Co-reporter:Xiaolei Zhao, Xiao Yang, Qi Li, Jinliang He, Jun Hu
Composites Science and Technology 2017 Volume 150(Volume 150) pp:
Publication Date(Web):29 September 2017
DOI:10.1016/j.compscitech.2017.07.025
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.
Co-reporter:Yao Zhou, Jun Hu, Bin Dang and Jinliang He
RSC Advances 2016 vol. 6(Issue 54) pp:48720-48727
Publication Date(Web):09 May 2016
DOI:10.1039/C6RA04868D
Polymer nanocomposite dielectrics always attract widespread attention in electrical and electronic fields. 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 pulsed electro-acoustic method, respectively. The 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 by the fact 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 in designing high performance nanodielectric materials.
Co-reporter:Hongfeng Zhao, Jinliang He, Jun Hu, Shuiming Chen, Qingyun Xie
Materials Letters 2016 Volume 164() pp:80-83
Publication Date(Web):1 February 2016
DOI:10.1016/j.matlet.2015.10.070
•ZnO varistor ceramics co-doped with Al2O3 and Ga2O3.•Al additive decreases the residual voltage under high currents.•Ga-doping increases the barrier potential and further reduces the grain resistance.•Optimal Ga additive concentration suggested as 0.72 mol%.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.
Co-reporter:Lei Gao, Xiao Yang, Jun Hu, Jinliang He
Materials Letters 2016 Volume 171() pp:1-4
Publication Date(Web):15 May 2016
DOI:10.1016/j.matlet.2016.02.016
•Composites with nonlinear conductive and dielectric properties are fabricated.•Composites exhibit nonlinear conductivity with high filler concentration (>39 vol%).•Composites also exhibit nonlinear dielectric properties with various filler concentration.•An internal barrier layer capacitor model is proposed to explain the mechanism.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.
Co-reporter:Yao Zhou;Jun Hu ;Bin Dang
Journal of Applied Polymer Science 2016 Volume 133( Issue 1) pp:
Publication Date(Web):
DOI:10.1002/app.42863
ABSTRACT
Polypropylene (PP)/polyolefin elastomer (POE) blends and MgO/PP/POE nanocomposites were fabricated by melt blending. The morphology, mechanical, and electrical properties of the nanocomposites were investigated. Scanning electron microscopy showed that the surface-modified MgO nanoparticles were well dispersed in the polymer matrix at low loadings of less than 3 phr. X-ray diffraction demonstrated that the crystalline phases of PP in the composites were changed and that the β phase significantly increased. An examination of the electrical properties revealed that the direct-current (dc) electric breakdown strength and space-charge suppression effect were remarkably improved by the introduction of the surface-modified MgO nanoparticles. In addition, obvious enhancements in the tensile modulus and strength were obtained as a result of the synergistic toughening of the POE and MgO nanoparticles. Thus, MgO/PP/POE nanocomposites with enhanced mechanical and electrical properties have great potential to be used as recyclable insulation materials for high-voltage dc cables with large transmission capacities and high operating temperatures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 132, 42863.
Co-reporter:Bin Dang;Jun Hu ;Yao Zhou
Polymer International 2016 Volume 65( Issue 4) pp:371-379
Publication Date(Web):
DOI:10.1002/pi.5063
Abstract
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
Co-reporter:Simin Peng, Bin Dang, Yao Zhou, Jun Hu, and Jinliang He
The Journal of Physical Chemistry C 2016 Volume 120(Issue 43) pp:24754-24761
Publication Date(Web):October 18, 2016
DOI:10.1021/acs.jpcc.6b07408
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 with respect to the results of the volume conductivity measurement. It is believed that this study would provide an important hint to the research of the interface between nanoparticles and the polymer matrix in future research.
Co-reporter:Lei Gao, Jinliang He, Jun Hu, and Chao Wang
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 45) pp:25546
Publication Date(Web):October 28, 2015
DOI:10.1021/acsami.5b09121
Microcapsule-based self-healing polymer materials are highly desirable because they can heal large-volume cracks without changing the original chemical structures of polymers. However, they are limited by processing difficulties and inhomogeneous distributions of two components. Herein, we report a one-component photoresponsive self-healing polymer composite with photoabsorbing hybrid microcapsules (PAHM), which gives the microcapsules photoabsorbing properties by introducing nano-TiO2 particles as photoabsorbing and emulsified agents in the poly(urea-formaldehyde)/TiO2 hybrid shells. Upon mechanical damage and then exposure to light, the photoresponsive healing agents in the cracks will be solidified to allow for self-healing, while the healing agents in the unbroken PAHM will be protected and remain unreacted, which endows this photoresponsive microcapsule-based self-healing composite with self-healing properties like those found in the conventional two-component microcapsule-based systems. Given the universality of this hybrid polymerization method, incorporation of the photoabsorbing particles to conventional polymer shells may further broaden the scope of applications of these widely used materials.Keywords: coating; microcapsule; photoabsorbing; photoresponsive; self-healing
Co-reporter:Xiao Yang;Jun Hu
Journal of Applied Polymer Science 2015 Volume 132( Issue 40) pp:
Publication Date(Web):
DOI:10.1002/app.42645
ABSTRACT
Silicone composite filled with zinc oxide microvaristors possesses excellent nonlinear conducting behavior as ZnO varistor does. For better adjusting the composite's electrical behavior to satisfy the practical field-grading requirement, this article studied the influence of ZnO filler's property on the nonlinearity of the composite. Several groups of ZnO-silicone composite samples in different filler volume fraction and filler diameter were prepared, the measured J-E characteristics show that the percolation threshold of ZnO-silicone composite is around 35%, above which the composites present reliable nonlinear behavior. The switching voltage of the composite exhibits a considerable decrease as filler's diameter increases or filler's volume fraction increases, while the nonlinear coefficient remains stable. Moreover, filler's size also has a little influence on composite's percolation limit. The conclusion above fits very well with the theory of the conducting composites and percolation process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42645.
Co-reporter:FengChao Luo;Jun Hu;YuanHua Lin
Science China Technological Sciences 2012 Volume 55( Issue 4) pp:879-882
Publication Date(Web):2012 April
DOI:10.1007/s11431-011-4738-9
Microcontact measurement is employed to locally investigate the electric and dielectric properties of individual grains and grain boundaries in CaCu3Ti4O12 ceramic. The measurements give more detail of the impedance spectroscopy, capacitance, and I–V characteristics of the microstructure, and will help with further understanding of the mechanism of the electric and dielectric properties of CaCu3Ti4O12 ceramics.
Co-reporter:Jun Liu, Jinliang He, Jun Hu, Wangcheng Long, Fengchao Luo
Materials Chemistry and Physics 2011 Volume 125(1–2) pp:9-11
Publication Date(Web):1 January 2011
DOI:10.1016/j.matchemphys.2010.09.023
The statistical AC ageing characteristics of single grain boundaries of ZnO varistor were investigated in this paper using the microcontact measurement method. ZnO varistor sample deposited with micro-electrodes was degraded under the ageing stress of 0.85 V1mA at 135 °C. The electrical properties of 100 grain boundaries were measured after ageing with different time. The results indicate that the distribution of nonlinear coefficients concentrates to the lower region and the leakage current gradually increases in the ageing process. Meanwhile, more grain boundaries with lower breakdown voltage emerge as the ageing time increases, which means that the nonlinearities of these grain boundaries become weak.Graphical abstractResearch highlights▶ The statistical ageing behavior of single grain boundaries. ▶ The distribution of nonlinear coefficients concentrates to the lower region. ▶ The leakage currents of grain boundaries continuously increase.
Co-reporter:Jinliang He, Jun Liu, Jun Hu, Wangcheng Long
Materials Letters 2011 Volume 65(17–18) pp:2595-2597
Publication Date(Web):September 2011
DOI:10.1016/j.matlet.2011.06.022
In this paper, AC ageing characteristics of high voltage gradient ZnO varistors doped with different Y2O3 concentration were investigated. The voltage gradient of these samples is markedly improved by increasing Y2O3 content, however, the nonlinear coefficient decreases and the leakage current increases at the same time. Y2O3-doped ZnO samples exhibit lower stability under accelerated AC ageing stress of 0.85 V1mA/135 °C/168 h, compared with samples without Y2O3. Double-Schottky barrier(DSB) parameters before and after ageing tests indicate that the decrease of barrier height for traditional sample is less than that for high voltage gradient sample, which should be ascribed to its slight variation in the interface state density.
Co-reporter:Jun Liu;Jun Hu;WangCheng Long
Science China Technological Sciences 2011 Volume 54( Issue 2) pp:375-378
Publication Date(Web):2011 February
DOI:10.1007/s11431-010-4216-9
In order to investigate the influence of sintering temperature on the Schottky barrier and bulk electron traps of ZnO varistors, ZnO-Bi2O3 based varistor ceramic samples were sintered at 1000, 1100, 1200 and 1300°C, respectively. The measured results indicate that the sample sintered at 1300°C possesses the lowest voltage gradient and nonlinear coefficient, compared with other samples. The barrier height of the samples decreased as the sintering temperature increased, which resulted in the deterioration of nonlinearity. Furthermore, two bulk electron traps determined by admittance spectroscopy were generally independent of sintering temperature, which indicated that these two traps might originate from the intrinsic defects in ZnO lattice.
Co-reporter:Wangcheng Long, Jun Hu, Jun Liu, Jinliang He
Materials Letters 2010 Volume 64(Issue 9) pp:1081-1084
Publication Date(Web):15 May 2010
DOI:10.1016/j.matlet.2010.02.019
The effects of cobalt additive on the electrical characteristics of the Al-doped ZnO varistors are studied in this paper. The current–voltage characteristics of the varistor samples have been investigated in a range from small to large current. With the amount of the doped cobalt increased, the leakage currents of the Al-doped ZnO varistors are inhibited, and their nonlinear coefficients increase remarkably as well. In addition, their breakdown electric fields increase in a small extent and their residual voltage ratios change slightly. Furthermore, the donor densities and the barrier heights of samples decrease with the cobalt content increased. The XRD patterns show that the Bi-rich phase and the willemite phase vary obviously in the varistor samples with various content of cobalt additive.
Co-reporter:Mohamed Nayel, Zhao Jie, Jinliang He
Journal of Electrostatics 2010 Volume 68(Issue 5) pp:439-444
Publication Date(Web):October 2010
DOI:10.1016/j.elstat.2010.06.005
This paper studies different parameters affecting a lightning stroke to a horizontal conductor. An electromagnetic model has been constructed to consider the influences of different lightning and horizontal conductor parameters and ambient conditions on the lateral striking distance. The results show that lightning leader parameters, horizontal conductor voltage, horizontal conductor height, and ground slope have a series effect on the lateral striking distance. Based on the results, recommendations are made to decrease the lightning stroke to the horizontal conductor.
Co-reporter:BaoPing Zhang;Rong Zeng
Science China Technological Sciences 2010 Volume 53( Issue 4) pp:918-921
Publication Date(Web):2010 April
DOI:10.1007/s11431-010-0114-4
By using X-ray film imaging technology, a phenomenon of discontinuous ionization was observed in the inhomogeneous soil around the grounding electrode on which a surge voltage was applied. A simplified two-phase solid-gas model was built to study the electric field distribution in the soil to explain the discontinuous ionization phenomenon. Analysis showed the differences of the dielectric properties, the shapes and sizes of soil particles can cause discontinuous ionization in the soil.
Co-reporter:JinLiang He;Jun Hu;YuanHua Lin
Science China Technological Sciences 2008 Volume 51( Issue 6) pp:693-701
Publication Date(Web):2008 June
DOI:10.1007/s11431-008-0085-x
The surge arrester of 1000 kV gas-insulated substation (GIS) needs ZnO varistor with high voltage gradient to effectively improve the potential distribution along ZnO varistor column inside the metal-oxide surge arresters. In this paper, the electrical and structural parameters of ZnO varistors are changed by doping with some rare-earth oxides, and the mechanism which leads these changes is discussed. When rare-earth oxide additives are added into ZnO varistors, the growing speed is slowed down due to the stabilization of the new spinel phases formed in the grain-boundary by rare-earth oxide additives, then the size of ZnO grains is smaller, and the voltage gradient of varistor increases obviously. By adding suitable amount of oxides of metal Co and Mn, the leakage current can be effectively decreased and the nonlinearity coefficient increased. The novel ZnO varistor samples sintered with the optimal additives have a voltage gradient of 492 V/mm, and the nonlinearity coefficient of 76, but their leakage currents are only 1 μA.
Co-reporter:Xiao Zhang, Zhanqing Yu, Jinliang He, Yunchao Wang, Rong Zeng
Electric Power Systems Research (June 2017) Volume 147() pp:302-309
Publication Date(Web):1 June 2017
DOI:10.1016/j.epsr.2016.05.038
•Artificial short circuit experiment is conducted on an operating ±800 kV system.•Broadband impedances and stray parameters of the major UHVDC equipment are measured.•The wideband frequency transfer characteristics of converting system are investigated.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.
Co-reporter:Jinliang He, Shanqiang Gu, Rong Zeng, Zhanqing Yu, Bo Zhang
Electric Power Systems Research (December 2011) Volume 81(Issue 12) pp:2066-2073
Publication Date(Web):1 December 2011
DOI:10.1016/j.epsr.2011.07.019
Flashovers due to lightning, pollution and other factors frequently generate long ac arcs along the surfaces of insulator strings on overhead transmission lines; they cause great damage to insulators. Based on the motion characteristics of long ac arcs obtained from experiments, this paper presents the propagation models of the motion processes of long ac arcs, these simulations are important to design suitable parallel arc horns to protect insulator strings. The simulation models include the spatial model, the temporal model of a long ac arc, and the motion simulation models of an arc root and an arc column. The spatial model discretizes a long arc to current elements; the temporal model is proposed to consider the motion mode of a current element; and the motion simulation models of an arc root and an arc column describe the motion processes of an arc root and a column, respectively. At last, numerical simulations and corresponding experiments of long ac arcs along the surfaces of insulator strings of overhead transmission lines are compared. Both of them show a similar motion trend.Highlights► The motion characteristics of long ac arcs based on experiments are summarized, especially the relationships between the length of an anode arc root and the arc current, and between a cathode arc root and the arc current are presented. ► The paper presents the propagation models of the motion processes of long ac arcs, including the spatial model discretizing a long arc to current elements, the temporal model considering the motion mode of a current element, the motion simulation models of an arc root and an arc column describing the motion processes of an arc root and an column a spatial model, are proposed. ► The motion processes of long ac arcs along the surfaces of insulator strings of overhead transmission lines are proposed from experiments. ► The numerical simulations of long ac arcs along the surfaces of insulator strings of overhead transmission lines, which have a similar motion trend with the corresponding experiments, are verified.
Co-reporter:Jinliang He, Xi Wang, Rong Zeng, Xiangyang Peng
Electric Power Systems Research (April 2012) Volume 85() pp:44-49
Publication Date(Web):1 April 2012
DOI:10.1016/j.epsr.2011.07.007
The impulse breakdown characteristic of soil is significant for evaluating the lightning trip-out rate of transmission lines. Firstly, this paper examined the impulse breakdown delay characteristics of soil through considerable experiments. Then the influence of the impulse breakdown delay phenomenon of soil on the lightning protection characteristics of transmission lines with different rated voltages is analyzed through the numerical calculation. Based on the results, the lightning electromagnetic transient process of transmission line considering the impulse breakdown delay was discussed. The analysis results indicate that the lightning withstand level has a decreasing trend with the increase of the soil impulse breakdown delay. The influence of the impulse breakdown delay on the lightning protection characteristics of transmission lines become weaker as the rated voltage level of transmission line increases.Highlights► Impulse breakdown delay characteristics of soil obtained from considerable experiments. ► Impulse breakdown delay of soil influences lightning protection characteristics of transmission lines. ► Lightning electromagnetic transient process of transmission line considering the impulse breakdown delay. ► Lightning withstand level decreases with soil impulse breakdown delay increasing.
Co-reporter:Jinliang He, Vladimir Rakov, Daohong Wang, Pao K. Wang
Atmospheric Research (28 July 2013) Volumes 129–130() pp:33
Publication Date(Web):28 July 2013
DOI:10.1016/j.atmosres.2013.05.005
![Poly[(5,7-dihydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c']dipyrrole-2,6(1H,3H)-diyl)-1,4-phenyleneoxy-1,4-phenylene]](http://img.cochemist.com/ccimg/25100/25036-53-7.png)
![Poly[(5,7-dihydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c']dipyrrole-2,6(1H,3H)-diyl)-1,4-phenyleneoxy-1,4-phenylene]](http://img.cochemist.com/ccimg/25100/25036-53-7_b.png)
