to show which of the available heat sources is the most advantageous in terms of global and operating cost... [more]

In view of the disastrous air pollution in the Silesian−Kraków region, reducing emissions from the combustion of conventional fuels is a particularly important issue. Geothermal energy is among the clean and renewable sources of heat that could be used to this end, for instance for recreation or space heating purposes. However, its use in the region is limited, mainly due to insufficient knowledge of the characteristics of the geothermal complexes present. Mesozoic complexes in the region have much smaller energy resources compared to the Polish Lowlands or Podhale, but Paleozoic ones, mainly the Lower Carboniferous and Devonian, offer realistic prospects for energy extraction. The aim of this study was to identify geothermal conditions within the Lower Carboniferous−Devonian complex, primarily in terms of using the waters present there for space heating purposes. The prospective zones identified and indicated during the research are only forecasts, and their actual utility can only be... [more]

Usually thermal response tests are restricted to big geothermal projects; the high investment makes them less suitable for designing domestic low-enthalpy geothermal energy systems. The work here presented aims to study the influence of time reduction in thermal response tests on their precision. Due to the importance of the correct assessment of the thermal characterization of the ground for any kind of geothermal system, time reduction in this essay could make it more affordable to be implemented in some domestic systems. A thermal response test has been implemented, and several time intervals of the test have been considered in order to obtain different results for the thermal conductivity of the ground. The mentioned results have been then compared and also the domestic geothermal systems designed from them by the use of the geothermal software GES-CAL. Results have shown that, in some cases (our testing borehole has some singular characteristics), a significant time reduction in t... [more]

Metal halide perovskites have been investigated for the next-generation light-emitting materials because of their advantages such as high photoluminescence quantum yield (PLQY), excellent color purity, and facile color tunability. Recently, red- and green-emissive perovskite light-emitting diodes (PeLEDs) have shown an external quantum efficiency (EQE) of over 20%, whereas there is still room for improvement for blue emissive PeLEDs. By controlling the halide compositions of chloride (Cl−) and bromide (Br−), the bandgap of perovskites can be easily tuned for blue emission. However, halide segregation easily occurrs in the mixed-halide perovskite under light irradiation and LED operation because of poor phase stability. Here, we explore the effect of A-site cation engineering on the phase stability of the mixed-halide perovskites and find that a judicious selection of low dipole moment A cation (formamidinium or cesium) suppresses the halide segregation. This enables efficient bandgap t... [more]

MgAl2-xGaxCl8 and MgGa2Cl7Br was synthesized from MgCl2, MgBr2, AlCl3, and GaCl3, and the physical properties were evaluated by XRD, AC conductivity, and X-ray fluorescence. MgAl2-xGaxCl8 has the same crystal structure as MgAl2Cl8, belongs to the space group C2/c, and forms a solid solution in all the synthesized compositions. We attempted to MgGa2Cl8-yBry synthesize in the same manner as MgAl2Cl8, but only obtained MgGa2Cl7Br as a single-phase compound. The AC conductivity of MgAl2-xGaxCl8 was lowest for MgAl2Cl8 and highest for MgGa2Cl8. The conductivity of MgGa2Cl8 at 400 K was 1.7 × 10−6 S/cm. The conductivity of MgGa2Cl7Br was higher than that of MgAl2-xGaxCl8 with a value of 1.6 × 10−5 S/cm at 400 K. The formation of Mg metal was observed at the surface of the cathode electrode in an experiment of flowing a direct current using an electrochemical cell, indicating that this compound is a magnesium ion conductor.

In recent years, due to the several advantages of permanent magnet synchronous generator (PMSG), the number of wind farms utilizing this technology has been significantly grown. The determination of the failure mechanism in these devices is the major challenge which has been addressed in many studies. Particularly, response to grid code compliance by wind power in the voltage drop situation needs to be comprehensively analyzed. In this paper, a small signal model of a PMSG-based wind turbine for low voltage ride-through (LVRT) and suitable for stability and artificial intelligent studies is presented. Accordingly, the generator side converter controls the dc-link voltage, and the maximum power point tracking is performed by the grid side converter. Given the proposed model, the speed of the simulation for stability analysis studies can be significantly increased by intelligent methods. Furthermore, the simplified approach can be achieved for calculating the optimal coefficients of the... [more]

In many countries around the world heating (and cooling) has been and will remain the biggest energy sector, but it is still widely dominated by fossil energy sources today. Wastewater as a source of renewable energy contains large amounts of heat and due to its place-bound localization in urban sewer systems it is usually also situated in very close distance to potential heat consumers. However, one has to keep in mind that heat extraction from wastewater might have undesired impacts on temperature-sensitive treatment processes in the related wastewater treatment plant (WWTP). To assess the potential impact of in-sewer heat recovery on inflow temperature, two different approaches are available today: a simple (but less significant) alligation alternate, or very accurate (but less practical) mathematical models. To close the gap between practicability and significance this article introduces a novel approach to pre-assess the suitability of in-sewer heat recovery sites based on little... [more]

The evaluation and renovation of existing building envelope has important practical significance for energy conservation and emission reduction in the field of architecture. With the development of digital cities, 3D models with rich temperature information can realize the comprehensive and accurate detection and evaluation of the existing building envelope. However, the 3D model reconstructed from thermal infrared images has only relative temperature distribution and no temperature value of each location, so it is impossible to quantify the extent of the defect from it. To solve this issue, this paper develops a method to establish a 3D point cloud model with temperature information at selected points. The proposed 3D model is generated based on the thermal infrared images acquired by an unmanned aerial vehicle (UAV) equipped with an infrared camera. In the generated 3D thermal infrared model, we can not only get the relative temperature distribution of the building’s full envelope st... [more]

In this paper, a proton exchange membrane fuel cell (PEMFC) is implemented as a grid-connected electrical generator that uses hydrogen gas as fuel and air as an oxidant to produce electricity through electrochemical reactions. Analysis demonstrated that the performance of the PEMFC greatly depends on the rate of fuel supply and air supply pressure. Critical fuel and air supply pressures of the PEMFC are analysed to test its feasibility for the grid connection. Air and fuel supply pressures are varied to observe the effects on the PEMFC characteristics, efficiency, fuel supply, and air consumption over time. The PEMFC model is then implemented into an electrical power system with the aid of power electronics applications. Detailed mathematical modelling of the PEMFC is discussed with justification. The PEMFC functions as an electrical generator that is connected to the local grid through a power converter and a transformer. Modulation of the converter is controlled by means of a proport... [more]

Driver behavior is one of the most relevant factors affecting road safety. Many traffic situations require a driver to be able to recognize possible danger. In numerous works, aggressive driving is understood as unsafe and as a hazard entailing the risk of potential crashes. However, traffic safety is not the only thing affected by a vehicle operator’s driving style. A driver’s behavior also impacts the operating costs of a vehicle and the emission of environmental air pollutants. This is confirmed by numerous works devoted to the examination of the effect of driving style on fuel economy and air pollution. The objective of this study was to investigate the influence of aggressive driving on fuel consumption and emission of air pollutants. The simulation was carried out based on real velocity profiles collected in real-world tests under urban and motorway driving conditions. The results of simulations confirm that an aggressive driving style causes a significant increase in both fuel c... [more]

Superhigh organic sulfur(SHOS) coals have currently attracted great attention due to their typical depositional environments and formation history as well as their great negative impact on the ecosystem. This study investigated the geochemistry of the No. 11coalof the Late Carboniferous Taiyuan Formation from the Sangshuping coalmine, Hancheng miningarea, Weibei coalfield, Shaanxi, North China. The No. 11 coal is a high-sulfur coal with a large proportion of organic sulfur content (3.7 to 5.5%, avg. 4.4%) and belongs to typical SHOS coal. The high sulfur content in the Sangshuping coal mine has been mainly caused by the combined influences of seawater and hydrothermal fluids. The SHOS in No. 11 coal was formed in the Fe-poor and S-rich high-marine influenced occlusive environment. During the late coalification stage, a high proportion of pyritic sulfur was formed due to sufficient Fe supply from the Fe−S-rich epigenetic hydrothermal fluids. The No. 11 SHOS coal is enriched in Li−Ga−Zr−... [more]

A virtual power plant (VPP) can be defined as the integration of decentralized units into one centralized control system. A VPP consists of generation sources and energy storage units. In this article, based on real measurements, the charging and discharging characteristics of the battery energy storage system (BESS) were determined, which represents a key element of the experimental virtual power plant operating in the power system in Poland. The characteristics were determined using synchronous measurements of the power of charge and discharge of the storage and the state of charge (SoC). The analyzed private network also includes a hydroelectric power plant (HPP) and loads. The article also examines the impact of charging and discharging characteristics of the BESS on its operation, analyzing the behavior of the storage unit for the given operation plans. The last element of the analysis is to control the power flow in the private network. The operation of the VPP for the given scen... [more]

In recent years, penetration of renewable energy resources into the power grid has increased significantly. Wind, as a renewable, clean, and abundantly available source of energy, has an important share in the energy mix. However, increasing the penetration of wind power in the power grid can adversely affect the power quality and introduce new operational challenges. This paper discusses issues related to the integration of wind farms in the power system, such as maximum power point tracking, fault ride-through capabilities, interarea and subsynchronous oscillations, and voltage flicker, and provides a review of the existing control strategies to address these issues in Types I, II, III, and IV wind turbines. This paper also identifies challenges and opportunities ahead.

This paper presents a static network equivalent model for Korean power systems. The proposed equivalent model preserves the overall transmission network characteristics focusing on power flows among areas in Korean power systems. For developing the model, a power transfer distribution factor (PTDF)-based k-means++ algorithm was used to cluster the bus groups in which similar PTDF characteristics were identified. For the reduction process, the bus groups were replaced by a single bus with a generator or load, and an equivalent transmission line was determined to maintain power flows in the original system model. Appropriate voltage levels were selected, and compensation for real power line losses was made for the correct representation. A Korean power system with more than 1600 buses was reduced to a 38-bus system with 13 generators, 25 loads, and 74 transmission lines. The effectiveness of the developed equivalent model was evaluated by performing power flow simulations and comparisons... [more]

Rubber involving magnetic compound fluid (MCF) and TiO2 is effective in dye-sensitized solar cells (DSSCs) to create large efficacy. Wearable and portable solar cells made of MCF rubber are the most desirable as soft materials in robots or flexible devices, and they are further desirable because they have self-generated power and power supply with sensing. Therefore, we investigated the effect of TiO2 catalysts on the photovoltaic effect of MCF rubber DSSCs under large tension and compression. The characteristics of the built-in electricity and photoelectricity were clarified experimentally. The experimental results were explained by a chemical−photovoltaic mechanism involving the behavior of dye, electrolytes, water, and rubber molecules, as well as a catalytic effect of the metal component of the MCF on Ni, Fe3O4, and TiO2. Once we are able to produce solar cells that have large tension and compression, the present experimental results and the model of the chemical−photovoltaic mecha... [more]

In this paper, a “general equilibrium” (GE) model was developed for the allocation of exhaustible natural resources to examine the impact of different extraction scenarios on intergenerational economic welfare. A stylized GE model was applied to Israel’s natural gas (NG) market to evaluate economic indicators resulting from NG-extraction scenarios: a baseline scenario based on current policy in the NG sector, a conservative scenario based on a lower extraction rate, and an intensive scenario based on a faster extraction rate. The impact of various resource income-allocation strategies on intergenerational economic welfare was examined through the mechanism of a “sovereign wealth fund” (SWF). The results indicate that a higher NG-extraction rate combined with an appropriate investment strategy for NG profits is preferable from an economic perspective compared to a conservative rate. Investment of the government take from the NG market in research and development (R&D) of renewable elect... [more]

This study proposes an improved design for a typical sludge continuous feeding drying system connected with three air-source heat pumps. The system’s performance was further improved using air-deflectors on the drying chamber’s internal sidewalls, enhancing the heat and mass transfer between the conveyor sludge and circulating airflow. In this study, numerical analysis was performed to elucidate the deflector designs on the airflow field and thermal temperature field distributions in the drying chamber. The specific moisture extraction rate (SMER) value was quantified to evaluate the system’s overall improvement during experiments. With a suitable deflector design, the average percent water content in sludge could be further reduced to 22.2% with drying time of 18.3 h, and the SMER value could be enhanced from 1.38 kg/kWh to as high as 1.83 kg/kWh with an increment of 32.44%. Moreover, to prevent overloading and frequent shutdown of the compressors, an auxiliary cooling subsystem was d... [more]

The green alga Botryococcus braunii produces abundant hydrocarbons, in the form of drop-in biodiesel, which promoted interest in the species as a renewable fuel. However, despite the observation of dense populations in the wild, Botryococcus grows very slowly in culture, severely limiting its potential for development as a bioresource. Undertaking a biodiscovery program, we found new strains of Botryococcus in locations ranging from tropical to temperate Australia and from both fresh and brackish waters. As part of the ecophysiological characterisation of this new biodiversity, lipid and pigment compositions were studied for six new strains from six different locations. The strains were inoculated in either freshwater or brackish (salinity of 4)-based medium and maintained over 150 days. The growth of cultures was studied continuously, while lipid and pigment composition were analysed at final harvest on day 150. No significant differences in growth rate between fresh and brackish medi... [more]