Nano-composite Particles Synthesized by a Hydrogen Arc Plasma

Nano-composite particles can be synthesized by a hydrogen arc plasma method, which possesses the advantages of high productivity, controllable size distribution and low electric energy consumption comparing with conventional gas condensation method. With this method, not only the nanoparticles of metals and alloys, but also the nano-composite particles with shell structure can be synthesized. The microstructures, compositions and the formation mechanism of the nano composite particles were studied

Effect of temperature on electric-thermal properties of semiconductive shielding layer and insulation layer for high-voltage cable

A semi‐conductive shielding layer plays an important role in the uniform electric field for a high‐voltage cable.The electric‐thermal properties of the semi‐conductive layer and insulation layer directly affect the overall insulation performance of the cable.The physicochemical performances of semi‐conductive composites are firstly analysed herein.Furthermore,electric‐thermal properties of the semi‐conductive layer and insulation layer are discussed.The experimental results show that the thermal conductivity of the commercial semi‐conductive layer is about twice that of the insulation layer,owing to the effect of carbon black.The thermal expansion coefficient of the insulation layer rises from 1.86×10^(−4)/K at 25℃ to 3.20×10^(−4)/K at 90℃.By contrast,the semi‐conductive layer begins to slowly decline at a certain temperature,and decreases signif-icantly to 2.25×10^(−4)/K at 80℃,owing to the effect of ethylene‐vinyl acetate copolymer(EVA).The electrical experiments show that the resistivity of semi‐conductive composite gradually rises with an increase in temperature,and gradually declines with an increase in the carbon black content.The dc breakdown strength of the composite structure of the semi‐conductive layer/insulation layer decreases significantly with an increase in tem-perature,decreasing from 307 kV/mm at 25℃ to 203 kV/mm at 90℃.At four typical temperatures,the breakdown strength reaches the maximum value when the carbon black content is 25 phr.It is about 15%and 19%higher than carbon black contents of 20 and 30 phr.These findings have reference significance for high‐voltage cable breakdown fault analysis and material selection in cable design.

Research progress of semiconductive shielding layer of HVDC cable

As an indispensable part of high-voltage direct current(HVDC)cable,the semiconductive shielding layer plays the role of uniforming electric field in the cable.However,cable shielding materials>35 kV mainly rely on foreign imports in China,which belongs to the technical weak issues in the field of electrical materials.At present,there are few systematic reports on semiconductive shielding material of HVDC cable.In the work,the mechanisms of charge conduction and thermal conduction of semiconductive material have been introduced.Effect of raw material,carbon black content and the second conductive filler on the resistance characteristics of the semiconductive layer,the charge accumulation characteristics of the insulating layer and the interface characteristics have been studied.A kind of semiconductive layer as a high voltage terminal charge emission method has been proposed to study charge emission from the semiconducting layer to the insulation layer.This work can provide theoretical guidance for the research of semiconductive shielding materials.

Effect of graphene modified semi-conductive shielding layer on space charge accumulation in insulation layer for high-voltage direct current cable

Space charge accumulation in the insulation layer of high-voltage direct current(HVDC)cable is one of the key factors restricting the development of HVDC cable.The inner semi-conductive layer as an important structure of cable will affect the charge accumu-lation characteristics in the insulation layer.This work intends to explore the method of modifying the semi-conductive layer with graphene,to suppress charge accumulation in the insulation layer.First,the semi-conductive layer with different contents of Graphene(G)and carbon black(CB)are prepared.Second,the morphology and surface roughness of the cross section are analysed.Further,the effects of the semi-conductive layer on space charge accumulation of the insulation layer are studied by pulsed electro-acoustic method and thermal stimulation depolarisation current method.The experimental re-sults show that a moderate amount of graphene replacing CB can effectively reduce charge accumulation in the insulation layer and inhibit positive temperature coefficient(PTC)effect at the same time.The surface roughness of specimens decreases with the increase of G content from 0 to 3 phr(parts per hundreds of resin),when the CB content decreases from 25 to 10 phr,the surface roughness of specimen increases.The resistivity test shows that doping G can significantly inhibit the PTC effect of the semi-conductive layer.The volume resistivity of the semi-conductive layer decreases with the increase of G content and CB content.In addition,charge accumulation of the insulation layer rises and then drops under the action of the semi-conductive layer.

Effect of LiCoO_(2)on the positive temperature coefficient effect(PTC)properties of semiconductive composites and its ability to inhibit space charge injection

The semiconductive shield layer is between the conductive core and the insulation layer of high voltage direct current transmission cables and plays an important role in suppressing the accumulation of space charge in the insulation layer.Since the prevalent positive temperature coefficient effect(PTC)of the semiconducting layer leads to cable ageing and failure,this paper proposes the use of lithium cobaltate to modify the semiconducting shield to suppress its PTC effect and improve its ability to inhibit space charge injection.The ionic conductor LiCoO_(2)was prepared by the sol–gel method.LiCoO_(2)particles with particle sizes ranging from tens to hundreds of nanometres were obtained by ball milling.The prepared LiCoO_(2)was used as a filler to modify the carbon black(CB)/ethylene vinyl acetate copolymer(EVA)/low density polyethylene(LDPE)composites.After melt blending and moulding cross-linking,LiCoO_(2)/CB/EVA/LDPE semiconductive shielding specimens were successfully fabricated.Resistivity,Thermally Stimulated Depolarisation Currents(TSDC),and pulsed electroacoustic measurements were conducted for the prepared specimens.The PTC effect,which is common in polymer composites,was successfully suppressed,and the PTC strength was reduced by 17%.The resistivity of the semiconductive shielding layer was significantly reduced.The ability of the semiconducting shield to inhibit space charge injection from the conductive core to the insulation layer was significantly improved.When LiCoO_(2)content is 0.5 wt%,the semiconductive shielding layer has the best performance,and the space charge in the insulation layer was reduced by 70%compared to the undoped semiconducting shield.

The effect of a conductive polyaniline/carbon black composite on the performance of a semiconductive layer

In this study,conductive polyaniline(PANI)ribbons were introduced to a semi-conductive layer to improve the conductivity stability of the layer during thermal expansion and enhance its ability to inhibit charge injection into the insulating layer.To maximise the effect of PANI,PANI and carbon black(CB)were preformed into a uniformly dispersed composite,which was then added to the polymer matrix of the semiconductive layer.The experimental results show that the resistivity of the semi-conductive layer containing the PANI/CB composite is more stable during thermal expansion than that of the semiconductive layer only doped with CB.This is attributed to the conductive CB network being enhanced by the PANI ribbons.In addition,due to the unique conductivity mechanism and high dielectric constant of PANI,the semiconductive layer has a strong ability to inhibit space charge injection into the insulating layer.

DC breakdown characteristics of XLPE/BNNS nanocomposites considering BN nanosheet concentration,space charge and temperature

Breakdown failure in insulation material is one of the key problems that threaten the safe operation of high-voltage direct current cable.In this work,the effect of boron nitride nanosheets(BNNSs)concentration,space charge and temperature on DC breakdown strength have been explored.Cross-linked polyethylene(XLPE)/BNNS nanocomposites were prepared by the melt blending method,and the basic characteristics of nanoparticles and composite were characterised.The experimental results indicate that DC breakdown strength of nanocomposite can be effectively improved when a small amount of BN nanosheet is doped into the matrix.The breakdown strength of the sample reaches the maximum value of 407.52 kV/mm when BNNS content is 0.5 wt%,which is about 33%higher than that of pure XLPE.Further,the effect of space charge on the breakdown of nanocomposites has been studied by pre-injecting charges.For the samples with different BNNS contents,all the breakdown strength present ascending trend when the polarity of the applied voltage is the same as that of the pre-injected charges.Besides,it can be found that the breakdown strength of the XLPE/BNNSs composite decreases significantly at 50°C,which is due to more charge accumulation at 50°C.It reaches 2.06×10^(−8)C which increases by about 2.2 times than the room temperature.

Green carbonization of waste coffee grounds into porous C/Fe hybrids for broadband and high-efficiency microwave absorption

Recently great effort s have been focused on designing high-performance microwave absorbers using sustainable biomass resources,but there remains a lack of green and efficient fabrication methods.Herein,inspired by natural porous character of biomass waste,we demonstrated a green one-step route to convert waste coffee grounds into porous C/Fe hybrids,and further explored their potential applications for broadband and high-efficiency microwave absorption.In this design,the WCG-20-750(incorporated 20 wt%Fe(C_(5)H_(7)O_(2))_(3)catalyst and carbonized at 750℃)exhibited porous microstructure with the highest char yield of 55.45 wt%.Furthermore,the as-prepared C/Fe hybrids from WCG-20-750 displayed excellent microwave absorption performances.Typically,the minimum reflection loss(RL_(min))reached to-52.86 dB and the widest effective absorption bandwidth(EAB)was 6.40 GHz at the thickness of 3.0 mm.This work provides an economically viable and environmentally friendly strategy to convert biomass wastes into value-added microwave absorbers,ultimately making contributions to the upcycling of renewable biomass resources and the fostering of sustainable environment.

Effect of matrix resin components on properties of the semi-conductive shielding material for high-voltage cable

The semi-conductive shielding layer is an important part of the high-voltage cable,playing a role in uniform electric field and reducing the air gap at the interface.The overall performance of the cable is affected by the semi-conductive shielding layer with different base resin composition.The matrix resins of ethylene-vinyl acetate(EVA),ethylene-ethyl acrylate(EEA)and ethylene-butyl acrylate(EBA)were used to prepare the semi-conductive shielding materials of CB/EVA,CB/EEA and CB/EBA.The influences of different matrix resins on the chemical,electrical,thermal and mechanical properties of the shielding materials were investigated.The results show that CB has the best dispersion in EBA resin and the worst dispersion in EEA resin.The temperature in-flection points of CB/EVA,CB/EEA and CB/EBA shielding materials are 90°C,100°C and 110°C,respectively,and the CB/EBA shielding material has the lowest resistivity and the weakest positive temperature coefficient effect at room temperature.The thermal conductivity of all three matrix resins is smaller than that of the shielding material,the thermal conductivity of CB/EVA and CB/EBA shielding materials show a slow increase with temperature,and the CB/EEA shielding material is the least affected by the tem-perature.The mechanical properties of the three matrix resins and the three shielding materials are EBA>EVA>EEA,among them the stress of CB/EBA shielding material is 31.0 MPa and the strain is 570%.This work has important reference significance for the selection of shielding layer matrix resin and material formulation in engineering applications.