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Abstract Recently, ZnO‐based composites have been widely applied in the field of electric power. To meet the diverse application requirements, it is necessary to figure out the I–V characteristics of ZnO composites whose high‐voltage and ground‐voltage electrodes are arranged on the opposite sides with a certain horizontal distance. 30 vol%, 40 vol% and 50 vol% ZnO‐based silicone rubber composites were prepared. The horizontal distance between their electrodes was set as 50, 100, 500 μm, 1 and 2 mm, respectively. Results showed that with the increase of ZnO fillers volume fraction under a fixed horizontal distance of 100 μm, from 30 vol% to 50 vol%, the I–V curves shifted left, the leakage current increased and the switching voltage decreased. When the horizontal distance between electrodes increased from 50 μm to 1 mm under a fixed doping concentration of 40%, the I–V curves shifted to the right, the leakage current dropped and the switching voltage rose. The mathematical and physical models were established to explain the results. This work provides a referential significance for the practical application of ZnO composites, such as 5G folding mobile phones and power electronic modules.

Abstract The micro‐defects in epoxy‐based insulation materials generate a local high electric field which results in continuous degradation, seriously endangering the insulation system of gas‐insulated switchgears. A highly sensitive detection technique is reported for micro‐defects of insulation pull rods based on the photon counting (PC) technique. The results demonstrated that for an epoxy‐based insulation pull rod, the photons released during electroluminescence and ionisation at 2 kV, which is less than the partial discharge inception voltage, can be clearly detected. The findings presented a strong correlation between photon counts and defect severity. Discourse has been conducted to elucidate the mechanism behind defect‐induced PC, employing the amplification of ionising luminescence through electric field distortion induced by micro defects and the augmentation of electroluminescence through the aggregation of trap charge. In this regard, the authors verified that PC can serve as a potential tool in the detection of micro‐insulation defects, which also has huge potential in online insulation condition monitoring.

Abstract Discerning weak electric fields has important implications for cosmology, quantum technology, and identifying power system failures. Photonic integration of electric field sensors is highly desired for practical considerations and offers opportunities to improve performance by enhancing microwave and lightwave interactions. Here, we demonstrate a high-Q microcavity electric field sensor (MEFS) by leveraging the silicon chip-based thin film lithium niobate photonic integrated circuits. Using the Pound-Drever-Hall detection scheme, our MEFS achieves a detection sensitivity of 5.2 μV/(m $$\sqrt{{{{{{{{\rm{Hz}}}}}}}}}$$ Hz ), which surpasses previous lithium niobate electro-optical electric field sensors by nearly two orders of magnitude, and is comparable to atom-based quantum sensing approaches. Furthermore, our MEFS has a bandwidth that can be up to three orders of magnitude broader than quantum sensing approaches and measures fast electric field amplitude and phase variations in real-time. The ultra-sensitive MEFSs represent a significant step towards building electric field sensing networks and broaden the application spectrum of integrated microcavities.

Polypropylene (PP)-based recyclable materials have attracted tremendous interest for HVDC cable insulation applications due to their superior electrical properties, e.g., high thermal stability and superior recyclability. Compared with crosslinked polyethylene (XLPE), PP-based materials exhibit the advantages of not only higher working temperatures but also facile and efficient cable manufacturing with reduced costs, which are highly desirable in HVDC cable manufacturing. Considering their promising advantages, PP-based materials have received significant attention from both academia and industry in the field of HVDC cable insulation. In order to adopt PP as a cable insulation material, the mechanical flexibility of PP should be improved. However, regulations of the mechanical properties inevitably influences the electrical properties of PP. So extensive research has been conducted on the regulation of the mechanical and electrical properties of PP. This review summarizes the research progress on recyclable PP-based materials for HVDC cable insulation applications. Particular attention is placed on the electrical property regulations and material structure-property relationships. The challenges that remain to be addressed and the opportunities for future studies on PP-based recyclable HVDC cable insulation materials are also presented.

The ubiquitous power Internet of Things (UPIoT) uses modern information technology and advanced communication technologies to realize interconnection and human-computer interaction in all aspects of the power system. UPIoT has the characteristics of comprehensive state perception and efficient information processing, and has broad application prospects for transformation of the energy industry. The fundamental facility of the UPIoT is the sensor-based information network. By using advanced sensors, Wireless Sensor Networks (WSNs), and advanced data processing technologies, Internet of Things can be realized in the power system. In this paper, a framework of WSNs based on advanced sensors towards UPIoT is proposed. In addition, the most advanced sensors for UPIoT purposes are reviewed, along with an explanation of how the sensor data obtained in UPIoT is utilized in various scenarios.

Polypropylene (PP) is considered to be a rather promising material for HVDC cable insulation. Grafting modi-fication has proved to be an effective method on the electrical property improvements of PP. This paper reports on the highly-enhanced electrical properties of styrene-grafted polypropylene (PP-g-St) and their related mechanism. The influence of grafting styrene on crystallization structures, thermal properties and electrical properties of PP-g-St are characterized and analyzed. These results show that PP-g-St exhibits remarkably enhanced DC volume resistivity, suppressed space charge accumulation and improved DC breakdown strengths as compared to PP. Crystallization observation shows PP-g-St has small, imperfect spherulites with indistinct boundaries, which is strongly correlated to enhanced electrical properties. This study provides an effective grafting strategy to design high-performance HVDC cable insulation materials for bulk power transmission systems.

Abstract With the increase in applied voltage and the decrease in volume, integrated electronic modules have become electrostatic sensitive. ZnO microvaristors doped silicone rubber (SiR) composite, with electric field‐dependent conductivity, shows promising prospects for solving the electrostatic problem. In this study, 20 vol% to 50 vol% ZnO/SiR composite films, filled with 10–30 μm ZnO microvaristors, were prepared and put into the test of electrostatic discharge. Compared with the insulating and conducting materials, ZnO/SiR composites achieve the lowest initial voltage and a short time constant of electrostatic discharge. With the increase of ZnO microvaristors volume fraction, from 20% to 50%, the initial voltage and the time constant of electrostatic discharge drop from 1.78 to 0.72 kV and 3.1 ms to 0.4 μs. When the ZnO volume fraction is higher than 30%, there is no residual voltage after 0.1 s. To explore the reason behind different electrostatic discharge performances of the ZnO/SiR composites, the conductivities of the composites were measured. It is found that the break‐over voltage of the composite drops with the increase in the ZnO microvaristors volume fraction. When a high voltage impulse is applied on the ZnO/SiR film, the composite will turn to the conducting state and release the electrostatic charge adaptively so that the initial voltage can be controlled. This work supplies a novel electrostatic discharge idea for electric and electronic devices.

The requirements for the construction of a new power system inevitably pose significant challenges and changes to the operation and maintenance of the power grid. To ensure the safe and stable operation of ultra-high voltage (UHV) transmission equipment, this work reports on the principles and preliminary results of using electroluminescence (EL)-based photon counting (PC) methods for early detection of micro-defects in GIS/GIL insulation spacer. In this study, the impact of voltage, gas pressure, and gas composition on the photon response of insulation is examined. Furthermore, the corresponding relationship between defect status and photon response characteristics is explored, along with the discussion of the EL mechanism and its evolution induced by defects. The research results demonstrate that PC measurement exhibits high sensitivity to variations in millimeter-scale defect size, position, and morphology at lower electric fields before partial discharge (PD) initiation. With this regard, this paper reveals promising prospects for the early detection of micro-defects in UHV transmission equipment using PC measurement-based methods.

Abstract Recently, demands for high‐performance polymer film capacitors at elevated temperatures have become more urgent. High dielectric constant is essential for dielectric materials to achieve substantial energy density at relatively low electric fields, which is of great significance to practical applications, while improving the permittivity of high‐temperature polymer dielectrics without a remarkable deterioration in other electrical properties still remains a challenge. Here, a polymer nanocomposite containing z‐aligned high‐k nanowires sandwiched by e‐beam evaporation deposited Al2O3 films was developed based on the optimal structure proposed by the phase‐field simulation. It is found that z‐aligned nanowires are more effective in promoting the dielectric constant than random‐aligned ones, and a large increase in dielectric constant is observed at relatively low content of nanofillers. Outer insulating layers effectively suppress the electric conduction and improve the breakdown strength. Consequently, the nanocomposite with only 1 volume fraction of z‐aligned nanowires exhibits a breakdown strength, electrical resistance, and charge–discharge efficiency as high as neat PEI, but more than twice the discharged energy density than it at 150 °C. This study realises the optimal structure predicted by simulation in experiment, obtaining high‐permittivity, high‐temperature nanocomposites at no expense of other electrical properties, and making it possible to achieve high discharged energy density at relatively low electric fields.

Abstract The concept of self‐healing dielectric polymers has been heatedly discussed, with the expectation of high damage resistance and longer service time. However, there is still a lack of analysis on the competitive relationship between electrical degradation and self‐healing. The authors discussed this relationship in two stages: the design of self‐healing strategies and the operation of self‐healing polymers. Since the requirements for excellent insulating or mechanical properties are not consistent with the demands for high self‐healing capability, trade‐offs are necessary during the design of self‐healing polymeric systems. In the operation stage of dielectric polymers, some key factors that affect the service lifetime of non‐autonomous self‐healing dielectric polymers are analysed, including the efficiency and repeatability of self‐healing, and the frequency of healing maintenance. For autonomous self‐healing dielectrics, the simultaneous processes of ageing and healing are investigated using a self‐healing epoxy resin based on microcapsules and in situ‐generated radicals. A quicker recovery of insulating properties, in terms of partial discharge magnitude, was observed under appropriate healing voltages. However, the self‐healing ability might vanish when the voltage was too high, verifying the competitive relationship between electrical degradation and self‐healing.

With the development of smart grids and the energy internet, large-scale monitoring of voltage and electric field data is required in all aspects of power systems, which requires the arrangement of various advanced sensors. Measurement of the electric field can replace traditional voltage transformers to realize the non-contact measurement of voltage, which reduces the insulation cost and the difficulty of operation and maintenance. Electric field measurement can also be applied in various other areas, such as equipment fault diagnosis, lightning warning, and electromagnetic environment measurement. Traditional electric field measurement devices, such as field mills, are bulky and costly, so they cannot be arranged flexibly on a large scale. In this paper, we present an electrostatically actuated micro-electric field sensor (E-sensor) with a piezoresistive sensing structure. The presented E-sensor is fabricated into a four-cantilever structure using microfabrication technology. The cantilevers are displaced under the drive of the electrostatic force, and the generated strain is transformed into measurable signals through piezoresistive materials. The presented E-sensor has the advantages of small size, low cost, low power consumption, and easy mass production. Moreover, the E-sensor has a high signal-to-noise ratio, high resolution, and wide measuring range. The experimental results show that the E-sensor has a linear electric field measurement range from 1.1 to 1100.0 kV·m−1 with an alternating current (AC) resolution of up to 112 V·m−1·Hz−1/2 and a cut-off frequency of 496 Hz, making it suitable for most applications in smart grids and the energy internet.

Abstract Many mainstream dielectric energy storage technologies in the emergent applications, such as renewable energy, electrified transportations and advanced propulsion systems, are usually required to operate under harsh-temperature conditions. However, excellent capacitive performance and thermal stability tend to be mutually exclusive in the current polymer dielectric materials and applications. Here, we report a strategy to tailor structural units for the design of high-temperature polymer dielectrics. A library of polyimide-derived polymers from diverse combinations of structural units are predicted, and 12 representative polymers are synthesized for direct experimental investigation. This study provides important insights into decisive structural factors necessary to achieve robust and stable dielectrics with high energy storage capabilities at elevated temperature. We also find that the high-temperature insulation performance would experience diminishing marginal utility as the bandgap increases beyond a critical point, which is strongly correlated to the dihedral angle between neighboring planes of conjugation in these polymers. By experimentally testing the optimized and predicted structures, an increased energy storage at temperatures up to 250 °C is observed. We discuss the possibility for this strategy to be generally applied to other polymer dielectrics to achieve further performance enhancement.

Abstract Attaining compact energy storage under extreme temperature conditions is of paramount importance in the development of advanced dielectric materials. The polymer composite approach has proved effective towards this goal, and addressing the correlation between filler distribution and electrical properties is foremost in designing composite dielectrics, especially in multifiller systems. Here, the design of a bi‐gradient polymer composite dielectric using an integrated framework based on the phase field model is reported. This framework can predict the charge‐inhibiting behavior of composite dielectrics, which is a key factor impacting the high‐temperature capacitive performance but unfortunately is ignored in conventional phase field models. It is found that due to the traps provided by the functional organic fillers, more carriers are trapped near the electrodes and weaken the electric field, thus significantly suppressing the breakdown initialization process. An interpenetrating gradient structure is designed rationally and synthesized experimentally, which exhibits concurrent high energy density (5.51 J cm−3) and high charge‐discharge efficiency (90%) up to 200 °C. This work provides a strategy to predict the high‐temperature energy storage performance of polymer composites containing charge‐inhibiting components and helps broaden the scope of data‐driven materials design based on phase‐field modeling.

The construction of the future energy structure of China under the 2050 carbon-neutral vision requires compact direct current (DC) gas-insulation equipment as important nodes and solutions to support electric power transmission and distribution of long-distance and large-capacity. This paper reviews China's 10-year progress in DC gas-insulated equipment. Important progresses in basic research and industry perspective are presented, with related scientific issues and technical bottlenecks being discussed. The progress in DC gas-insulated equipment worldwide (Europe, Japan, America) is also reported briefly.

Highlights A strategy that combines multi-mode scanning probe microscopy-based electrical characterization and nano-infrared spectroscopy is developed. A series of samples with different coupling agents and nanoparticles are characterized to unveil the local structure-property correlation of the interface in ferroelectric polymer nanocomposites. The formation of hydrogen bond between the surface modifiers and the ferroelectric polymer enhances the β-phase content and reduces the domain size of the interface, and hence promotes the local piezoelectric effect and breakdown strength.

Abstract The 2050 carbon‐neutral vision spawns a novel energy structure revolution, and the construction of the future energy structure is based on equipment innovation. Insulating material, as the core of electrical power equipment and electrified transportation asset, faces unprecedented challenges and opportunities. The goal of carbon neutral and the urgent need for innovation in electric power equipment and electrification assets are first discussed. The engineering challenges constrained by the insulation system in future electric power equipment/devices and electrified transportation assets are investigated. Insulating materials, including intelligent insulating material, high thermal conductivity insulating material, high energy storage density insulating material, extreme environment resistant insulating material, and environmental‐friendly insulating material, are categorised with their scientific issues, opportunities and challenges under the goal of carbon neutrality being discussed. In the context of carbon neutrality, not only improves the understanding of the insulation problems from a macro level, that is, electrical power equipment and electrified transportation asset, but also offers opportunities, remaining issues and challenges from the insulating material level. It is hoped that this paper envisions the challenges regarding design and reliability of insulations in electrical equipment and electric vehicles in the context of policies towards carbon neutrality rules. The authors also hope that this paper can be helpful in future development and research of novel insulating materials, which promote the realisation of the carbon‐neutral vision.

Abstract To suppress the charge accumulation on the spacer surface in direct current (DC) gas insulated transmission line (GIL) is an important and emergent issue for the development of a clean, safe and economic smart grid. A design method of the DC spacer is proposed, and a spacer prototype is prepared and evaluated both by simulation and type test. The DC withstand voltage test and polarity reversal test are performed using the new DC spacer compared with a commercialised 220 kV AC spacer. The simulation results indicate that the surface electric field and surface charge of the DC spacer are lower than those of the alternating current (AC) spacer under DC voltage. The test results verify that the surface flashover voltage of this DC spacer is higher than that of the AC spacer. The potential feasibility of the spacer design for HVDC is discussed. It is hoped that the content of this paper can bring new ideas in the development of HVDC gas insulated equipment.

Smart dielectric materials with bioinspired and autonomous functions are expected to be designed and fabricated for next-generation electrical insulation. Similar to organisms, such dielectrics with self-adaptive, self-reporting, and self-healing capabilities can be employed to avoid, diagnose, and repair electrical damage to prevent catastrophic failure and even a blackout. Compared with traditional dielectrics, the utilization of smart materials not only increases the stability and durability of power apparatus but also reduces the costs of production and manufacturing. In this review, researches on self-adaptive, self-reporting, and self-healing dielectrics in the field of electrical insulation, and illuminating studies on smart polymers with autonomous functions in other fields are both introduced. The principles, methods, mechanisms, applications, and challenges of these materials are also briefly presented.

Abstract This work reports the effect of octavinyl polyhedral oligomeric silsesquioxane (OvPOSS) on tuning the electrical performance of polypropylene (PP). OvPOSS with different content are introduced into PP using the solution method. The microstructural morphology, crystallinity behaviour, breakdown strength, DC conductivity, space charge formation, and trapping level distribution are measured. The results indicate that the OvPOSS nanofiller can be dispersed uniformly with a doping content of 2.0 phr or less. The DC conductivity is decreased, and the breakdown strength of OvPOSS/PP nanocomposites is significantly increased. The space charge accumulation of the OvPOSS/PP nanocomposites is significantly suppressed due to the introduction of deeper traps by the OvPOSS nanofiller. Finally, the experimental results demonstrate that the OvPOSS nanofiller can greatly increase the electrical performance of the base PP and the OvPOSS/PP nanocomposites have much potential for HVDC applications. They further demonstrate that the PP is environmental‐friendly due to its thermo‐plastic property, which can be recycled after the manufacture.

Abstract ZnO microvaristors/epoxy resin composite has drawn great attention from academia and industry for its adjustable non‐linear conductivity, high mechanical strength, and good ageing resistance. However, the sedimentation of ZnO microvaristors in epoxy resin during preparation is the key problem, which limits its application in engineering. In this study, a novel method of wet winding with polyester fibre cloth is proposed to prepare the ZnO microvaristors/epoxy resin composite. The anti‐settling effect of ZnO microvaristors in the composite is verified by scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA). The microstructure shows that ZnO microvaristors distribute uniformly in the composite, and the content difference of ZnO microvaristors at the top and bottom part is only 0.4%. The composite shows typical non‐linear conductivity, and the threshold electric field and the non‐linear coefficient decrease with the content of ZnO microvaristors, while the conductivity in the insulating state shows an increasing trend. To verify the field grading effect of the composite with non‐linear conductivity (CNC), a finite element model of a needle‐plate electrode, simulating the condition of a conductive tip in a solid insulated system, is set up. CNC can adaptively grade the electric field, which reduces the surface electric field of the needle tip by 86.6% and the highest electric field in the system by 82.1%. This wet winding method solidifies the industrial application of CNC in high‐voltage power equipment.

Polypropylene (PP) exhibits excellent insulation properties, high thermo-stability, and recyclable nature, thus expected to be the next-generation insulation material for HV cable application. Chemical grafting modification is an effective technology to improve the electrical properties of polypropylene. In this paper, we develop and report a new-type grafted PP insulation material by water-phase grafting technology. The comprehensive properties including electrical, thermal, and mechanical of it are tested and compared with traditional cable insulation material—crosslinked polyethylene (XLPE). The results show that the grafted PP holds superior thermal properties and enough mechanical flexibility. The electrical properties are of significant advantages, including resistivity enhanced by nearly two degrees of magnitudes, AC/DC breakdown strength raised by over 20%, and obviously suppressed space charge accumulation. These results indicate that grafted PP is very suitable for application in HV cable systems, either AC or DC. This research lays a foundation for the research and development of the next-generation recyclable polypropylene cables at higher voltage levels.

Abstract Electrical bushings, as important power system components, are critical to the reliability of power systems. The capacitance‐graded bushing is a type of high voltage bushing that is most commonly used in current power systems. However, the limitations of and problems with capacitance‐graded bushings are exposed when the operating voltage level increases. A new direct current wall bushing with adaptive field grading materials is proposed, based on the core features of the problem that the bushing is intended to solve. The main insulation structure of the proposed DC wall bushing with adaptive field grading materials comprises three parts: a field grading layer, a current limiting layer and an electrode extension layer. The proposed bushing has characteristics that include a simple structure, small size and environmental friendliness, and it also meets the requirements of existing power systems. The proposed bushing also conforms to the intended development direction for future power equipment and will aid in the development of power systems for operation at higher voltages.

Dielectric polymers are widely used in electrostatic energy storage but suffer from low energy density and efficiency at elevated temperatures. Here, the authors show that all-organic composites containing high-electron-affinity molecular semiconductors exhibit excellent capacitive performance at 200 °C.

Abstract Polymers are widely used as dielectric components and electrical insulations in modern electronic devices and power systems in the industrial sector, transportation, and large appliances, among others, where electrical damage of the materials is one of the major factors threatening the reliability and service lifetime. Self‐healing dielectric polymers, an emerging category of materials capable of recovering dielectric and insulating properties after electrical damage, are of promise to address this issue. This paper aims at summarizing the recent progress in the design and synthesis of self‐healing dielectric polymers. The current understanding to the process of electrical degradation and damage in dielectric polymers is first introduced and the critical requirements in the self‐healing of electrical damage are proposed. Then the feasibility of using self‐healing strategies designed for repairing mechanical damage in the healing of electrical damage is evaluated, based on which the challenges and bottleneck issues are pointed out. The emerging self‐healing methods specifically designed for healing electrical damage are highlighted and some useful mechanisms for developing novel self‐healing dielectric polymers are proposed. It is concluded by providing a brief outlook and some potential directions in the future development toward practical applications in electronics and the electric power industry.

Generally, the electrical properties of nanocomposite are affected by the type, size, filling concentration and surface treatment process of the nanoparticle. In this study, nanocomposites of polyethylene (PE) with varying filling contents of nano-alumina particles were prepared by the melting blending method and three different kinds of coupling agents were applied for surface modification properties of the nanoparticles. Two of them were silane based and the other was titanate based. The effect of different coupling agents on the dielectric properties was studied. Fourier-transform infrared spectroscopy and thermo-gravimetric analysis were used to verify their compositions. Scanning electron microscope and polarised optical microscopy were used for morphology study. Dielectric permittivity, direct current (DC) volume resistivity and DC breakdown strength characterised their improved insulation performance with nano-alumina as filler. Thermal stimulated current results revealed that adding nano-alumina particles into low-density PE could provide more deep traps and increase DC resistivity.

Surface charge accumulation on the spacers is one of the key issues restraining the development of HVDC GIS/GIL. The precise measurement of surface charge properties provides the basis for further study of the surface charge transport mechanism as well as the charge-induced flashover mechanism under DC voltage. In this study, the authors discuss their perspective on the current status, development needs and potential developing orientation of surface charge characterisation techniques. Different surface potential measurement methods and charge inversion algorithms are reviewed regarding the previous studies and future research needs. Drawbacks and outlooks of surface charge measurement techniques are also discussed with the background of laboratory experiment results and on-site measurements. It is hopefully that this study can serve as a useful guide reference for researchers within the same research field. More importantly, it is authors’ hope that this study can inspire some novel ideas for readers into developing of more accurate and scientific interface charge characterisation techniques.

Many research works have proved that it is viable to predict the radio interference (RI) of high-voltage alternating current transmission lines by corona cage test. However, it is uncertain whether the same method can be adopted for RI prediction of high-voltage direct current (HVDC) transmission lines, since the corona performance of HVDC lines is obviously affected by the widely distributed space charge. In this study, the detailed corona current characteristics, such as the current pulse amplitude, rise time, half-wave time, and repetition frequency are systematically studied by the reduced-scale experiment and the relationship between the average corona current and the RI excitation current is confirmed. Furthermore, based on the experimental study, a method for predicting the RI level of HVDC transmission lines by the corona cage test is proposed. The RI level of a ±800 kV bipolar HVDC transmission line is predicted and compared with the measured result, which verifies the validity of the proposed method.

With the development of modern power systems, especially that of the global energy internet, high-voltage, direct current (HVDC) cable power transmission will play an important role in the future. The key problem of HVDC cable power transmission is the need for novel cable insulation materials that have high performance, recyclability, and higher working temperature to replace traditional crosslinked polyethylene. This paper investigates the thermal and electrical properties of polypropylene (PP)/Al2O3 nanocomposites as a potential recyclable HVDC cable insulation material. The developed nanocomposites exhibit excellent thermal and electrical properties with the introduction of Al2O3 nanoparticles. Particularly, the space charge accumulation is greatly suppressed. Keywords: Global Energy Internet, Power transmission, HVDC cables, Eco-friendly insulation material

In this paper, we present the learning-based data analytics moving towards transparent power grids and provide some possible extensions including machine learning, big data analytics, and knowledge transferring. The closed loops of data and knowledge are illustrated and the challenges for establishing the closed loops are discussed. General ideas and recent developments in supervised learning, unsupervised learning, and reinforcement learning are presented together with extensions for power system applications. Furthermore, much emphasis is placed on privacy-preserving data analysis, transfer of knowledge, machine learning for causal inference, scalability and flexibility of data analytics, and efficiency and reliability of computation. Existing integrated solutions in the industry featuring the Industrial Internet and the digital grid are also introduced.

The development of high-energy-density electrostatic capacitors is critical to addressing the growing electricity need. Currently, the widely studied dielectric materials are polymer nanocomposites incorporated with high-dielectric-constant nanoparticles. However, the introduction of high-dielectric-constant nanoparticles can cause local electric field distortion and high leakage current, which limits the improvement in energy density. In this work, on the basis of conventional polymer nanocomposites containing high-dielectric-constant nanoparticles, oriented boron nitride nanosheets (BNNSs) are introduced as an extra filler phase. By changing the volume ratios of barium titanate (BT) and BNNSs, the dielectric property of polymer nanocomposites is adjusted, and thus the capacitive energy storage performance is optimized. Experimental results prove that the oriented BNNSs can suppress the propagation of charge carriers and decrease the conduction loss. Using poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as the polymer matrix, the P(VDF-HFP)/BNNS/BT nanocomposite has a higher discharged energy density compared with the conventional nanocomposite with the freely dispersed BT nanoparticles.

Abstract This report intends to reveal the role of electron migration and its effects in triggering direct current (DC) surface flashover under temperature gradient conditions when using epoxy-based insulating composites. The surface potential and the surface flashover voltage are both measured using insulators that are bridged between two thermo-regulated electrodes. The space charge injection and migration properties under different temperature are detected. The results show that the surface potential rises significantly because of electron migration near the high voltage (HV) electrode under high temperature conditions, thus creating an “analogous ineffective region”. The expansion of this “analogous ineffective region” results in most of the voltage drop occurring near the ground electrode, which serves as an important factor triggering positive streamers across the insulation surface. This work is helpful in understanding of DC surface flashover mechanism from a new perspective and also has important significance in design of a suitable DC insulator to avoid surface flashover problem.

Polypropylene (PP)-based nanocomposite is a promising insulation material for recyclable high-voltage direct current (HVDC) cables, where the coupling agent plays an important role. In this study, four silane coupling agents with different alkyl chain groups (methyl, propyl, octyl, and octadecyl) were used to surface-modify magnesium oxide (MgO) nanoparticles. The surface-modification effect on the electrical properties of PP/MgO nanocomposites was investigated. The results show that surface-modified nanoparticles introduce quantities of deep traps, whose quantity increases as the alkyl chain length increases. The similar tendency also occurs on DC volume resistivity. All these nanocomposites show remarkable space charge suppression ability and improved DC breakdown strength. Among them, the nanocomposites with octyl-modified MgO show the best electrical properties, which could be attributed to the introduction of a large quantity of deep traps. The work may give a reference for the selection of coupling agents in PP-based nanocomposite insulation material for HVDC cable.

Voltage control of magnetic anisotropy (VCMA) provides an energy-efficient approach to manipulate spintronic devices. Currently, VCMA only shows a weak effect in magnetic tunnel junctions (MTJs) composed of CoFeB/MgO/CoFeB that are the core structure of spintronic memories and logic devices. Multiple approaches have been proposed and studied by researchers to increase the VCMA effect. Here, we demonstrate a large VCMA effect in the CoFeB/MgO/SiO2 double-oxide structure, which can be potentially modified to be compatible with the MTJ cell. The VCMA coefficient as high as 174 fJ/Vm is achieved in this structure at room temperature, with its magnitude comparable to the reported ion-driven VCMA with a high ion-conductive oxide at an elevated temperature. Theoretical analysis indicates that the large VCMA is a magnetoionic effect, which is dominated by ion migration and can be explained by a nanograin cluster model. This double-oxide structure is promising to be extended to an MTJ structure to reduce switching energy in spintronic devices.

In this study, an inter-turn fault diagnosis method is proposed based on deep learning algorithm. 12-channel data is obtained in MATLAB/Simulink as the time-domain monitoring signals and labelled with 16 different fault tags, including both primary and secondary voltage and current waveforms. An auto-encoder is presented to classify the fault type of the abundant and comprehensive fault waveforms. The overall waveforms compose a two-dimension data matrix and the auto-encoder is trained to extract the features in the multi-channel waveforms. The selected features are convoluted with the original data, generating a one-dimensional vector as the input to the softmax classifier. Variables such as type, activation function and depth of auto-encoder, sparsity of sparse auto-encoder, number of features and pooling strategies are studied, which gives an intuitive process to train a proper learning model. The overall recognition accuracy reaches 99.5%. Signal characteristics such as channel selection, time span of the input signal and signal sampling frequency are studied to find the best solution for the inter-turn fault detection of the three-phase transformer. The proposed method under deep learning framework increases the accuracy and robustness in transformer fault diagnosis, indicating its potential and prospect in the next-generation smart transformers.

Lightning is the main cause of transmission line failure, and it is important to improve the lightning protection level of the transmission line for the stability of the power system. Traditional solutions for the shielding failure of transmission lines is to use the electrical geometric model method. However, with the improvement of the voltage level, the physical size increases, and the calculation of lightning protection for ultrahigh-voltage dc lines has a greater difference with operating experience. Based on the Ningxia-Shandong dc transmission lines in China, this study utilised the lead development model to describe the flashover of insulators and the breakdown of the gaps. A comprehensive calculation method of shielding failure trip-out rate considering terrain, earth resistance and weather was proposed. The accuracy was much higher when compared with the traditional calculation and the result can be a reference for other similar calculation for dc lines.

With the development of high-voltage direct-current (HVDC) transmission projects, the issue of electromagnetic compatibility has become more and more severe, especially the synthetic ion flow electric field. The DC electric field is inseparable from the equipment insulation, the safety of the system operation, and effects on organisms nearby. The measurement of the synthetic electric field of ion flow has been a major difficulty due to the influence of ion currents and distorted field. A differential electric field sensor for measuring the synthetic electric field is proposed. The calibration method and the experimental device for the measurement of the air synthetic electric field of ion flow are presented. Calibration experiments show that the calibration method is practical and effective, and the test result from the sensor is in good agreement with the theoretical value. The experiments in the library show the validity of the calibration method and the excellent performance of the sensor.

Lightning and lightning induced effects have significant influence on many aspects affecting the public, which makes the research of lightning and lightning protection very important. However, due to the strong randomness and complex discharge mechanisms of lightning, the understanding of lightning is still far from satisfactory. On the basis of the International Conference on Lightning Protection 2014, this study gives a review of recent progress on lightning and lightning protection research covering the following aspects: lightning locating and observation, lightning physics, lightning electromagnetic transients, and lightning protection for various systems. The goals of this study are to give readers an overall introduction to the recent progress in lightning and lightning protection research, and to motivate them to conduct further studies to address the unsolved problems in lightning-related research.

A comprehensive review on the methods used for fault detection, classification and location in transmission lines and distribution systems is presented in this study. Though the three topics are highly correlated, the authors try to discuss them separately, so that one may have a more logical and comprehensive understanding of the concepts without getting confused. Great significance is also attached to the feature extraction process, without which the majority of the methods may not be implemented properly. Fault detection techniques are discussed on the basis of feature extraction. After the overall concepts and general ideas are presented, representative works as well as new progress in the techniques are covered and discussed in detail. One may find the content of this study helpful as a detailed literature review or a practical technical guidance.