绝缘剂用量对铁硅铝软磁粉芯磁性能的影响

采用纳米氧化硅/环氧树脂复合包覆工艺,在铁硅铝粉末表面实现了均匀连续的氧化硅绝缘层包覆。通过调节氧化硅用量,制备了不同绝缘包覆量的铁硅铝软磁粉芯。研究了氧化硅绝缘包覆量对粉芯磁性能的影响,发现随着氧化硅绝缘包覆量的增加,粉芯的有效磁导率降低,直流偏置性能提高,而粉芯损耗在不同频率或不同磁通密度下呈现不同的变化规律。非铁磁性高电阻率氧化硅绝缘材料的加入稀释粉芯单位体积内的磁矩,增大退磁场,阻碍磁化,增大磁滞损耗,降低涡流损耗被认为是导致粉芯磁性能随氧化硅绝缘包覆量变化的物理根源。而不同绝缘包覆量粉芯磁滞损耗和涡流损耗在不同频率或不同磁通密度下的竞争决定了粉芯总损耗的变化规律。实验所制备的铁硅铝粉芯具有远优于常规商用60μ铁硅铝粉芯产品的直流偏置性能。

结合三维量测数据的绝缘子选型与评估方法

绝缘配置可以在综合降低线路设备外绝缘配置成本和防污维护成本的基础上,从根本上降低污闪事故的发生概率,完备的绝缘子数据能够为科学合理的绝缘配置与选型提供可靠的支持。本文提出了一种新的绝缘子数据选型与评估方法,结合绝缘子三维量测数据及防污闪关键影响因子,采用多条件选型与评估模式,实现了绝缘子快速选型,极大提高了绝缘配置的效率。

XLPE电缆绝缘热老化特性规律实验研究

目前石化企业高压电缆“老龄化”日益严重、运行风险逐年增大,热老化是影响电缆整体绝缘状态的重要因素。开展XLPE电缆绝缘材料制备实验和模拟热老化实验,获取了0~480 h的XLPE薄片老化试样;并分别开展介质损耗因数、极化指数和局部放电测量实验,得到关键绝缘特征量随绝缘热老化程度的特性规律。研究结果表明,介质损耗因数、极化指数随XLPE电缆绝缘老化过程分别近似呈指数规律增长、均匀增长,局部放电量随老化过程逐渐增大且放电趋于集中。研究结果对于探明XLPE电缆绝缘劣化特性规律及验证XLPE绝缘材料热老化机理具有指导意义。

基于线结构光视觉方法的绝缘子防污参数测量

提出了基于结构光视觉量测原理的绝缘子防污参数测量方法,采用非接触的测量方式高效地获取绝缘子带有结构光条影像,充分利用摄影测量、视觉量测技术和目标旋转体的几何结构特性,实现了变电站输变电设备带电工作状态下的绝缘子几何模型重建和防污参数量测。试验证明,该方法的自动化程度和精度可以满足绝缘子防污参数工程测量的要求,为变电设备调爬、带电水冲洗等防污工作的开展提供高精度的数据服务。

Measurement Module for Young for Thermal Insulation Composite Polymeric

To analyze the feasibility of application of composite material as the insulating material, it is necessary to have knowledge of some of its mechanical properties. An insulating material may suffer from the most different efforts, but the major applications suggest mechanical bending and compression tests because the insulation can be applied on roofs of homes, liners similar to, in the form of plates. Thus, the product is continually flexed. When the material is used on a floor, it suffers constant compressions over its use. For tests performed in this study, we used the ASTM D695-96 for compression, an example of literature. Using such a standard test, specimens were produced for compression test, with specimens made of cylindrical shapes, respecting the condition that the height of the specimen corresponds to twice the diameter of the base. Polyurethane castor without charge vermiculite and mass loads of 10%, 15% and 20% matrix： four specimens for each type of material were produced. The composites were tested in a universal testing machine at a speed of 2 mm/s. The results are average values of four test samples, and initially show the behavior of castor oil polyurethane during the compression test, which is detailed in the stress versus strain curve. The achieved results are promising, and detailed in this paper.

Light Weight Insulating Material Prepared from Rice Husk

Pakistan is at 12th number in the rank of rice production countries. Along with the production of 4,500 thousand metric tons of rice enormous quantity of rice husk is left as waste. Light weight thermal insulating material was prepared from rice husk. Epoxy resin was used as a binder and was mixed with rice husk to give it strength, the sample was compressed at 7000 psi to produce cylindrical shape block. The thermal conductivity of the sample A, B, C and D of thickness 1, 2, 3 and 4 cm respectively was measured 0.0241, 0.0240, 0.239 and 0.0219 watts/m-k, which was lower than the common mortar by 51.74%, therefore it could be used in buildings and roof as an insulating material. This would be a suitable alternative which would not only save energy but also solve the environmental disposal problems as well. The results are very promising and we hope insulation material prepared would be useable in hot climate regions like Pakistan in buildings to prevent heat transfer.

Tunneling Conductance in Quantum-Wire/Ferromagnetic-Insulator/d-Wave Superconductor Junction

We have studied the quasiparticle transport in quantum-wire /ferromagnetic-insulator/d wave super- conductor Junction （q/FI/d） in the framework of the Blonder-Tinkham-Klapwijk model. We calculate the tunneling conductance in q/FI/d as a function of the bias voltage at zero temperature and finite temperature based on Bogoliubov- de Gennes equations. Different from the case in normal-metal/insulator/d wave superconductor Junctions, the zero-bias conductance peaks vanish for the single-mode case. The tunneling conductance spectra depend on the magnitude of the exchange interaction at the ferromagnetic-insulator.

Classification of Topological Insulators with Time-Reversal and Inversion Symmetry

In this paper, we find that topological insulators with time-reversal symmetry and inversion symmetry featuring two-dimensional quantum spin Hall （QSH） state can be divided into 16 classes, which are characterized by four Z2 topological variables ζk =0, 1 at four points with high symmetry in the Brillouin zone. We obtain the corresponding edge states for each one of these sixteen classes of QSHs. In addition, it is predicted that massless fermionic excitations appear at the quantum phase transition between different QSH states. In the end, we also briefly discuss the threedimensional case.

Investigations on Tracking and Erosion Resistance of Nano Silicone Composite for High Voltage Outdoor Insulation

In recent times, silicone rubber insulating material is used for power transmission line and substation insulation applications. In the present work, tracking and erosion resistance of the micro size filled and nano size filled silicone rubber material has been studied under the AC voltage, with ammonium chloride as a contaminant, as per IEC 60587 test procedures. The characteristic changes in the tracking resistance of the micro size and nano size filled specimens are analyzed through leakage current measurement. Comparative Tracking Index （CTI） is also evaluated in order to understand the relative behavior of solid electrical insulating material with regard to their susceptibility to surface tracking. Trend followed by the fundamental, third harmonic and fifth harmonic components of the leakage current during the tracking study are analyzed using moving average current technique. It is observed that the harmonic components of leakage current show good correlation with the tracking and erosion resistance of the material. It is noticed that 5 % wt ofnano size filler gives similar performance to that of 30 % wt of micro size filler in silicone composites.

Thermal Insulation Distribution Pattern of Layered Clothing Ensemble

With a thermal manikin, the distribution pattern of thermal insulation in multi-layered clothing ensemble is studied. It is found that the thermal insulation of multi-layered clothing ensemble has certain statistical relationship with the thermal insulation of each layer, and the prediction equation has been established.

A LS-SVM （Least Squares Support Vector Machines） Approach for Predicting Critical Flashover Voltage of Polluted Insulators

LS-SVM （least squares support vector machines） are a class of kemel machines emphasizing on primal-dual aspects in a constrained optimization framework. LS-SVMs aim at extending methodologies typical of classical support vector machines for problems beyond classification and regression. This paper describes a methodology that was developed for the prediction of the critical flashover voltage of polluted insulators by using a LS-SVM. The methodology uses as input variables characteristics of the insulator such as diameter, height, creepage distance, form factor and equivalent salt deposit density. The estimation offlashover performance of polluted insulators is based on field experience and laboratory tests are invaluable as they significantly reduce the time and labour involved in insulators design and selection. The majority of the variables to be predicted are dependent upon several independent variables. The results from this work are useful to predict the contamination severity, critical flashover voltage as a function of contamination severity, arc length, and especially to predict the flashover voltage. The validity of the approach was examined by testing several insulators with different geometries. Moreover, the performance of the proposed approach with other intelligence method based on ANN （artificial neural networks） is compared. It can be concluded that the LS-SVM approach has better generalization ability that assist the measurement and monitoring of contamination severity, flashover voltage and leakage current.

Group 14 element-based non-centrosymmetric quantum spin Hall insulators with large bulk gap

To date, a number of two-dimensional （2D） topological insulators （TIs） have been realized in Group 14 elemental honeycomb lattices, but all are inversionsymmetric. Here, based on first-principles calculations, we predict a new family of 2D inversion-asymmetric TIs with sizeable bulk gaps from 105 meV to 284 meV, in X2-GeSn （X = H, F, Cl, Br, I） monolayers, making them in principle suitable for room-temperature applications. The nontrivial topological characteristics of inverted band orders are identified in pristine X2-GeSn with X = （F, Cl, Br, I）, whereas H2-GeSn undergoes a nontrivial band inversion at 8% lattice expansion. Topologically protected edge states are identified in X2-GeSn with X = （F, Cl, Br, I）, as well as in strained H2-GeSn. More importantly, the edges of these systems, which exhibit single-Dirac-cone characteristics located exactly in the middle of their bulk band gaps, are ideal for dissipationless transport. Thus, Group 14 elemental honeycomb lattices provide a fascinating playground for the manipulation of quantum states.

Study of partial discharge characteristics at repetitive square voltages based on UHF method

Due to overvoltage produced by inverter output,inverter-fed motor insulation systems often experience fast electrical aging process,especially when partial discharge(PD) is incepted.Before putting into use,the PD detection should be performed on inverter-fed motors at repetitive square voltages to avoid the PD caused insulation deterioration when the motors are collected to inverters having specific characteristics.However,unlike PD tests at AC/DC voltages proposed in IEC 60270,the PD detection at repetitive square voltages is much more complex because of serious interference generated by impulse generator.To solve the problem,ultra-high frequency(UHF) method seems recommendable for its preferable signal-to-noise ratio(SNR).The chief aim of this study is to investigate PD pulse and statistical characteristics of turn-to-turn insulation for inverter-fed traction motors.A square-shaped Archimedes antenna,specially designed for the PD detection at repetitive square voltages of fast rise times,was used to perform PD tests on turn-to-turn insulation models.Time and frequency analysis results indicate that energy component of generator disturbance and PD pulses are mainly distributed in the 0-0.5 GHz and 0.6-1.5 GHz range,respectively.Based on the results,suitable filter was designed for power disturbance suppression.Additionally,resorting to the sensor unit(i.e.antenna and filter) and the PD test system,the PD statistical features at square voltages of different frequencies were obtained.Experimental results show that higher frequency will give rise,statistically,to PD of lower magnitudes distributing at smaller phases.A reasonable interpretation of this phenomenon was presented.Lastly,according to the PD statistical features,some suggestions for the PD detection system design,generator parameter optimization and the PD pulse extracting were given.The results of this work would be beneficial to the increase of the sensitivity when performing the PD detection on insulation systems for inverter-fed motors at repetitive square voltages and thus,improving the reliability of inverter-fed motors.

Demonstration of topological wireless power transfer

Recent advances in non-radiative wireless power transfer(WPT)technique essentially relying on magnetic resonance and near-field coupling have successfully enabled a wide range of applications.However,WPT systems based on double resonators are severely limited to short-or mid-range distance,due to the deteriorating efficiency and power with long transfer distance.WPT systems based on multi-relay resonators can overcome this problem,which,however,suffer from sensitivity to perturbations and fabrication imperfections.Here,we experimentally demonstrate a concept of topological wireless power transfer(TWPT),where energy is transferred efficiently via the near-field coupling between two topological edge states localized at the ends of a one-dimensional radiowave topological insulator.Such a TWPT system can be modelled as a parity-time-symmetric Su-Schrieffer-Heeger(SSH)chain with complex boundary potentials.Besides,the coil configurations are judiciously designed,which significantly suppress the unwanted cross-couplings between nonadjacent coils that could break the chiral symmetry of the SSH chain.By tuning the inter-and intra-cell coupling strengths,we theoretically and experimentally demonstrate high energy transfer efficiency near the exceptional point of the topological edge states,even in the presence of disorder.The combination of topological metamaterials,non-Hermitian physics,and WPT techniques could promise a variety of robust,efficient WPT applications over long distances in electronics,transportation,and industry.

Quantum transport in topological insulator hybrid structures-A combination of topological insulator and superconductor

In this paper,a brief review of the history of topological insulators is given.After that,electronic transport experiments in topological insulator-superconductor hybrid structures,including experimental methods,physical properties and seemingly contradictory observations are discussed.Additionally,some new topological insulator hybrid structures are proposed.

Multi-dimensional wave steering with higher-order topological phononic crystal

The recent discovery and realizations of higher-order topological insulators enrich the fundamental studies on topological phases.Here,we report three-dimensional(3D)wave-steering capabilities enabled by topological boundary states at three different orders in a 3D phononic crystal with nontrivial bulk topology originated from the synergy of mirror symmetry of the unit cell and a non-symmorphic glide symmetry of the lattice.The multitude of topological states brings diverse possibilities of wave manipulations.Through judicious engineering of the boundary modes,we experimentally demonstrate two functionalities at different dimensions:2D negative refraction of sound wave enabled by a firstorder topological surface state with negative dispersion,and a 3D acoustic interferometer leveraging on second-order topological hinge states.Our work showcases that topological modes at different orders promise diverse wave steering applications across different dimensions.

In situ Raman spectroscopy of topological insulator Bi2Te3 films with varying thickness

Topological insulators （TIs） are a new state of quantum matter with a band gap in bulk and conducting surface states. In this work, the Raman spectra of topological insulator Bi2Te3 films prepared by molecular beam epitaxy （MBE） have been measured by an in situ ultrahigh vacuum （UHV）-MBE-Raman spectroscopy system. When the thickness of Bi2Te3 films decreases from 40 quintuple-layers （QL） to 1 QL, the spectral characteristics of some Raman modes appearing in bulk Bi2Te3 vary and a new vibrational mode appears, which has not been reported in previous studies and might be related to quantum size effects and symmetry breaking. In addition, an obvious change was observed at 3 QL when a Dirac cone formed. These results offer some new information about the novel quantum states of TIs.

Assessment of High-Frequency Performance Limits of Graphene Field-Effect Transistors

High frequency performance limits of graphene field-effect transistors （FETs） down to a channel length of 20 nm have been examined by using self-consistent quantum simulations. The results indicate that although Klein band-to-band tunneling is significant for sub-100 nm graphene FETs, it is possible to achieve a good transconductance and ballistic on-off ratio larger than 3 even at a channel length of 20 nm. At a channel length of 20 nm, the intrinsic cut-off frequency remains at a few THz for various gate insulator thickness values, but a thin gate insulator is necessary for a good transconductance and smaller degradation of cut-off frequency in the presence of parasitic capacitance. The intrinsic cut-off frequency is close to the LC characteristic frequency set by graphene kinetic inductance （L） and quantum capacitance （C）, which is about 100 GHz-um divided by the gate length.

Topological Insulators in α-Graphyne

In this paper, we investigate topological phases of a-graphyne with tight-binding method. By calculating the topological invariant Z2 and the edge states, we identify topological insulators. We present the phase diagrams of a-graphyne with different filling fractions as a function of spin-orbit interaction and the nearest-neighbor hopping energy. We find there exist topological insulators in a-graphyne. We analyze and discuss the characteristics of topological phases of a-graphyne.

Three-dimensional topological insulators:A review on host materials

In recent years,three-dimensional topological insulators(3DTI) as a novel state of quantum matter have become a hot topic in the fields of condensed matter physics and materials sciences.To fulfill many spectacularly novel quantum phenomena predicted in 3DTI,real host materials are of crucial importance.In this review paper,we first introduce general methods of searching for new 3DTI based on the density-functional theory.Then,we review the recent progress on materials realization of 3DTI including simple elements,binary compounds,ternary compounds,and quaternary compounds.In these potential host materials,some of them have already been confirmed by experiments while the others are not yet.The 3DTI discussed here does not contain the materials with strong electron-electron correlation.Lastly,we give a brief summary and some outlooks in further studies.