Jun Hu

Tsinghua University, Peping, Beijing, China

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Publications (139)205.44 Total impact

  • Yao Zhou · Jun Hu · Bin Dang · Jinliang He
    [Show abstract] [Hide abstract] ABSTRACT: Polymer nanocomposite dielectrics always attract widespread attention in electrical and electronic field. Space charge suppression under direct current electric field is one of the key issues in developing high performance insulation materials. This paper reports a potential mechanism of space charge suppression in polypropylene/titanium oxide nanocomposites. Trap level distribution and space charge accumulation are obtained by thermally stimulated current and pulse electro-acoustic method, respectively. Micro morphology and structure of the nanocomposites are examined by differential scanning calorimetry, X-ray diffraction and positron annihilation lifetime spectroscopy. The results indicate that doping of titanium oxide introduces numerous shallow traps and reduces the number of deep traps, which significantly suppresses space charge accumulation and increases conductive current. The results can be explained that shallow traps, resulting from the interfaces between nanoparticles and polymer matrix and the interaction between nanoparticles and the crystalline/amorphous interfaces, could increase the charge carrier mobility and reduce potential barrier for charge carrier transport. This potential mechanism is of great importance to understand the space charge suppression in polymer nanocomposites and designing high performance nanodielectric materials.
    No preview · Article · May 2016 · RSC Advances
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    Kunjin Chen · Jun Hu · Jinliang He
    [Show abstract] [Hide abstract] ABSTRACT: With the development of smart grid, it is of increasing significance to identify and cope with various types of overvoltages, faults and power quality disturbances effectively and automatically. In this paper, a framework for overvoltage identification and classification based on sparse autoencoder is proposed. By using single-layer and stacked sparse autoencoder, dimensionality reduction and automatic feature extraction of ferroresonance overvoltage waveforms in power distribution systems are achieved as an example, which does not require feature engineering to produce a series of features. Classification of different ferroresonance modes is then implemented with a softmax classifier, and favorable classification results are obtained after parameters of feature extraction and classifier models are determined. Application of the proposed framework in smart grids is discussed. The proposed framework provides a brand new idea for establishing a smart identification and classification system for overvoltages, which can be generalized to classification of faults and power quality disturbances.
    Full-text · Article · Apr 2016 · IEEE Transactions on Smart Grid
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    Jinliang He · Chenlu Cheng · Jun Hu
    Full-text · Dataset · Apr 2016
  • [Show abstract] [Hide abstract] ABSTRACT: Dielectric polymer materials with high energy storage capability are highly desirable for use in both electric power and electronics industries. Previous studies have focused on developing polyvinylidene fluoride (PVDF)-based dielectric polymer materials with enhanced dielectric permittivity, but such nanocomposites also have a considerably decreased breakdown strength. In this study, we provide an effective strategy to considerably improve the breakdown strength of PVDF nanocomposites by introducing a small amount of functionalized MgO nanoparticles. The Weibull breakdown strength has been increased by 59% and the charge–discharge energy efficiency has also been considerably improved. This study's findings enable the design and development of advanced dielectric polymer nanocomposites with high breakdown strength and energy density for energy storage applications.
    No preview · Article · Apr 2016 · RSC Advances
  • Bin Dang · Jinliang He · Jun Hu · Yao Zhou
    [Show abstract] [Hide abstract] ABSTRACT: The accumulation of space charge in high voltage direct current (HVDC) cable will bring the insulation to failure, and the addition of nanoparticles can strongly 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 property and space charge distribution. Dynamic mechanical thermal analysis (DMTA) shows that both blends have excellent mechanical properties for recyclable power cable. Pulsed electro-acoustic (PEA) and thermally stimulated depolarization current (TSDC) tests illustrate that PP/EOC blends significantly decrease space charge accumulation and remarkably increase the trap density in the bulk than 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 interfaces existing in the boundaries of spherulites. The shadow traps can act as hopping sites to improve the transportation of space charges.
    No preview · Article · Apr 2016 · Polymer International
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    Jinliang He · Chenlu Cheng · Jun Hu
    [Show abstract] [Hide abstract] ABSTRACT: Researches on electrical degradation of double-Schottky barrier in ZnOvaristors are reviewed, aimed at the constitution of a full picture of universal degradation mechanism within the perspective of defect. Recent advances in study of ZnOmaterials by atomic-scale first-principles calculations are partly included and discussed, which brings to our attention distinct cognition on the native point defects and their profound impact on degradation.
    Full-text · Article · Mar 2016 · AIP Advances
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    Lei Gao · Xiao Yang · Jun Hu · Jinliang He
    Full-text · Dataset · Feb 2016
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    Lei Gao · Xiao Yang · Jun Hu · Jinliang He
    [Show abstract] [Hide abstract] ABSTRACT: 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.
    Full-text · Article · Feb 2016
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    [Show abstract] [Hide abstract] ABSTRACT: Epoxy resins blended with micro-sized alumina show more compact surface condition and exhibit lower light emission after modified in fluorinated atmosphere. Surface morphology reflected by atomic force microscope shows that the fluorinated surface layer can overlap alumina particles inlayed in the original surface and a smoother and more compact surface condition is generated. Thermally stimulated current test exhibits that surface fluorination is able to bring more shallow traps to surface states, and the trap amount increases with the extension of fluorinating time. The photon counting technique illustrates that the fluorinated surface has lower light emission which indicates better aging inhibition properties. Therefore, we believe that the surface fluorination technique may have potential significance in modifying epoxy based insulators used in high voltage applications.
    Full-text · Article · Feb 2016 · AIP Advances
  • [Show abstract] [Hide abstract] ABSTRACT: The present study examined the electrical properties of ZnO varistor ceramics co-doped with Ga2O3 and Al2O3, in particular, the current-voltage characteristics under small and intermediate currents and upturn characteristics under a large current. With increasing amounts of Ga2O3 dopant at a given Al2O3 concentration, both the threshold voltage in the small-current region and nonlinear coefficient of the varistor ceramics increased and then decreased; in contrast, the leakage current decreased and then increased. Moreover, ZnO varistor ceramics with low residual voltage ratio, high nonlinearity, and low leakage current were obtained under an optimal Ga concentration of 0.72 mol% while the Al additive content was fixed at 0.1 mol%. This novel finding will be helpful towards the manufacture of high-quality ZnO varistors.
    No preview · Article · Feb 2016 · Materials Letters
  • No preview · Article · Jan 2016 · IEEE Transactions on Magnetics
  • Fen Xue · Jun Hu · Shan Wang · Jinliang He
    No preview · Article · Jan 2016 · IEEE Magnetics Letters
  • No preview · Article · Jan 2016 · IEEE Transactions on Magnetics
  • [Show abstract] [Hide abstract] ABSTRACT: This paper deals with the electrical characteristics of rare-earth-doped ZnO varistor ceramics. Multiple donor dopants (Al3+, Ga3+, and Y3+) were employed to improve the comprehensive performance of ZnO varistor ceramics. The leakage current of rare-earth-doped ZnO varistor ceramics decreased noticeably with Ga2O3 dopants. The Ga3+ dopant occupies the defect sites of grain boundaries and increases the barrier potential of ZnO varistor ceramics, so the leakage current is effectively inhibited. Y2O3 is primarily located around the grains, which restrains ZnO grain growth, increasing the voltage gradient. The Al3+ goes into the lattices of ZnO grains, decreasing the grain resistance; thus, the residual voltage ratio can be controlled at low levels under a high impulse current. With the combined incorporation of Al3+, Ga3+, and Y3, excellent electrical properties of ZnO varistor ceramics can be acquired with a nonlinearity coefficient of 87, voltage gradient of 517 V/mm, leakage current of 0.96 μA/cm2, and residual voltage ratio of 1.60. These rare multiple donor dopants can aid in engineering high-quality ZnO varistors.
    No preview · Article · Jan 2016 · Journal of the American Ceramic Society
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    Bin Dang · Jinliang He · Jun Hu · Yao Zhou
    [Show abstract] [Hide abstract] ABSTRACT: Cross-linked polyethylene (XLPE) is a thermosetting material that cannot be recycled at the end of its lifetime. This study investigated the potential of syndiotactic polypropylene (sPP)/silica as an ecofriendly extruded insulation system for HVDC cables. We investigated the morphology, Fourier transform infrared, and thermal, thermomechanical, and electrical behaviors of sPP modified with 0.5–3% nanosilica. We found that the silica/sPP nanocomposite without cross-linking offered a suitable mechanical modulus at room temperature and sufficient intensity at high temperatures, and adding nanosilica modified by a silane coupling agent to the sPP resulted in significant DC resistivity and space charge improvement. The optimal nanosilica content in the sPP was determined by balancing the mechanical and thermomechanical characteristics and the DC resistivity. The sPP/silica nanocomposite reported here shows great potential as a candidate insulation material for future ecofriendly extruded HVDC cables.
    Full-text · Article · Dec 2015 · Journal of Nanomaterials
  • [Show abstract] [Hide abstract] ABSTRACT: 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% Ga2O3; 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.
    No preview · Article · Dec 2015
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    Full-text · Dataset · Nov 2015
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    Full-text · Dataset · Nov 2015
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    [Show abstract] [Hide abstract] ABSTRACT: Insulation performance of the dielectrics under extreme conditions always attracts widespread attention in electrical and electronic field. How to improve the high-temperature dielectric properties of insulation materials is one of the key issues in insulation system design of electrical devices. This paper studies the temperature-dependent corona resistance of polyimide (PI)/Al2O3 nanocomposite films under high-frequency square-wave pulse conditions. Extended corona resistant lifetime under high-temperature conditions is experimentally observed in the 2 wt% nanocomposite samples. The “thermal stabilization effect” is proposed to explain this phenomenon which attributes to a new kind of trap band caused by nanoparticles. This effect brings about superior space charge characteristics and corona resistance under high temperature with certain nano-doping concentration. The proposed theory is experimentally demonstrated by space charge analysis and thermally stimulated current (TSC) tests. This discovered effect is of profound significance on improving high-temperature dielectric properties of nanocomposites towards various applications.
    Full-text · Article · Nov 2015 · Scientific Reports
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    Lei Gao · Jinliang He · Jun Hu · Chao Wang
    Full-text · Dataset · Nov 2015

Publication Stats

715 Citations
205.44 Total Impact Points

Institutions

  • 2006-2016
    • Tsinghua University
      • • Department of Electronic Engineering
      • • School of Medicine
      • • Department of Electrical Engineering
      Peping, Beijing, China
  • 2008
    • Wuhan University
      Wu-han-shih, Hubei, China