Fault DiagnosisMethod of Energy Storage Unit of Circuit Breakers Based on EWT-ISSA-BP

Aiming at the problem of energy storage unit failure in the spring operating mechanism of low voltage circuit breakers(LVCBs).A fault diagnosis algorithm based on an improved Sparrow Search Algorithm(ISSA)optimized Backpropagation Neural Network(BPNN)is proposed to improve the operational safety of LVCB.Taking the 1.5kV/4000A/75kA LVCB as an example.According to the current operating characteristics of the energy storage motor,fault characteristics are extracted based on Empirical Wavelet Transform(EWT).Traditional BPNN has problems such as difficulty adjusting network weights and thresholds,being sensitive to initial weights,and quickly falling into local optimal solutions.The Sparrow Search Algorithm(SSA)with self-adjusting weight factors combined with bidirectional mutations is added to optimize the selection of BPNN hyperparameters.The results show that the ISSA-BPNN can accurately and quickly distinguish six conditions of motor voltage reduction:motor voltage increase,motor voltage decrease,energy storage spring stuck,transmission gear stuck,regular state and energy storage spring not locked.It is suitable for fault diagnosis and detection of the energy storage part of LVCB.

Analysis of a Novel Mechanically Adjusted Variable Flux Permanent Magnet Homopolar Inductor Machine with Rotating Magnetic Poles for Flywheel Energy Storage System

Permanent magnet homopolar inductor machine(PMHIM) has attracted much attention in the field of flywheel energy storage system(FESS) due to its merits of simple structure,brushless excitation, and rotor flywheel integration. However, the air-gap flux generated by the PM cannot be adjusted, which would cause large electromagnetic losses in the standby operation state of FESS. To solve this problem, a novel mechanically adjusted variable flux permanent magnet homopolar inductor machine with rotating magnetic poles(RMP-PMHIM) is proposed in this paper. The permanent magnet poles are rotated by an auxiliary rotating device and the purpose of changing the air-gap flux is achieved. First, the structure and operation principle of the proposed RMP-PMHIM are explained. Second,the flux weakening principle of the RMP-PMHIM is analyzed and the equivalent magnetic circuit models under different flux weakening states are built. Third, the parameters of the PM and its fixed structure are optimized to obtain the good electromagnetic performance. Fourth, the electromagnetic performance, including the air-gap flux density, back-EMF, flux weakening ability, loss, etc. of the proposed RMP-PMHIM are investigated and compared. Compared with the non-rotating state of the PM of RPM-PMHIM, the air-gap flux density amplitude can be weakened by 99.95% when the PM rotation angle is 90 degrees, and the no-load core loss can be suppressed by 99.98%,which shows that the proposed RPM-PMHIM is a good candidate for the application of FESS.

Role of Energy Storage on Distribution Transformer Loading in Low Voltage Distribution Network

Energy storage (ES) is a form of media that store one form of energy to be utilized at another time. Importance of ES is comprehended while intermittent nature of renewable energy (RE) generation increases and integration into the grid becomes viable in terms of economics and environment. However, technical analysis should be carried out before large scale integration into the grid. Some utilities experienced in Europe and expressed concern about issues in integrating large scale renewable energy in the areas of harmonics, voltage regulation, network protection and islanding. In Australia, distribution network (DN) is not robust compared to the European grid;moreover loads are largely distributed over large geographical areas. Installation of RE such as roof top solar photovoltaic (PV) is increasing in Australia which also boosted by the governments incentives to the individual owners. It is therefore obvious that large scale PV integration into the Australian grid is imminent. The intermittent characteristic of solar PV is expected to have greater impacts on DN in Australia compared to the DN in Europe. Therefore this paper investigated the impacts of solar PV on low voltage (LV) DN where loads connected through distribution transformer (DT) and finally further investigation was conducted with the deployment of ES into the respective load centers. It was found that storage reduced the overall peak load condition on the DT, and also reduced the energy fluctuation in the DN. It was also found that storage improved the voltage regulation on the LV side of DT and stabilized node voltage.

Studying the variable energy band structure for energy storage materials in charge/discharge process

So far,a clear understanding about the relationship of variable energy band structure with the corresponding charge-discharge process of energy storage materials is still lacking.Here,using optical spectroscopy(red-green-blue(RGB)value,reflectivity,transmittance,UV-vis,XPS,UPS)to studyα-Co(OH)_(2) electrode working in KOH electrolyte as the research object,we provide direct experimental evidence that:(1)The intercalation of OH-ions will reduce the valence/conduction band(VB and CB)and band gap energy(Eg)values;(2)The deintercalation of OH-ions corresponds with the reversion of VB,CB and E_(g) to the initial values;(3)The color of Co(OH)_(2) electrode also exhibit regular variations in RGB value during the charge-discharge process.

PV-based virtual synchronous generator with variable inertia to enhance power system transient stability utilizing the energy storage system

The Photovoltaic(PV)plants are significantly different from the conventional synchronous generators in terms of physical and electrical characteristics,as it connects to the power grid through the voltage-source converters.High penetration PV in power system will bring several critical challenges to the safe operation of power grid including transient stability.To address this problem,the paper proposes a control strategy to help the PVs work like a synchronous generator with variable inertia by energy storage system(ESS).First,the overall control strategy of the PV-based virtual synchronous generator(PV-VSG)is illustrated.Then the control strategies for the variable inertia of the PV-VSG are designed to attenuate the transient energy of the power system after the fault.Simulation results of a simple power system show that the PV-VSG could utilize the energy preserved in the ESS to balance the transient energy variation of power grid after fault and improve the transient stability of the power system.

Rationally exfoliating chitin into 2D hierarchical porous carbon nanosheets for high-rate energy storage

Two-dimensional(2D)carbon nanomaterials with hierarchical porous structure and heteroatoms doping are highly desirable in the fields of energy storage because of their rich active surface and open ion diffusion channels.However,the scalable preparation of carbon materials simultaneously possessing ultrathin 2D feature and hierarchical pores remains a considerable challenge.Herein,a facile one-step method to massively fabricate 2D porous chitin nanosheets(coded as PCNs)via a phytic acid assisted top-down exfoliation of bulk chitin under hydrothermal treatment was presented.Subsequently,2D carbon nanosheets with extra-thin thickness(3.6 nm),well-defined hierarchical porosity,high specific surface area(855 m2·g^-1),as well as abundant self-doped heteroatoms(N,O,P)were fabricated by carbonizing the PCNs,and was named as HPCNs.The as-obtained HPCNs demonstrated remarkable electrochemical performance as electrode material for supercapacitors.The symmetric supercapacitors(SSCs)based on HPCNs exhibited a high specific capacitance of 79 F·g^-1(316 F·g^-1 for single electrode)in 6 M KOH aqueous electrolyte solution,as well as a remarkable energy density of 23.8 W·h·kg^-1 by using 1 M Li2SO4 as electrolyte.It is also demonstrated that HPCNs/PCNs hybrid dispersions can be used as inks to fabricate conductive films and energy devices with high strength and superior flexibility.This work paves a new avenue for the economical and large-scale synthesis of 2D hierarchically porous carbon materials for energy storage related applications.

Control Strategy of Wind Turbine Based on Permanent Magnet Synchronous Generator and Energy Storage for Stand-Alone Systems

This paper investigates a variable speed wind turbine based on permanent magnet synchronous generator and a full-scale power converter in a stand-alone system.An energy storage system(ESS)including battery and fuel cell-electrolyzer combination is connected to the DC link of the full-scale power converter through the power electronics interface.Wind is the primary power source of the system,the battery and FC-electrolyzer combination is used as a backup and a long-term storage system to provide or absorb power in the stand-alone system,respectively.In this paper,a control strategy is proposed for the operation of this variable speed wind turbine in a stand-alone system,where the generator-side converter and the ESS operate together to meet the demand of the loads.This control strategy is competent for supporting the variation of the loads or wind speed and limiting the DC-link voltage of the full-scale power converter in a small range.A simulation model of a variable speed wind turbine in a stand-alone system is developed using the simulation tool of PSCAD/EMTDC.The dynamic performance of the stand-alone wind turbine system and the proposed control strategy is assessed and emphasized with the simulation results.

Review on thermal performance of phase change energy storage building envelope

Improving the thermal performance of building envelope is an important way to save building energy consumption. The phase change energy storage building envelope is helpful to effective use of re-newable energy, reducing building operational energy consumption, increasing building thermal com-fort, and reducing environment pollution and greenhouse gas emission. This paper presents the con-cept of ideal energy-saving building envelope, which is used to guide the building envelope material selection and thermal performance design. This paper reviews some available researches on phase change building material and phase change energy storage building envelope. At last, this paper pre-sents some current problems needed further research.

Applications of membrane distillation technology in energy transformation process-basis and prospect

Membrane distillation technology is a new type of efficient separation technology that combines traditional distillation technology and membrane separation technology. In the study, applications of membrane distillation technology in thermal engineering and refrigerating engineering with typical energy transformation process were presented. Desorption and regeneration process of saline solution by vacuum membrane distillation was proposed on the basis of the concentration and separation properties of membrane distillation. Membrane distillation technology could be used in lithium bromide absorption refrigeration system, energy storage system, and the regeneration process of liquid desiccant solution in temperature-humidity independent control air-conditioning system. The aim of the applications was to use the low-grade energy such as waste heat, solar energy and geothermal energy adequately and to improve the available temperature difference of heat source. According to latent heat transfer and thermal conduction across the membrane in direct contact membrane distillation process, a novel membrane heat exchanger with both heat transfer and mass transfer processes was proposed. The heat exchanger could be used as the solution heat exchanger of lithium bromide absorption refrigeration system and as the special heat exchanger that recovered heat and pure water simultaneously. Some feasible process flows about the applications of membrane distillation technology to energy transformation process were listed and analyzed. Finally, future research emphases were indicated.

Present status of pumped hydro storage operations to mitigate renewable energy fluctuations in Japan

This paper focuses on pumped hydro energy storage(PHES)plants’current operations after electricity system reforms and variable renewable energy(VRE)installations in Japan.PHES plants have historically been developed to create electricity demand at night in order to operate base load power plants,such as nuclear power plants,in stable conditions.Therefore,many PHES plants are located midway between nuclear power plants and large demand areas.However,all nuclear power plants had to–at least temporarily–shut down after the Great East Japan Earthquake followed by a nuclear accident at Fukushima Daiichi in 2011,and renewable energy power plants have been deployed rapidly after the introduction of a feed-in-tariff(FIT)scheme.Therefore,PHES plants are being used to mitigate fluctuations of VRE,especially in areas where renewable energy has been significantly installed.The daily highest capacity ratio of PHES plants in Kyushu area has recorded three times higher than it in the other areas where the past operating mode is still conducted.But those operations on PHES plants are simply followed as a dispatch rule of the Organization for Crossregional Coordination of Transmission Operators(OCCTO),market-based operations have not been conducted enough yet.The market design shall be changed to harmonize VRE installation and PHES plants’operations are necessary to make the transition from the past operating mode of PHES plants across Japan.

Safety regulation of gel electrolytes in electrochemical energy storage devices

Electrochemical energy storage devices,such as lithium ion batteries(LIBs),supercapacitors and fuel cells,have been vigorously developed and widely researched in past decades.However,their safety issues have appealed immense attention.Gel electrolytes(GEs),with a special state in-between liquid and solid electrolytes,are considered as the most promising candidates in electrochemical energy storage because of their high safety and stability.This review summarized the recent progresses made in the application of GEs in the safety regulation of the electrochemical energy storage devices.Special attention was paid to the gel polymer electrolytes,the organic low molecule-mass GEs,as well as the fumed silica-based and siloxane-based GEs.Finally,the current challenges and future directions were proposed in terms of the development of GEs.

On the Implementation of the Method of Derivation of Lorentz Transformations Used by Einstein

The Lorentz transformations are the mathematical basis of Einstein’s theory of special relativity. We conduct a thorough examination of the method of derivation of the Lorentz transformations used by Einstein and identify the cause of the incorrect implementation of the method. The cause is related to the incorrect proof of the equality φ(v)=1for the unknown function φ(v)arising in the process of derivation of the Lorentz transformations. We develop proof of the equality φ(v)=1and eliminate the cause of the incorrect implementation of the method of derivation of the Lorentz transformations used by Einstein.

Numerical method and model for calculating thermal storage time for an annular tube with phase change material

For calculating the thermal storage time for an annular tube with phase change material （PCM）, a novel method is proposed. The method is suitable for either low-temperature PCM or high-temperature PCM whose initial temperature is near the melting point. The deviation fit is smaller than 8% when the time is below 2x104 s. Comparison between the predictions and the reported experimental data of thermal storage time at same conditions is investigated and good agreements have been got. Based on this method, the performance of the thermal storage unit and the role of natural convection are also investigated. Results show a linear relation between the maximum amount of stored heat and thermal storage time, and their ratio increases with the height of the thermal storage unit. As the thickness of the cavity increases, natural convection plays an increasingly important role in promoting the melting behavior of paraffin. When the thickness of the cavity is small, natural convection restrains the melting behavior of paraffin.

Classifying Electrolyte Solutions by Comparing Charge and Mass Transport

The conventional classification of electrolyte solutions as“strong”or“weak”accounts for their charge transport properties,but neglects their mass transport properties,and is not readily applicable to highly concentrated solutions.Here,we use the Onsager transport formalism in combination with linear response theory to attain a more general classification taking into account both charge and mass transport properties.To this end,we define a molar mass transport coefficientΛ_(mass),which is related to equilibrium center-of-mass fluctuations of the mobile ions and which is the masstransport analogue of the molar ionic conductivityΛ_(charge).Three classes of electrolyte solution are then distinguished:(i)“Strong electrolytes”with 4Λ_(mass)≈Λ_(charge);(ii)“weak charge transport electrolytes”withΛ_(charge)≪4Λ_(mass);and(iii)“weak mass transport electrolytes”with 4Λ_(mass)≪Λ_(charge).While classes(i)and(ii)encompass the classical“strong”and“weak”electrolytes,respectively,many highly concentrated electrolytes fall into class(iii)and thus exhibit transport properties clearly distinct from classical strong and weak electrolytes.

Hydrogen storage properties of MgH2 co-catalyzed by LaH3 and NbH

To improve the hydrogen storage properties of Mg-based alloys, a composite material of MgH_2 + 10wt%LaH_3 + 10wt%NbH was prepared by a mechanical milling method. The composite exhibited favorable hydrogen desorption properties, releasing 0.67wt% H2 within 20 min at 548 K, which was ascribed to the co-catalytic effect of LaH_3 and NbH upon dehydriding of MgH_2. By contrast, pure MgH_2, an MgH_2 + 20wt%LaH_3 composite, and an MgH_2 + 20wt%NbH composite only released 0.1wt%, 0.28wt%, and 0.57wt% H2, respectively, under the same conditions. Analyses by X-ray diffraction and scanning electron microscopy showed that the composite particle size was small. Energy-dispersive X-ray spectroscopic mapping demonstrated that La and Nb were distributed homogeneously in the matrix. Differential thermal analysis revealed that the dehydriding peak temperature of the MgH_2 + 10wt%LaH_3 + 10wt%NbH composite was 595.03 K, which was 94.26 K lower than that of pure MgH_2. The introduction of LaH_3 and NbH was beneficial to the hydrogen storage performance of MgH_2.

A MICROMECHANICS CONSTITUTIVE MODEL FOR PURE DILATANT MARTENSITIC TRANSFORMATION OF ZrO2 CONTAINING CERAMICS

A new micromechanics constitutive model for pure dilatant transformation plasticity of structure ceramics is proposed in this paper.Based on the thermodynamics,micromechanics and microscale t→ m trans- formation mechanism analysis of the TZP and PSZ ZrO2-containing ceramics,an analytic expressions of the Helmholtz and complementary free energy of the constitutive element for the case of pure dilatant transforma- tion is derived for the first time in a self-consistent manner.By the analysis of energy dissipation in the for- ward and reverse transformations,the mieromechanics constitutive law is derived in the framework of Hill-Rice’s internal variable constitutive theory.

Prospect of new pumped-storage power station

In this paper, a new type of pumped-storage power station with faster response speed, wider regulation range, and better stability is proposed. The operational flexible of the traditional pumped-storage power station can be improved with variable-speed pumped-storage tech no logy. Combined with chemical en ergy storage, the failure to achieve sec on d-order response speed and the insufficient safety and reliability of pumped-storage power units could be solved. With the better solar en ergy and site resources, the in teg rated performance can be improved by an optical storage system in stalled in future pumped-storage stations. Through the characteristics analysis of the new type of pumped-storage power station, three types of optimal station locations are proposed, namely, the load concentration area, new energy concentration area, and ultrahigh- voltage direct current receiver area. Taking the new pumped-storage power station as an example, the advantages of multi-energy cooperation and joint operation are analyzed. It can be predicted that the frequency and load regulation of the power grid will be more flexible, and the service capacity to the main power grid will be much stronger in the future.

Small and Mid-Size Pump-Turbines with Variable Speed

The stability of the grid is jeopardized with the large percentage of non-dispatchable renewables like wind power and also with increasing solar power. This creates various problems because these forms of energy are very volatile and difficult to predict. In most countries the in-feed of these sources must not be curtailed. In addition most of the renewables do not provide short circuit capacity and inertia in the same way as classical units and so further worsen the stability of the grid. The growing exploitation of wind and solar might be limited due to grid stability problems. In order to compensate those problems a large amount of reserve capacity is needed and therefore new technologies for electricity storage are required. Hydraulic pumped storage—the classical storage technology—has some disadvantages. These plants are in mountain regions often far away from wind farms. The distance to the wind farms mean additional loading for the already stressed grid and additional transmission losses. To compensate the very volatile wind energy, the pump input power should be varied continuously. This is so far only possible with variable speed units. Up to now double-fed asynchronous motor-generators are used which are rather expensive. In order to provide a solution for the described situation, ANDRITZ HYDRO has developed a new innovative concept of decentralized pump storage plants. Small standardized pump turbines are combined with a synchronous motor-generator and a full size converter which allows speed variation in pump and turbine mode over a wide range. These plants can be built locally close to wind farms and other sources to be balanced, allowing the increase of renewable energy without increasing the transmission line capacity. For the future smart grids this will be a key storage technology. This concept is reliable, innovative and more economic than other storage technologies.

Stability Enhancement of Small-Scale Power Grid with Renewable Power Sources by Variable Speed Diesel Power Plant

This paper proposes a power control method to improve a stability of a small-scale power grid with renewable energy sources. In an isolated small- scale power grid such as an island, diesel power plant is main power source which has an environmental burden and expensive running cost due to high priced fossil fuel. Thus, expanding installation of the renewable energy sources such as a wind power is strongly desirable. Such fluctuating energy sources, however, harm power quality of the small-scale power grid, and in addition, conventional power plant in the small-scale power grid cannot, in general, stabilize the grid system with such fluctuating power sources. In this study, Variable Speed Doubly-Fed Induction Generator (VS-DFIG) is proposed to be in-stalled at a diesel power plant instead of a conventional Fixed Speed Synchronous Generator (FS-SG), because quick control of a power balance in the small-scale power grid can be achieved by using the inertial energy of VS-DFIG. In addition, utilization of a Battery Energy Storage System (BESS) is also considered to assist cooperatively the VS-DFIG control. As a result of the simulation analysis by using the proposed method, it is verified that frequency fluctuations due to renewable energy source can be effectively reduced by quick power control of the VS-DFIG compared to the conventional FS-SG, and further control ability can be obtained by utilizing BESS. Moreover, the transient stability of a small-scale power grid during a grid fault can also be enhanced.

On Lorentz Transformations and the Theory of Relativity

In the course of a research study on Lorentz transformations and the theory of relativity, the fundamentals of the relativistic concepts of space and time, the relations of those concepts to Lorentz transformations, and equivalence of mass and energy were studied. Many important references on the said subjects were reviewed. This paper draws attention to some critical questions that have risen in the course of that research study on the concepts of expansion of time and unbounded increase of a particle’s mass with velocity.