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The interpretation of the surface charge pattern of spacers in gas-insulated transmission lines (GIL) is a research topic with great importance, which requires a comprehensive understanding of charge behaviors at physical interfaces. Here, we report a surface charging phenomenon of spacers in the presence of metal particles inside the direct current (DC) GIL. The charging of spherical metal particles on the spacer surface appears as dotted discontinuously distributed charge spots, which are due to the charge injection from the induced charge of the metal particle and gas ionization over the metal particle surface. Concentrically distributed bipolar charge patterns are seen to build up, which are due to the surface trapping of charges from gas ionization at the end tip of the acicular metal particle. The lateral type of ionization obeys the law of dielectric barrier discharge of the needle-plate electrode in an intense DC electric field, which may bring significant influence on the safety of the spacer. The study in this letter provides direct evidence demonstrating the surface charge patterns of spacers in the presence of metal particles, which serves as an important basis for the design of DC GIL.

Electrostatic discharge (ESD) is a phenomenon that commonly exists on the insulation surface in electrical and electronic devices at different environmental conditions. In this letter, the surface charge pattern of PMMA subject to ESD at the different relative humidity (RH) is presented by Lichtenberg figures. The influence of RH on discharge processes is discussed. The results show that the voltage amplitude, polarity, and the shape of the electrode during ESD all have a significant influence on the surface discharge process. The surface discharge pattern at positive ESD is plum blossom-like while at negative ESD the surface discharge pattern presents a star-like pattern. The ESD process can be suppressed under the high RH condition. The study of this paper provides direct evidence on how ESD process is mitigated at different RH.

The current monitoring of bundle conductors is essential for precisely locating operation failures in transmission lines, leading to a more stable and reliable power grid. This paper proposed a novel method for current reconstruction of bundle conductors, utilizing tunneling magnetoresistive (TMR) sensors. Both the normal and abnormal situations are discussed. The optimal and sub-optimal measurement points for sensors were obtained for concise current measurement with only one uniaxial TMR sensor. The current in each bundle conductor was calculated separately based on the comprehensive algorithm. Validation experiment indicated the error of the measurement and calculation system was no more than 10%, proving the robustness and feasibility of the measurement system and the algorithm. The reconstruction process takes full advantages of TMR sensors and provides a promising solution for transmission line monitoring in power grid.

High voltage cables now have been widely applied in electric power systems. A prefabricated rubber stress cone is the key part of high voltage cable terminal, and its property is the main factor in determining whether the high voltage cable operates safely. In this paper, the finite element numerical simulation is applied to analyze the distribution of electric field intensity. Instead of using materials with fixed conductivity, materials with nonlinear conductivity are used as the insulation material for rubber stress cones. The polymer composites with nonlinear conductivity that depends on applied electric fields can smartly smooth the nonuniform electric fields in insulation components of power systems through varied material parameters with the electric field. Combined with theoretical analysis, we can determine the parameters range of nonlinear conductivity materials. By comparing the electrical field distribution of different materials, it is found that nonlinear conductivity polymer composites can effectively improve the electric field at the rubber stress cone face and the junction of stress cone terminal, which is of significance in the development of higher voltage cable in the future.

Polymer nanocomposites with high dielectric permittivity (e) are urgently demanded for power energy storage. In this research, in order to prepare nanocomposites with strong interfacial interactions and higher e, a novel surface modification molecule, 3,4,5-trihydroxybenzoic acid (or Gallic acid, GA), was developed. There are two main advantages for selecting GA as the coating molecule. Firstly, the polar groups, such as hydroxyl and carboxyl groups in GA, could form hydrogen-bonding interaction with poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE). Therefore, though thickness of coating layer is only 1.6 nm, nanocomposites with better dispersion were prepared by strengthening hydrogen-bonding interaction at polymer-nanoparticle interface. Secondly, functional groups with high bond dipole moment, such as carboxyl groups and phenolic groups, are beneficial to obtain high e in PVDF-CTFE + BT@GA. e is 25.6 at 1 kHz with 12.9% BT@GA. This is about 2.5 times higher than that of PVDF-CTFE matrix (10.4 at 1 kHz). The hypothesis in this research might offer a feasible approach to prepare capacitors with higher e and higher energy density by regulating bond dipole moment of functional groups in the coating molecules.

Polymeric materials filled with ZnO varistors microspheres can exhibit the intriguing nonlinear current-field characteristic that is promising for electrical field grading applications. However, the switching field of the composite material is hardly controllable by current approaches, and the nonlinear current-field characteristic of the composite material is attained at the expense of significantly compromised mechanical properties. In this study, we developed silicone rubber (SR)-based ternary composites containing ZnO microspherical varistors and carbon fibers (CF) for simultaneous control over the electrical and mechanical properties to satisfy the practical requirement in electrical field grading. The measured J-E characteristics showed that introducing CF into conventional ZnO microspherical varistors/SR binary composites could largely broaden the range of switching field and improve the nonlinear characteristic. The mechanical tensile tests of the ternary composite samples revealed remarkably enhanced mechanical properties compared with ZnO microspherical varistors/SR binary composites. This paper demonstrated the synergistic effect in tailoring the nonlinearity and mechanical performance of nonlinear polymeric composites for advanced field grading materials.

The zinc-oxide (ZnO) varistor is widely used to limit the overvoltage in the power systems, and its quality is closely related to the safety of the entire protected system. In this paper, accelerated aging experiments under different current levels were carried out on the ZnO varistors to study the harmonic characteristics of the leakage currents in the aging process. It is found that the proportions of higher order harmonics in leakage currents increase faster after several impulse tests and then a sudden decrease appears before the varistor fails, which is caused by the decrease of the varistor voltage. And based on this, a new criterion for the aging of the ZnO varistor is put forward.

Due to the effect of the space charges, there is still a lack of effective methods to predict the corona effects of HVDC transmission line based on cage tests. This paper presents a method of using the corona cage to evaluate the radio interference of HVDC transmission lines. First, the condition under which the tests of a corona cage can be equivalent to those of an HVDC transmission line is discussed theoretically. It shows that the key is to make the electric-field distribution around the conductors in the corona cage the same as that around the transmission line. Then, a numerical approach and the Kaptzov's assumption are used to obtain the applied voltage on the conductors in a corona cage in order to set up the same electric-field distribution as that around the transmission line. Reduced-scale tests both in time domain and in frequency domain show that the method is effective. The method can also be extended to investigate the dc corona and its other effects based on cage tests.

Self-powered wireless sensor networks based on autonomous wireless sensor nodes have been increasingly attractive due to the outstanding merits of maintenance-free and self-sustainability. In spite of the explosive growth of the wireless sensor network techniques, the corresponding power supply methods with miniaturized, low-cost, flexible, reliable, and efficient designs are still limited. In this paper, a novel magnetic energy harvester based on nonlinear resonance is presented, which has been verified to be capable of scavenging energy from the power-frequency (50 or 60 Hz) magnetic field distributed around the transmission line. We have theoretically and experimentally demonstrated the greatly enhanced harvesting properties in both power density and enlarged bandwidth, which provides great robustness to frequency fluctuations of magnetic field. A prototype of this brand new design is fabricated and tested. Experimental results show that the prototype is capable of harvesting a power as high as 13.5 mW at merely 2.4 Oe (RMS) power-frequency AC magnetic field. The high power density (0.5625 mW/cm3 at 2.4 Oe) and the wide working bandwidth (2.6 Hz) promise its application prospects as a sufficient and reliable power supply for sensors in the smart grid.

Extruded polymeric HVDC cables have drawn great attention in modern power systems. This paper reviews the history and development of the polymeric HVDC cables and summarizes the key technical problems in extruded HVDC cables. It is pointed out that two key issues should be solved. One is the electric field inversion within HVDC cable insulation which is caused by the temperature and electric field dependent DC volume resistivity of the polymeric insulation materials. The other is the space charge behavior under multi-fields coupling, including charge injection, transportation, accumulation and dissipation characteristics. The following aspects need to be particularly concerned in the future: the interaction between temperature, electric field, space charge and DC volume resistivity under multi-fields coupling; mechanisms of nanoparticles doping on enhancing the properties of polymeric insulation material; the long-term operation characteristics of nanodielectrics; collaborative optimal regulation methods and theories on the properties of polymeric insulation material; and recyclable insulation materials for future HVDC cables.

To study the surface charge distribution of high-voltage direct-current (HVDC) spacers for gas insulated lines (GIL), a surface charge inversion algorithm based on surface potential measurements is necessary. However, previous studies on inversion calculation of surface charge density only considered the surface potential of one side, neglecting the effect of residual surface charge on the other side of the spacer; this leads to an inaccurate inverted surface charge distribution. In this paper, the inversion algorithm methods used to determine surface charges over the past few decades were summarized, and their advantages and disadvantages were discussed. Based on the previous charge inversion algorithms, an improved surface charge inversion algorithm considering the surface potential of both sides of a cone-type model spacer was developed. The improved method was verified experimentally using a cone-type model spacer. Compared with that obtained by previous charge inversion algorithms, the charge distribution derived from the improved algorithm was closer to the situation determined from theoretical analysis. This work has practical relevance for the surface charge measurement of cone-type spacers and offers a new orientation in the surface charge analytical algorithm.

Due to the wide application of high-order resonant and nonlinear electric equipment in the UHVDC converter station, the electromagnetic transient process is a complex issue during the short-circuit fault transient of the system caused by lightning strike or other reasons. In this study, firstly, an operating ±800 kV DC line is artificially short-circuited to simulate the flashover fault process. The instantaneous voltages and currents and the electrical fields are measured by advanced sensors and high sampling rate recording devices at different points in the converter station, in order to comprehensively study the high-frequency characteristics of the UHVDC system. Then, the portal impedances of the major UHVDC equipment as well as the stray parameters are systematically measured in an actual ±800 kV station. Based on the data measured, the accurate high-frequency characteristics of the ±800 kV converter station are analyzed. The results of the study can be used to guide the EMC and relay protection designs of the UHVDC converter station, so that the stability of the system can be improved.

An inversion method for evaluating lightning current waveforms from measured electromagnetic field data based on time series neural network (TSNN) is presented in this paper. The back-propagation neural network (BPNN) is also adopted to evaluate the channel-base current using measured electromagnetic field data, and comparisons of inversion results between TSNN and BPNN are presented. The inversion results are in good agreement with corresponding measured channel-base currents. The proposed method can evaluate the channel-base current in areas with complex terrain, and it is useful for studies on lightning-protection in power systems and lightning characteristics

Polypropylene (PP) has shown great potential as recyclable HVDC cable insulation material. This paper aims to investigate the effect of different nanoparticles on tuning the electrical properties of PP. Surface modified MgO, TiO 2 , ZnO and Al 2 O 3 nanoparticles with various contents were melt blended with PP. The microstructural morphology, dielectric properties, DC volume resistivity, space charge behavior and DC breakdown strength of the nanocomposites were investigated. It was found that the dielectric permittivity all increases with the increase of nanoparticle content, only the dielectric loss of TiO 2 /PP nanocomposites increases. For MgO and TiO 2 nanocomposites, the DC volume resistivity increases with the increase of nanoparticle content and then decreases, while it continues to increase for Al 2 O 3 nanocomposite. TiO 2 /PP nanocomposite with 5 phr nano-TiO 2 shows lower volume resistivity than PP. Space charge suppression and DC electric breakdown strength show similar variation trend, both increase with the increase of nanoparticle content and then decrease. MgO and TiO 2 nanocomposites show the most obvious space charge suppression and TiO 2 nanocomposites exhibit the highest DC breakdown strength, which is 43% higher than that of pure PP. Considering the electrical properties investigated, the optimal content for MgO, TiO 2 , ZnO and Al 2 O 3 nanoparticles is about 3, 1, 1 and 1 phr, respectively. Among these four kinds of nanoparticles, MgO and TiO2 nanoparticles are more capable than ZnO and Al 2 O 3 nanoparticles to modify the electrical properties of PP and more potential to be used as recyclable HVDC cable insulation material.

In this work, we studied multiple doping of ZnO varistors with Ga 2 O 3 and In 2 O 3 and determined its effect on electrical properties, characterized by using scanning electron microscopy, current–voltage testing, capacitance–voltage testing, and X-ray diffraction. At a given gallium concentration, the residual voltage ratio of the sintered varistors decreased clearly with the indium dopant concentration increased. Additionally, with increasing indium dopant concentration, the average grain size decreased slightly, and the voltage gradient was improved. The varistors containing 0.045 mol% indium and 0.4 mol% gallium showed optimal performance, exhibiting a residual voltage ratio of 1.54, as well as a voltage gradient of 462.5 V/mm, a leakage current of 1.30 µA/cm 2 , and nonlinear coefficient of 72.3. Such co-doped ZnO varistors can provide better protection when used in surge protectors.

The ion mobility is the one of the basic parameters in the study on gas discharge. There are many environmental parameters affecting the average mobility of ions in air. Among them pressure and humidity are important factors. Until now there is no uniform average mobility of ions in air in practice. This paper presents the results of a series of experiments on the influence of pressure and humidity on the average mobility of ions in air. Firstly, an improved analysis method to deduce the average air ion mobility in air is presented with the help of an apparatus for generating parallel-plane ion flow field. Then, the mobility is measured in a climatic test cabinet. The positive and negative mobilities in the air with the pressure from 80 to 110 kPa and the relative humidity from 20% to 80% at the room temperature are provided. Finally, the rule of mobility-pressure-humidity variation curve is discussed and the specific formula for average mobility of ions in air with respect to pressure and humidity is then raised.

In the present study, the effect of indium doping on the micro-characteristics and electrical properties of ZnO varistors co-doped with Al2O3 and Y2O3 were determined. Scanning electron microscopy, current-voltage testing in a range from small to large current, capacitance-voltage testing, and X-ray diffraction pattern testing were conducted. The results show that both the residual voltage ratio and the leakage current of sintered ZnO varistors decrease and then increase as the indium dopant increases at a given aluminum and yttrium content. The nonlinear coefficient shows an inverse relationship. In addition, the voltage gradient of the samples increases as the indium dopant increases. The sintered ZnO varistor samples with 0.02 mol% indium, 0.2 mol% aluminum, and 0.9 mol% yttrium show the optimal performance, exhibiting a 1-mA residual voltage of 448 V/mm, a leakage current of 0.69 µA/cm2, a nonlinear coefficient of 76, and a residual voltage ratio of 1.58. This study has great significance for improving the protective effects of surge protection devices assembled with ZnO varistors and the stability of power systems.

The light emission during the growing of the electric tree has been studied before, but very little is known about it before the electric tree initiation. The aim of this work is to study the light emission before electric tree initiation in insulate materials under high AC stress. The ultra-sensitive photomultiplier tube is used to detect the photons in a darkroom and a series of optical filters are used to investigate the spectrum of the photons. The existence of photons before tree initiation is proved and the pattern of them during an AC cycle is observed. The spectrums of the light emission in different dielectric materials are acquired and provide some evidence for the interaction between free charges and polymer molecules. Although the investigation of the light emission is far from being complete, it is found that the light emission under AC voltage starts with the recombination of opposite charges and the interaction process begins under a higher electric field. Based on the experimental results, a brief charge behaviour model is built up.

This study determined the effect of indium doping on the electrical properties of Al-doped ZnO varistors. Scanning electron microscopy, current-voltage testing in a range from small to large current, capacitance-voltage testing, and X-ray diffraction pattern testing were carried out. The results show that both the voltage gradient and nonlinear coefficient of sintered ZnO varistors increase and then decrease with increasing indium dopant at a given aluminum content. Meanwhile, the leakage current and residual voltage ratio show an inverse relationship. The varistor ceramic with 0.015 mol% indium and 0.02 mol% aluminum has optimal performance. This work is helpful for improving the protective effects of ZnO varistors and increasing the safety of electrical systems.

Non-intrusive load monitoring addresses the challenging task of decomposing the aggregate signal of a household's electricity consumption into appliance-level data without installing dedicated meters. By detecting load malfunction and recommending energy reduction programs, cost-effective non-intrusive load monitoring provides intelligent demand-side management for utilities and end users. In this paper, we boost the accuracy of energy disaggregation with a novel neural network structure named scale- and context-aware network, which exploits multi-scale features and contextual information. Specifically, we develop a multi-branch architecture with multiple receptive field sizes and branch-wise gates that connect the branches in the sub-networks. We build a self-attention module to facilitate the integration of global context, and we incorporate an adversarial loss and on-state augmentation to further improve the model's performance. Extensive simulation results tested on open datasets corroborate the merits of the proposed approach, which significantly outperforms state-of-the-art methods., Accepted by IEEE Transactions on Power Systems

Surface charge accumulation on cone-type spacers restricts the development of dc gas-insulated substations (GISs) and gas-insulated transmission lines (GILs). In previous studies, many surface charge tailoring methods were investigated. However, indirect tailoring of surface charge by temperature field regulation has not been performed. In this paper, the relation between the temperature field distribution and the surface charge accumulation is studied by experiment. And a temperature control method by doping K2O·6TiO2 whiskers in the composite of epoxy resin is introduced and verified by experiment. The results show that the doping of K2O·6TiO2 is able to weaken the surface charge accumulation in both air and SF6.

The capacitor bushing is the most commonly used bushing in power systems. However, the use of the capacitor bushing is limited by the complexity of the insulation and grading electric field structure. At the same time, as the voltage grade of the power system increases, the bushing needs to be made larger and its manufacture is more complicated, limiting the use of the capacitor bushing for such power systems. In light of present high-voltage bushing problems, the present paper proposes a new type of high-voltage bushing structure that adopts a three-layer structure with nonlinear composites for internal insulation to replace the original bushing condenser in a capacitor bushing. From the inside to outside, the three layers are a uniform-voltage layer, leakage-current-limiting layer, and electrode extended layer. The uniform-voltage layer and electrode extended layer made from materials having nonlinear conductivity are used to make the electric stress uniform in the main insulation and at the edge of the flange, avoiding breakdown of the main insulation and flashover of the flange. The design of the new bushing is applicable to a variety of voltage levels of DC power systems. At the same time, the new bushing is smaller, the production of the bushing is simpler, and the risk of a bushing fault is reduced, marking a technical innovation for high-voltage bushings in power systems.

High-sensitivity and miniaturized measurement of electric fields is important for applications in power grid such as lightning waveform capturing and electrical equipment monitoring. In addition, the demand of wide-area information measurement in smart grid also necessitates the development of miniaturized and noncontact sensors. So far, there have already been a variety of electric-field sensing devices. However, these approaches meet the challenges of large size and low sensitivity. To solve the problem, this paper proposed a new electric-field sensor based on piezoelectric effect. The piezoelectric effect enables the conversion of electric fields into piezoelectric material deformations and then the air-gap capacitances in the device. The results indicate that the electric-field micro sensor can reach a high sensitivity of 30 V/m. The side length of the sensor chip can be as small as a few millimeters. Owing to the feasibility in mass production of the proposed sensor, it can potentially be extended to the industrial applications in power grid.

It is important for us to study what have changed on electrical property of polymer after electrical tree aging occurs when we explore the self-healing of electrical degradation of polymers. Leakage current characterization has been demonstrated in this paper and is useful to give these advices. Electrical trees of different shapes and different electrode structures are formed and the high field leakage current are measured. The mechanism of leakage current variation of electrical tree samples is explored and confirmed by experiment designed. The polarization index and absorption ratio are also calculated and seem to behave no obvious pattern during the extending of tree channels. In conclusion, the high field leakage current is an effective non-destructive characterization of the electrical tree defects.

Prefabricated rubber accessories affect high-voltage cable operation because they determine the electric field distribution within a cable joint. For a DC power cable, the electric field distribution depends on the electrical conductivity of the insulation material, which is strongly affected by temperature. In this paper, instead of traditional rubber cable joints with a semiconductive rubber material as the stress cone and inner deflector shield, a field grading material with a strongly nonlinear conductivity is used to achieve better grading electric field performance. To study the electric field distribution of a DC cable joint under various temperature conditions, a finite element numerical simulation is conducted using COMSOL Multiphysics. A comparison of the electric field distribution of various models shows that polymer composites with nonlinear conductivity effectively improved the electric field distribution in the cable joint, especially for high temperature gradients. It is shown that a field grading material has great potential for high-voltage DC cable joint design, facilitating the development of higher-voltage DC cables.

In this work, we studied multiple dopants based ZnO varistors and optimizing its microstructure and electrical properties by tailoring the sintering characteristics. The properties were evaluated by scanning electron microscopy (SEM), current-voltage characteristics, capacitance-voltage characteristics, dielectric characteristics and X-ray diffraction characteristics. At a given gallium and indium concentration, the residual voltage ratio of the sintered varistors under the 5/20μs impulse current decreased obviously as the sintering temperature increased from 1100°C to 1250°C. Besides, the nonlinear coefficient was first increased and then decreased with increasing sintering temperature. The multiple doped ZnO varistors sintered at 1250°C showed optimal performance, exhibiting a grain size of 7.1μm, residual voltage ratio of 1.56, voltage gradient of 416 V/mm, leakage current of 0.79 μA/cm2, and nonlinear coefficient of 73. When applied in power systems, the high voltage gradient varistors will make the line surge arrester in better coordination with insulators as well as reach the goal of low cost and miniaturization of GIS tank-type arresters.

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.

DC partial discharge in gas generates many space charges. Because these charges move with the electric field, change the electric field and accumulate on the surface of sensors, it is difficult to measure the electric field in the space. Based on the relationship between the charge accumulated on the surface of the dielectric in the ion flow field and the applied electric field, this paper proposes a simple method to measure the electric field with space charges using a suspended dielectric as a sensor. By testing the charge accumulated on the suspended dielectric, the applied electric field can be determined. The method is verified and the factors that affect the measurement result are investigated by experiments in a predictable and controllable ion flow field. The results show that when saturation of the accumulation of the space charge on the suspended disc is reached, the total accumulated surface charges are linear with the normal component of the external applied electric field. The ion flow density just affects the speed of the charge accumulation and does not affect the amount of saturated surface charges. The relationship coefficient between the surface charge and the electric field can be obtained through calibration. Unlike other methods that regard the accumulation of charge on the sensor as the key interference, the method in this article just uses the accumulation characteristics of the charge on the sensor, which is simple and feasible.

Ferroelectric polymers have been widely explored for film capacitor applications due to their high energy storage densities that are almost an order of magnitude greater than those of the commercial capacitor dielectrics. However, the existing ferroelectric polymers are designed exclusively for room-temperature operation, and suffer from poor capacitive performance at elevated temperature, which falls short of the need in the emerging harsh-environment applications. In this paper, we report multilayered ferroelectric polymer composites exhibiting simultaneous high energy density and high discharge efficiency at elevated temperature. The multilayered composites consist of two copolymers of polyvinylidene fluoride (PVDF) with similar chemical structures but distinct dielectric properties, where one contributes to high electrical polarization and the other offers high thermal stability and suppresses charge injection. More importantly, we demonstrate that the critical issue of charge conduction at elevated temperature in ferroelectric polymers is well tackled by the established highly miscible interlayer interfaces in the multilayered structure set up between the two electrically dissimilar phases. At 70 °C, the maximum discharged energy density above 80% discharge efficiency of the multilayered composites reaches 15.5 J/cm3, far outperforming all the existing ferroelectric polymers. This work sheds light on the design of high-energy-density ferroelectric polymers for high temperature capacitive energy storage.

ZnO varistors with high energy absorption capability and aging stability were fabricated. The main prescriptions of ZnO varistors include 94.09 mol%ZnO, 1.0 mol%Bi 2 O 3 , 0.75 mol%MnO 2 , 1.0 mol%Co 2 O 3 , 0.5 mol%Cr 2 O 3 , 1.0 mo.%Sb 2 O 3 , 1.2 mol%SiO 2 , 0.1 mol%Al 2 O 3 , and 0.36 mol%Ga 2 O 3 . The varistors maintained a large voltage gradient and a high nonlinearity. AC accelerated aging test performed under 0.9 U 1 mA at 115 °C with 1000 h showed that the ZnO varistors were stable. The varistors without being aged were in good condition after being struck 18 times by a 400 A square wave energy pulse. The absorption energy was more than 327 J/cm 3 and the degradation rate coefficient ( K t ) was 0.04. These values are suitable for manufacturing 1000 kV ultra-high voltage surge arresters.

The interfacial region between a nanoparticle and the polymer matrix is considered to have an important effect on the properties of nanocomposites. In this experimental study, the tuning effects of surface-modified TiO2 nanoparticles on the aggregation structure and trapping property of the nanocomposites are investigated. The addition of TiO2 nanoparticles increases the number of spherulites and decreases their sizes. It is also found that TiO2 nanoparticles can suppress the mobility of chain segments in the interfacial region, suppress crystallization, and reduce the crystallinity, depending on the surface modification and loading levels of nanoparticles. On the basis of the conclusions, the model of a spherulite and the interface is established and the trap distribution of the interface is analyzed according to the results of TSC measurements. It is assumed that there is a strong correlation between traps and the charge transport of nanocomposites, and the mechanism of charge transport is discussed wit...

Electromagnetic transient processes are strongly related to the parameters of transmission lines. With the ground return parameters considered, the frequency dependent parameters of transmission lines are highly dependent on the soil parameters, which include resistivity and dielectric permittivity. In this paper, with the measurement results of frequency variation of soil parameters, the influence of the frequency dependent soil parameters on the frequency dependent characteristics of the transmission line parameters were studied using the complex return plane method. According to the calculation results, the frequency characteristics of soil parameters have obvious influences on the parameters of overhead transmission lines. The influences of the humidity, temperature and particle size of the soil on the ground-return parameters were also evaluated.

Induced lightning is the major cause of interruptions in power distribution lines. To reduce lightning accidents and improve the power supply reliability, it is significant to study the characteristics of the induced lightning overvoltage by experiment and calculation. In the paper, a calculation method of lightning induced overvoltage, considering lightning leader progress, non-ideal ground corona effect, field-line coupling, was introduced. The accuracy of the program was verified by comparison between calculated results and the practical experimental results, the calculation results are close to the experimental data. A scaled experiment was carried out to obtain the basic relationship between lightning and overvoltage on distribution lines. Influence factors on overvoltage were analyzed.

Polymer dielectrics with high thermal conductivity and low dielectric loss are highly attractive for applications in electric and electronic industry. In this paper, surface modified aluminum nitride (AlN) nanoparticles were introduced into polypropylene (PP) matrix via melt blending to prepare thermoplastic dielectrics with enhanced thermal conductivity and low dielectric loss. The microstructure, DC conductivity, dielectric properties, breakdown strength, space charge behavior, thermal conductivity and thermal stability of the nanocomposites were investigated. It is found that the inclusion of surface modified AlN nanoparticles results in improved thermal conductivity and thermal stability of PP/AlN nanocomposites. The dielectric constant shows a slight increase with AlN nanofiller content, and the dielectric loss remains at very low level of below 0.003. DC conductivity of PP/AlN nanocomposites increases but shows desirable weak dependence on electric field. DC and AC breakdown strength slightly decrease with the AlN nanoparticle content but it is still high enough for dielectric applications. More importantly, the PP/AlN nanocomposites is a thermoplastic material which is potential to be recycled and has less impact on the environment.

As basic insulating material, epoxy resins are widely used as the matrix of insulators in HVDC transmission system. In most cases, alumina of micro range is blended to improve mechanical properties as well as reduce expenses, etc. However, apart from benefits, the incorporation of micro-particles could alter surface electric behaviors due to the change in material structures and the surface trap distribution under operating condition. Therefore, the surface charge behavior under dc is changed as well, which can affect the surface flashover characteristic. Direct fluorination is a method to change surface properties by introducing stable C-F structure to the surface of the dielectric material. The newly formed fluorinated layer could bring changes to electrical characteristics, thus affecting surface electrical properties under dc stress. In this paper, samples are prepared using alumina casted epoxy resin composites. The two parts are blended using the same process used to produce cone-type insulators in gasinsulated substations (GIS) in industrial application. Experiment samples were treated with F2 /N2 mixture containing 12.5% F2 in volume at 50 °C under 0.1MPa. The scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR) were used to investigate surface physicochemical characteristics. Water and diiodomethane droplet contact angles were measured and surface energies were calculated. The distribution of the surface voltage potential, as well as the surface conductivity and DC flashover voltage were measured. Experiment results confirmed that the fluorination to epoxy resin and alumina composites can change the surface morphology by changing the exposed area of surface alumina particles. It also showed that fluorinated samples have higher DC flashover voltage in both air and SF6 due to the combined effect of the change in the surface morphology and the surface conductivity.

Lightning protection analysis is of vital importance for the transmission system, on which the grounding impedance model has a great effect. This paper concerns the influence of the grounding impedance model on lightning protection analysis. The transmission system is established in PSCAD/EMTP with consideration of three grounding impedance models as constant resistance, standard dynamic resistance and real-time dynamic resistance. The lightning withstand level is simulated and obtained under several typical conditions of soil resistivity and voltage levels. Moreover, the models are comparison and analyzed in the aspects of the dynamic resistance, as well as the ground potential rise and the insulator voltage. This makes a contribution for determining the suitable grounding impedance model applied in the lightning protection analysis, which is very meaningful both in theory and practice.

This work reports the advances of utilizing a core@double-shell nanostructure to enhance the electrical energy storage capability and suppress the dielectric loss of polymer nanocomposites. Two types of core@double-shell barium titanate (BaTiO3) matrix-free nanocomposites were prepared using a surface initiated atom transfer radical polymerization (ATRP) method to graft a poly(2-hydroxylethyle methacrylate)-block-poly(methyl methacrylate) and sodium polyacrylate-block-poly(2-hydroxylethyle methacrylate) block copolymer from BaTiO3 nanoparticles. The inner shell polymer is chosen to have either high dielectric constant or high electrical conductivity to provide large polarization, while the encapsulating outer shell polymer is chosen to be more insulating as to maintain a large resistivity and low loss. Finite element modeling was conducted to investigate the dielectric properties of the fabricated nanocomposites and the relaxation behavior of the grafted polymer. It demonstrates that confinement of the more conductive (lossy) phase in this multishell nanostructure is the key to achieving a high dielectric constant and maintaining a low loss. This promising multishell strategy could be generalized to a variety of polymers to develop novel nanocomposites.

With the application of ultra-high-voltage (UHV) technology, how to reduce the construction cost of the UHV substations is becoming an important and emergent issue. In this paper, two kinds of one-column-varistor arresters are used to replace conventional four-column-varistor arresters for busbars or transformers or both of them. The switching overvoltage and lightning intruding overvoltage are calculated to evaluate the feasibility of using one-column-varistor arresters in UHV substations. At the same time, the energy absorbed by and current flowing through the arresters, and the thermal stability of these one-column-varistor arresters are analyzed to ensure their safe operations. It is shown that conventional one-column-varistor arresters can be used for busbars and transformers in UHV substations to replace conventional four-column-varistor arresters and could highly reduce the construction cost of the UHV substation, but the safety of the substation will remain the same.

Locating corona discharges is essential for the safe operation and the reliability of smart grid. This paper proposed a novel method for corona discharge location based on tunneling magnetoresistive (TMR) sensors. A dual-axial TMR sensor device was designed to measure the vector magnetic field. The sensor’s responses to the corona discharge magnetic field have been compared with the results of standard probes and proved to be practicable. The location algorithm based on the vector magnetic field measurement results of sensor array indicated a relative error of approximately 10%, which was reasonable for the practical application. This method fully utilizes the merits of the sensors and provides a promising solution for corona discharge location.

Over recent years, there has been a growing interest in the field of energy harvesters and their applications across a wide range of areas. In the context of harvesting ambient stray magnetic energy, a magnetoelectric (ME) transducer based on piezoelectric transduction has attracted most scientific attention. Though the ME transducers based on the electromagnetic (EM) induction mechanism promises are highly efficient and much more easier to be integrated, research on this specific type of ME transducer has been scarcely reported. This paper presents the design, fabrication, and experimental results of a novel EM energy harvester. Unlike other EM harvesters that linearly vibrate, the proposed one operates in a rotatory mode, making use of a specially designed magnet array to convert the horizontal ac magnetic field into a vertical spinning magnetic field, as well as the printing coils to scavenge energy from the rotatory magnetic field. In this paper, the influence of the load, the applied magnetic field, and the magnet’s spatial arrangement are studied analytically, and the experimental results obtained by our fabricated prototype are consistent with the simulation results. The fabricated harvester prototype is able to generate 23.1 $\mu \text{W}$ under a 2 Oe magnetic field at a resonant frequency of 10 Hz, corresponding to a power density of $14.2~\mu \text{W}$ /cm3. Simulation and experimental results show that miniaturizing the harvester (i.e., reducing both the volume of magnet array and the area of printing coils) as well as increasing the coil turns can bring about a higher resonant frequency and a higher power density, which makes the micro-machined EM harvester a better fit for the ubiquitous 60 Hz ambient magnetic energy.

ZnO microvaristor/rubber composites with nonlinear conductive and dielectric properties were fabricated and investigated for the first time. The composites exhibit nonlinear conductive behaviors only when the filler concentration is above percolation threshold (39 vol%), but show nonlinear dielectric properties with various filler concentration (viz. 30–60 vol%). Both the nonlinear conductive and dielectric properties can be tuned by adjusting the filler concentration. Percolation threshold theory was utilized to explain the nonlinear electrical properties, and an internal barrier layer capacitor (IBLC) model was proposed to successfully explain the novel nonlinear dielectric properties, which demonstrates that the hole injection might be the key to the dramatic increase of the permittivity.

The aim of this study is to clarify the clinical implication and functional role of structure specific recognition protein 1 (SSRP1) in hepatocellular carcinoma (HCC) and explore the underlying mechanism of aberrant high expression of SSRP1 in cancers. In the present investigation, we validated that SSRP1 was upregulated in HCC samples. We also demonstrated that its upregulation was associated with several clinicopathologic features such as higher serum AFP level, larger tumor size, and higher T stage of HCC patients; and its high expression indicated shorter overall survival and faster recurrence. To investigate the role of SSRP1 in HCC progression, both loss- and gain-function models were established. We demonstrated that SSPR1 modulated both proliferation and metastasis of HCC cells in vitro and vivo. Furthermore, we demonstrated that SSRP1-modulated apoptosis process and its knockdown increased the sensitivity of HCC cells to doxorubicin, 5-Fluorouracil, and cisplatin. We also identified microRNA-497 (miR-497) as a posttranscriptional regulator of SSRP1. Ectopic expression of miR-497 inhibited 3'-untranslated-region-coupled luciferase activity and suppressed endogenous SSRP1 expression at both messenger RNA and protein levels. For the first time, we proved that SSRP1 upregulation contributed to HCC development and the tumor-suppressive miR-497 served as its negative regulator.

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.

This paper studied how to improve the high-impulse current discharge capability of ZnO varistors by doping with gallium oxide. In particular, the current–voltage characteristics under small and upturn current characteristics were examined. In the small current region, the gallium dopant is available to improve the surface state density and the potential barrier, which inhibits the leakage current from increasing and leads to the improvement of the stability of ZnO varistors in operation. In the upturn region, the gallium dopant makes the I–V curve shift right, so the nonlinearity region is extended and the impulse current discharge capability of ZnO varistors is greatly improved. High-performance ZnO varistor ceramics with optimal compositions were obtained under 0.42 mol% Ga 2 O 3 ; their nonlinearity coefficient and voltage gradient under 1 mA reached 80 and 432 V/mm, respectively. This finding is helpful for dramatically improving the protective effect of surge protection devices assembled with ZnO varistors as the core element in electrical systems and greatly increasing the safety of electrical systems.

The nonlinear ion flow field around ac–dc hybrid transmission lines due to corona varies with time. As the electric field and the space ions interact with each other, iterative algorithms, which include electric field calculation and ion density calculation, are usually used to simulate the ion flow field. In this paper, based on a pair of first-order partial differential equations of the ion densities, a time-domain method of characteristics is presented to calculate the ion densities analytically. Then, a time-domain iterative approach with the help of the method of characteristics is developed to calculate the ion flow field around ac–dc hybrid transmission lines. Because the electric field is also calculated analytically by accumulating all the contributions from the ions in the space and the charges on the surfaces of the conductors, almost all variables can be obtained via analytical formulas and no large-scale system of equations needs to be solved. The calculated results are in good agreement with the measured ones.

Lightning shielding failure accounts for the highest proportion of lightning accidents for transmission systems above 500 kV. The leader propagation model (LPM) was found to be effective in the analysis of lightning shielding failure of high-voltage transmission lines, especially for the ultrahigh voltage (UHV) transmission systems. However, it was generally inefficient to calculate the shielding failure rate by LPM, since the progress of lightning development must be simulated repeatedly, which is time-consuming, and no adaptive implementation of LPM has been reported. In this paper, adaptive strategies to accelerate the computation of shielding failure analysis by LPM were proposed, which include the adaptive time step control according to the electric field at the conductor surface, non-uniform lightning current sampling based on the lightning current amplitude probability distribution, and the adaptive lightning location sampling based on recursive adaptive Simpson’s method. The analysis results were validated by the field data of the UHV transmission line in Japan, and the efficiency of the adaptive strategies was shown by the shielding failure analysis of a typical 500 kV ac transmission line.

The accumulation of space charge in high voltage direct current cable will bring the insulation to failure; the addition of nanoparticles can markedly improve the space charge distribution characteristics inside the cable insulation, but particle agglomeration and cavitation lead to difficulty in controlling the properties of nanocomposites. In this paper, polypropylene (PP)/propylene-ethylene copolymer (PEC) and PP/ethylene-octene copolymer (EOC) blends were prepared by mechanical blending in order to improve both mechanical properties and space charge distribution. Dynamic mechanical thermal analysis shows that both blends have excellent mechanical properties for recyclable power cable. Pulsed electro-acoustic and thermally stimulated depolarization current tests illustrate that PP/EOC blends significantly decrease space charge accumulation and remarkably increase the trap density in the bulk compared with PP and PP/PEC blends. The increase of the trap density in PP/EOC blends can be explained as the result of the shallow traps introduced by the crystalline − amorphous interface existing in the boundaries of spherulites. The shallow traps can act as hopping sites to improve the transportation of space charges. © 2016 Society of Chemical Industry