Papers by Author: Hai Yun Jin

Abstract: The surface state of aramid fiber was modified by coupling agent to characterize the change of the state. The fiber / epoxy resin composites were prepared to study the mechanical and electrical properties and the internal mechanism of how different surface states affect. The results show that, after the treatment with the coupling agent, the surface roughness of the aramid fiber is increased，and the content of Si on the surface reach 5.8%, thus the surface activity is enhanced. At the same time, the treatment makes the properties of composites further improved. When the filling amount of aramid fiber reaches 30 strands, the tensile strength increase by 38.4% due to the coupling agent. In the test of two-layer samples, the breakdown field strength of the composites before and after treatment with coupling agent increased by 15.9% and 20.2%, respectively.Key words: aramid fiber; coupling agent; surface state; mechanical properties; electrical properties

Abstract: In order to solve the thermal aging problem of silicone rubber insulation layer of 220 kV integral prefabricated cable joints, the mass loss and thermal gravimetric (TG) were tested. The thermal aging mechanism of thermal degradation reaction of silicone rubber molecular chains was analyzed by gel content test and infrared spectrum test (IR). The results showed that the cross-linked network of the molecular chain structure gradually deteriorates, resulting in the increase of mass loss rate and the decrease of thermal stability. The results also showed that the increase of dual peak of differential thermal weight (DTG), the decrease of initial decomposition temperature and the remaining mass. With increasing aging temperature and aging time, the aging would be accelerated. These properties could reflect the degree of thermal aging of silicone rubber insulation layer. The results could also provide theoretical support for the preparation, operation and maintenance for silicone rubber cable joints.

Abstract: Epoxy resin composites filled with alumina (Al₂O₃) particles of different morphology and content were fabricated by vacuum casting method. Electric and thermal properties of the composites were tested at room temperature to investigate the influence of Al₂O₃ morphology on epoxy resin composites. Electrical tests demonstrated that, volume resistivity of epoxy resin composites filled with spherical Al₂O₃ was bigger than with spherical-like Al₂O₃, relative permittivity and dielectric loss of epoxy resin composites increased with increasing of Al₂O₃ content, the effect on dielectric properties of spherical-like Al₂O₃, which had larger specific surface areas, was larger than spherical Al₂O₃ for the same content of filler. Thermal conductivity tests proved that, at the same content, thermal conductivity of epoxy resin composites filled with spherical-like Al₂O₃ was higher than with spherical Al₂O₃. According to the Agari model, spherical-like Al₂O₃ particles were easier to form conducting pathways in epoxy resin composites than spherical Al₂O₃ particles, considering their matte edges.

Abstract: Uniform standard in the structural design for insulated tubular bus is not available both at China and abroad, and there are few reports about insulated tubular bus, which causes a waste of resources and even leads to grid failure. In this paper, epoxy/paper composites insulated tubular bus was investigated and a two-dimensional model was preferred in the simulation due to the axial symmetry of insulated tubular bus. The distribution of electric field and temperature in composite insulated materials were studied with the changes of the diameter/thickness of copper pipe and the thickness of insulation materials. According to the results simulation results, the structure of insulated tubular bus was optimized, the thickness of copper pipe conductor and insulation had been greatly reduced. Compared to the non-optimized initial structure, the amount of copper pipe conductor used for the optimized insulated tubular bus was reduced by 48%, the amount of insulation materials were reduced by 52.5%, and the current density of copper pipe conductor increased by 92.2%.

Abstract: The buried environment of cross-linked polyethylene (XPLE) cable is relatively severe, and some ones are even immersed in water directly. In this paper, an XLPE cable was soaked in foul water to simulate the cable’s actual water area environment, lasting for three years. The water content in the insulation layers of water-soaked cable was measured by infrared spectrometer and moisture analyzer, and the crystal morphology and physicochemical properties of the insulation layers were investigated by differential Scanning Calorimeter (DSC), scanning electron microscopy (SEM) and tensile testing technology. The results showed that a small amount of water did enter into the cable insulation owing to the increasing of hydroxyl (-OH) content, and followed being verified by moisture analyzer. The degree of crystallinity of water-soaked cable insulating material is also increased, and the mechanical properties were deteriorated.

Abstract: Cross-linked polyethylene (XLPE) as insulation material has been widely used in the manufacturing of medium and high voltage cables for its excellent physical, chemical, mechanical and electrical properties. However, as cable insulation, the XLPE will degradate under service conditions, such as thermal oxidative degradation, mechanical treatment, operating environment etc. In this paper, the closed cable loop had been heated for 7 days by induced current of 1000A, and several diagnostic measurements had been adopted to characterize the performance of XLPE. Firstly FTIR has been conducted on different bending degree cable samples in order to reveal the effect of mechanical treatment on the content changes which occur in XLPE insulation layers. DSC analysis showed the effect of cooling process on the shoulder melting peak temperatures. In the last part, microstructure of the insulation of high current bending XLPE cable was studied. The results showed that the properties of the bending cable after heating by the high current changed a lot and the degree of bending also has an effect on the performance of the cable.

Abstract: Porous SiAlON ceramics were fabricated by carbo-thermal reduction nitridation method using Fe₂O₃ as pore former. Particle size effects of Fe₂O₃ were reported in this paper. The results showed that composites were composed by SiAlON, AlN and Iron Silicon phases. The median pore diameter of Sialon was affected by the composition and particle size of Fe₂O₃. The fracture mode of this material was intergranular. With the increase of Fe₂O₃ additions, the porosity of this materials increased. The bending strength of this material was reversely proportional to Fe₂O₃ particle size. The maximum bending strength of Porous materials with 30wt.% Fe₂O₃ additions (with a porosity about 65% and the pore size is about 1μm) could reach 22 MPa. The porous Sialon ceramics with a smaller pore size exhibited a higher bending strength.

Abstract: Superhydrophobic surfaces have attracted much interest for its potential applications. In this study, the superhydrophobic aluminum surfaces were fabricated by method of chemical etching. Aluminum surfaces were firstly chemically etched by hydrochloric acid, and modified with stearic acid. The relationship between the etching time and the surface hydrophobicity was investigated. The contact angle and the sliding angle were tested, the results showed that with increasing etching time, the contact angle experienced a rise and then decrease, while the sliding angle dropped first and then started to climb. A maximum value of 152 degrees for the contact angle and a minimum value of 3 degrees for the sliding angle were obtained with etching time of 1 minute. The results indicated an ideal superhydrophobic property of the aluminum surfaces.

Abstract: The effects of Cr₂O₃ additions on the mechanical and electrical properties of alumina ceramics were investigated. The phase composition, organizational structure of ceramics were analyzed and observed using XRD and SEM. The results show that doping with small amount (<7wt.%) of Cr₂O₃ can improve the mechanical (15% for bending strength, 83% for Vickers hardness) and electrical properties (minimum resistivity 9.8 × 10¹²Ω·cm), but when doping amount above 7wt.% , these properties were decreased.

Abstract: Abstract. In this paper, the thermal expansion characteristics of epoxy resin/crepe paper composite insulation structure for high-voltage DC bushing were studied. The results showed that when temperature was lower than the glass transition temperature(Tg) of epoxy resin, coefficients of thermal expansion along axial and radial direction of the insulation structure increased with increasing temperature; When higher than Tg, with an increasing temperature, the CTE along radial direction of the structure increased-even larger than the pure epoxy, while axial decreased. Tg is obtained by DSC. The microstructure of high-voltage DC bushing was observed by polarizing microscope. On the basis of the above analysis, the different trend in thermal expansion characteristics may be resulted from the sample structure, fiber distribution of crepe paper and the movement of epoxy resin molecular chains.