Due to the complex operation conditions in a power transformer, an oil-impregnated pressboard (OIP) simultaneously suffers from thermal, electrical, and mechanical stress. Since most research studies have paid much attention to thermal or electrical aging of OIPs, this paper analyzes the effects of long-term mechanical vibrations on cellulose degradation in OIPs under simultaneous multi-stress. The aging experiments were firstly conducted at 130 °C, with a DC electric voltage of +6 kV, vibration amplitude of 10−50 μm, and vibration frequency of 100−300 Hz. The finite element analysis (FEA) of the pressboard vibration model was then performed on Abaqus to investigate the time−frequency domain characteristic parameters of compressive stress on the pressboard under varied vibration frequencies and amplitudes. The FEA results reveal that compressive stress on the pressboard in a multi-stress aging experiment coincided with the axial compressive stress on the insulation spacers in an SZ-500... [more]

A huge amount of industrial waste will be generated during the industrialization process and their harmless disposal has always been a headache for reducing carbon emissions. In this study, the combustion behaviors and thermal kinetics of four typical industrial polymeric wastes including rubber, leather, plastic and cloth, were systematically studied by using a Thermogravimetric Analysis. The gas emission and structural evolution was comprehensively analyzed using TG-FTIR, 2D-PCIS, ICP and TEM. The results show that the combustibility of leather and cloth are better than the other two samples, while the rubber and plastic have a wider combustion temperature range for higher content of C-H bonds and, the intermediate oxidation process and the stubborn cracking process of C=C bonds. The surface reaction was considered to be the main reaction of rubber and plastic (pre-exponential factor less than 10−9), while both leather and cloth went through a complex procedure during multiple decomp... [more]

The paper presents the results of FEM 2D computational studies of a three-phase Direct Current Excited Flux Switching Machine (DCEFSM) electric motor with 15 rotor teeth and 36 stator teeth. The aim of the research was to minimize the cogging torque of the machine by changing the geometry of the rotor teeth and the size of the air gap between the stator and the rotor, with the operating torques unchanged. Computational studies were carried out on the influence of the width of the rotor teeth, the radius of the rounding of their corners, and the size of the air gap on the cogging torque and machine operating torques. The results of the calculations made it possible to select the dimensions of the rotor and the air gap in such a way that the maximum cogging torque was reduced more than six-fold, with the machine operating torques being unchanged. The calculations also showed that it is not possible to increase the value of the operational torques by further changes in the geometry of the... [more]

This paper analysed operational CO2 emissions from electricity grid interaction in photovoltaic prosumer dwellings in South Wales, UK. Operational CO2 emissions were quantified in four prosumer dwellings aiming to analyse (1) the differences in the result when time-varying data and static emission factors are used, and (2) the association of load-matching indicators to the results. Electricity balance data were obtained through monitoring (April 2020 to March 2021), and three sources for the grid’s CO2 intensity were considered: (1) UK nationwide average time-varying values (UK), (2) South Wales (SW) average time-varying values and (3) the UK Government’s official CO2 emissions factor (EF) for the study period. UK and SW grid CO2 intensity were obtained as dynamic data flows in a 30 min resolution, whereas EF was a year constant. Gross CO2 emissions calculated using SW data reached the highest emissions results: between 67.5% and 69.3% higher than the results obtained using the UK time... [more]

This article introduces a three-phase capacitor clamped inverter with inherent boost capability by relocating the filter components from the AC side to the configuration’s midpoint. This topology has several distinguishing characteristics, including: (a) low component count; (b) high DC-AC gain; (c) decreased capacitor voltage stresses; (d) improved power quality (extremely low voltage and current THDs) without the use of an AC-side filter; and (e) decreased voltage stresses on power semiconductor devices. Simulations were carried out on the MATLAB Simulink platform, and results under steady-state conditions, load and reference change conditions, and phase sequence change conditions, along with THD profiles, are presented. This inverter’s performance was compared to that of similar converters with intrinsic gain. A 1200 W experimental prototype was built to demonstrate the system’s feasibility and benefits. When compared to existing topologies, simulation and experimental results indic... [more]

Simulations of emergency states and tests of resistance of electrical devices to emergencies are performed in specialized high-power laboratories, the so-called short-circuit laboratories. For most electrical power devices, such measurements are required by international standards. The basic equipment of short-circuit testing laboratories consists of current transformers for measuring short-circuit currents. These transformers should not only enable the accurate conversion of sinusoidal currents—which is typical for conventional current transformers, but also asymmetrical short-circuit currents containing an aperiodic component, which classic current transformers cannot reproduce. Therefore, manufacturers and designers try to meet the market demands and design these special class 0.2 current transformers. To meet the high technical requirements, the field-circuit method with three-dimensional space−time analysis of electromagnetic fields was used during design, considering physical phe... [more]

A tunnel boring machine (TBM) is an important large-scale engineering machine, which is widely applied in tunnel construction. Precise cutterhead torque prediction plays an essential role in the cost estimation of energy consumption and safety operation in the tunneling process, since it directly influences the adaptable adjustment of excavation parameters. Complicated and variable geological conditions, leading to operational and status parameters of the TBM, usually exhibit some spatio-temporally varying characteristic, which poses a serious challenge to conventional data-based methods for dynamic cutterhead torque prediction. In this study, a novel hybrid transfer learning framework, namely TRLS-SVR, is proposed to transfer knowledge from a historical dataset that may contain multiple working patterns and alleviate fresh data noise interference when addressing dynamic cutterhead torque prediction issues. Compared with conventional data-driven algorithms, TRLS-SVR considers long-ago... [more]

The accurate estimation of rotor position and speed before flying restart is of great significance to improve the operation reliability of permanent magnet synchronous motor systems. The traditional multizero vector short-circuit method can improve the estimation accuracy of speed and rotor position, but the increased number of short-circuits reduces the electromagnetic torque response speed after the power supply recovers. In order to accurately estimate the initial speed and rotor position before the flying restart and effectively improve the electromagnetic torque response speed, a shoot-through zero vector short-circuit method based on quasi-Z-source inverter (qZSI) is proposed. This method breaks the limitation of regulating DC link voltage under the normal operation of the motor in the conventional methods, and puts forward a new idea of advancing the regulation of the DC link voltage to the stage of abnormal operation before the motor restarts. By designing the insertion mode of... [more]

Wellbore instability is one of the main problems of the oil industry, causing high costs in the drilling operation. Knowing about the mechanical properties of involved formations and in-situ stresses is a privilege gained by determining an appropriate mud weight window (MWW). To this aim, a three-dimensional (3D) finite-element model was simulated in ABAQUS to analyze in-situ stresses and determine the MWW in the drilling operation of wellbore-D in the Azar oilfield. The results from the 3D finite model revealed that the Azar oilfield is structurally under the impact of a complex tectonic system dominated by two reverse faults with a configuration of σH > σh > σv across the Sarvak Formation. The amount of vertical, minimum, and maximum horizontal stresses was 90.15, 90.15, and 94.66 MPa, respectively, at a depth of 4 km. Besides, the amount of pore pressure and its gradient was 46 MPa and 11.5 MPa/km, respectively. From drilling wellbore-D in the direction of the maximum horizontal str... [more]

A power transformer is one of the most critical and expensive assets in electric power systems. Failure of a power transformer would not only result in a downtime to the entire transmission and distribution networks but may also cause personnel and environmental hazards due to oil leak and fire. Hence, to enhance a transformer’s reliability and extend its lifespan, a cost-effective and reliable condition monitoring technique should be adopted from day one of its installation. This will help detect incipient faults, extend a transformer’s operational life, and avoid potential consequences. With the global trend to establish digital substation automation systems, transformer online condition monitoring has been given much attention by utilities and researchers alike. Several online and offline condition monitoring techniques have been recently proposed for oil-immersed power transformers. This paper is aimed at providing a state-of-the-art review for the various condition monitoring tech... [more]

Installations of an Energy Storage System (ESS) with various functions such as power stabilization of renewable energy, demand management, and frequency adjustment are increasing. In particular, ESS for demand management is being established for high-voltage customers (300 KVA−1000 KVA) who have placed an Auto Section Switch (ASS) at the connection point within the distribution system. However, a power outage may occur in the Power Receiving System (PRS) when a short-circuit fault due to insulation breakdown occurs at the ESS DC side. The reason for this breakdown is that the fault current is reduced by transformer impedance, and the ASS is opened before the DC power fuse. Therefore, using the Graphic Solution Method (GSM), this paper presents an operation algorithm for protection coordination that isolates the fault section by first operating the DC power fuse with a small fault current. Furthermore, fault analysis modeling for a PRS composed of a switchgear section, a main distributi... [more]

Various metrological aspects for the correct measurements of electrical energy that is consumed by energy-saving (mainly LED) single phase loads are discussed in this paper. One of the most important problems presented here concerns the question of how strong distortions of the current waveform, introduced by typical LED lighting, affects the operation of electronic energy meters. Measurement results for the energy consumption of different LED lamps used in households in various conditions, alongside comparative results that were obtained by electronic and electromechanical energy meters, were also offered and the appropriate conclusions were then drawn.

This work formulates a stochastic dynamic programming (SDP) model that incorporates seasonal electricity prices and can handle a constraint on power yield, which is assumed to be satisfied at any time it is possible, thus allowing for an analysis of their impacts on the operational performances of cascaded reservoirs. The model is applied to the Lancang Cascade, specifically its two largest reservoirs, Xiaowan and Nuozhadu. The results show that increasing the power yield of the cascade will reduce energy production unfavorably but will impact water spillage favorably, with a power yield of 2000 MW and with a 91% reliability suggested as being a satisfactory operational target. The case study also suggests that using seasonal electricity prices makes the power generation very unstable during weeks 12−20, which is a period of time that is critical to transferring from dry to flooding seasons.

The large fluctuation of net torque and the existence of negative torque on the crank output shaft of the beam pumping unit are the decisive factors leading to its low efficiency and high energy consumption. The conventional pumping unit CYJ10-4.2-53HF was selected as the study object on the basis of the fixed shaft secondary balance principle and the positive torque modulation scheme was first proposed according to the following secondary balance principle based on the linkage. The kinematics analysis of the suspension point and the secondary incremental velocity mechanism were carried out using the theory of rigid body plane kinematics. The force analysis of each moving part of the pumping unit was carried out, the net torque expression of the crank output shaft was obtained, and an example calculation was performed. The positive torque beam pumping unit was developed and tested in a field test. The tests showed that the positive torque beam pumping unit was able to fully realize pos... [more]

The field data from an integrated CO2 refrigeration system installed in a supermarket located north of the capital of Lisbon was analyzed. The goal was to demonstrate the effect and performance of multi-ejectors on a refrigeration system operating in a warm climate. The measurement results for the system with and without activating ejectors were compared. It was observed that the system with a multi-ejector operation had considerable performance superiority. The ejectors improved the cooling capacity of the medium temperature stage of the system by 17.4%. The system with active ejectors had 7.5% less total power consumption compared to the ejector off mode of the same system.

In an energy harvesting wireless sensor node (EHWSN), balance of energy harvested and consumption using dynamic energy management to achieve the goal of perpetual operation is one of the most important research topics. In this study, a novel fuzzy Q-learning (FQL)-based dynamic energy management (FQLDEM) is proposed in adapting its policy to the time varying environment, regarding both the harvested energy and the energy consumption of the WSN. The FQLDEM applies Q-learning to train, evaluate, and update the fuzzy rule base and then uses the fuzzy inference system (FIS) for determining the working duty cycle of the sensor of the EHWSN. Through the interaction with the energy harvesting environment, the learning agent of the FQL will be able to find the appropriate fuzzy rules in adapting the working duty cycle for the goal of energy neutrality such that the objective of perpetual operation of the EHWSN can be achieved. Experimental results show that the FQLDEM can maintain the battery... [more]

Thermodynamic, exergetic and thermoeconomic analyses were performed on two types of double-effect LiBr−water absorption refrigeration systems (ARS) for use with a 5-kW high-temperature proton exchange membrane fuel cell (HT-PEMFC) as a heat source. Proper temperatures of the high-pressure generator, combined generator and condenser, condenser, absorber and evaporator were determined to meet the requirements of constant cooling demands for data center operations. The heat balance of the combined unit of generator and condenser in the industrial double-effect LiBr-water ARS is important for determining the flow rate of the primary vapor refrigerant from the high-pressure generator. The industrial double-effect ARS system, whose analysis has not been studied analytically, outperformed the series double-effect system and provided 6.5 kW of cooling capacity with a coefficient of performance of 0.99. The unit cost of chilled water estimated by the modified productive structure analysis (MOPS... [more]

The paper presents a method for assessing operation processes for Fire Alarm Systems (FAS) applied in civil structures, based on use analysis. Individual FAS devices include components with varying ‘lifetimes’ and damage intensities λ. This is because these elements are operated in different internal and external environments. Probability distributions with various damage λ and recovery µ intensity values must, hence, be taken into account for the FAS operation process and to determine the R(t) reliability. The life cycle of elements comprising a FAS can be divided into three distinguishing time periods. The first is the so-called ‘childhood’. The second, the longest, is characterized by damage intensity λ = const, and the third period is where FAS is unfit more frequently. Based on knowledge of actual FAS operation process data, it is possible to determine damage λ and recovery µ intensity parameters. Such data can be employed to determine FAS reliability parameters within the present... [more]

The aim of this article is to identify the benefits perceived by individual recipients that are achieved by consumer energy suppliers on the market, through multilateral trade cooperation, and to define the structure of these benefits according to the declared readiness of recipients to cooperate with the suppliers. The results of the analysis of the available literature on the subject indicate that there is a cognitive and research gap in relation to the perceived benefits achieved by the suppliers through joint marketing activities. The benefits are not being analyzed; especially from the perspective of individual recipients’ readiness for this cooperation. This gap is noticeable not only in relation to the energy market, but also in other areas of the consumer market. In an effort to reduce the identified gap, an online survey was conducted among 1196 adult individual energy recipients in Poland. The primary data collected was subjected to quantitative analysis using the following r... [more]

This paper analyzes the electromagnetic torque (EMT) fluctuation characteristics in synchronous generators under rotor interturn short-circuit (DRISC) fault. The novelty of this paper is that the DRISC fault is proposed based on the intermittent interturn short circuit existing in the actual operation and compared with the static rotor interturn short-circuit (SRISC) fault. In the work, by studying the influence of DRISC with different positions and different short-circuit degrees, the fluctuation characteristic of the EMT is analyzed and verified. The results show that when the DRISC5% fails, the location is in slot 3, the amplitude of first harmonic decreases by 7.2%, second harmonic amplitude increases by 33.4%, third harmonic decreases by 4.3%, and fourth harmonic increases by 26.8%. As the degree increased and positioned away from the large tooth of the DRISC, the overall EMT amplitude and reverse pulse increased, first and third harmonics decreased, and second and fourth harmonic... [more]

Smart transformers are considered a crucial part of future smart grids as they will operate as the energy router and be able to control the power flows from and to the microgrids since they are placed in the border. A multi-port transformer can integrate different energy resources, loads and energy storage systems, optimizing the power flows between these elements. Combining both concepts, a multi-port smart transformer is obtained that is able to integrate efficiently distributed and renewable energy resources, electric vehicle chargers, prosumers and energy storage in both AC and DC microgrids. Nevertheless, the operation of these transformers, composed of several modules connected in series to the high-voltage grid is not easy, mainly due to the different power consumed or generated by each module. In this paper this issue is analyzed and different operation strategies for coordinating the series-connected modules at the input side are studied by simulation. The paper will expose ho... [more]

One of the crucial steps for a successful integration of electric bus fleets into the existing electric power systems is the active and intelligent usage of their flexibility. This is important not only for reducing the eventual negative effects on the power grid but also for reducing energy and infrastructure costs. The first step in the optimal usage of flexibility is its quantification, which allows the maximum provision of flexibility without any negative effects for the fleet operation. This paper explores the available flexibility of large-scale electric bus fleets with a concept of centralized and unidirectional depot charging. An assessment of available positive and negative flexibility was conducted based on the data from two real bus depots in the city of Hamburg, Germany. The analysis shows the biggest flexibility potential was in the period from 16:00 h to 24:00 h, and the smallest one was in the periods from 08:00 h to 16:00 h, as well as from 02:00 h to 08:00 h. The paper... [more]

Voltages of series-connected energy storage cells, such as electric double-layer capacitors (EDLCs) and lithium-ion batteries, need to be equalized to ensure years of safe operation. However, to this end, a voltage equalizer is necessary in addition to a charger, increasing the system complexity and cost. This paper proposes a family of transformerless single-switch integrated chargers that merge a charger and equalizer into a single unit, achieving a simplified system and circuit. Proposed integrated chargers are derived by stacking multiple conventional pulse width modulation (PWM) converters, such as a superbuck converter, that contain two inductors and one energy transfer capacitor. Detailed operation analyses, including an investigation on the impact of component tolerance on voltage equalization performance, are also performed. Experimental charging tests using a 12-W prototype were performed for four EDLC cells. All cells were charged with eliminating voltage imbalance and demon... [more]

In an effort to improve the energy economics of hydraulic systems, attention should be paid to reducing power losses in two main entities, energy converting components, and energy controlling and conveying components. Achieving the former requires utilizing components’ most energy efficient operating range. The energy converting efficiency of a pump, which is the primary energy converter in a hydraulic system, is determined by several operational factors. Of these, only pressure and rotational speed are normally considered, but also the fluid temperature and derived capacity with variable displacement pumps have a major effect on the efficiency. Omitting these factors may lead to running the pump outside its most efficient operation range and cause high energy losses. Operating the pump in its optimal region calls, however, for detailed knowledge of its performance characteristics, which are not generally made public by the pump manufacturers. This study presents the performance measur... [more]

Excessive water inflow in a mine poses a great threat to its operation, especially in the case of a salt mine. In 1992, a rapid outflow of water occurred in the Mina traverse in the Wieliczka Salt Mine, and a number of investigations were undertaken to assess the causes of the outflow and the condition of the rock mass, including the gravity and microgravity surveys discussed in this paper. The first of these was to investigate the rock mass with respect to its geological, hydrogeological properties and mining. The aim of study was to monitor the changes in the rock mass density and the impact of these changes on the subsidence of the ground surface. The surveys provided information on the geological structure of the study area and helped to identify possible routes for water migration. The first data confirmed density changes in the shallow parts of the rock mass, manifested by subsidence of the land surface. However, the subsequent measurements failed to show any significant density... [more]