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Influence mechanism of side group types on the macroscopic electrical properties of silicone rubber (SiR) are analyzed based on the experimental comparison and the molecular simulation. The insulation properties of SiR with different side group types (vinyl, phenyl, and trifluoropropyl), as well as binary compound SiR (vinyl/phenyl and vinyl/trifluoropropyl) are compared and studied experimentally. Further, the effect of side groups on the movement of the molecular chain is analyzed by calculating the free volume, the mean square displacement (MSD), and the end distances. Then the mechanism of its influence on the macroscopic properties of SiR was studied. The experimental results indicated that the resistance and breakdown performance of the phenyl SiR surpasses both vinyl SiR and fluorosilicone rubber owing to the conjugated structure of benzene ring, which has a high electron affinity and reduces free charges and carrier migration rate. Besides, when 10wt% phenyl SiR was mixed into vinyl SiR, the resistivity increased by one order of magnitude, and the breakdown field strength increased by about 8%. In the aspect of dielectric properties, the fluorosilicone rubber is more qualified than the vinyl SiR and the phenyl SiR due to the addition of trifluoropropyl as a polar group to the non-polar dielectric SiR to boost its dielectric constant and dielectric loss. The molecular simulation results indicated that the SiR containing phenyl has a tiny free volume and weak molecular chain movement, the fluorosilicone rubber has the strongest molecular chain movement. The work has important guiding significance for improving and modifying SiR in power equipment. [ABSTRACT FROM AUTHOR]

To fully understand the distribution network cable accessories’ moisture fault, the variation in insulation parameters of the cable main insulation of cross-linked polyethylene (XLPE) and the cable accessory reinforced insulation of silicone rubber (SIR) under different moisture conditions are studied experimentally. Furthermore, the effects of typical moisture defect forms and moisture positions on electric field distributions are studied by establishing the interface defect model. The experimental results show that the insulation properties of XLPE after water immersion are more seriously reduced than SIR. The resistivity of XLPE and SIR specimens decreases significantly with the increase in moisture time, decreasing by 90.3% and 48.3% after 720 h, respectively. The relative dielectric constants of the two kinds of specimens increase with different degrees after moisture, increasing by 5.16% and 7.83%, respectively, and the breakdown strength decreases by 18.3% and 13.1% after 720 h, respectively. The simulated results show that the moisture form and position have a great influence on electric field distribution. The electric field distortion caused by water trees’ defect is the most serious, followed by water film defects and water droplet defects. Besides, for different types of moisture defects, the position of the maximum distortion electric field is different. [ABSTRACT FROM AUTHOR]

A method of space charge suppression for high-voltage direct current (HVDC) cable is proposed by the modification of the semiconductive layer. In this work, the magnetic particle of SrFe12O19 is used to modify the semiconductive shielding layer, and the effect of SrFe12O19 orientation on the charge accumulation of the insulation layer has been studied. First, the semiconductive composite with different SrFe12O19 contents is prepared and their physicochemical properties are characterized. Second, the effect of the SrFe12O19 orientation in the semiconductive layer and the doping contents on the charge accumulation in the insulation layer is analyzed by measuring the resistivity and space charge. The experimental results show that a certain amount of SrFe12O19 (≤10 wt%) can effectively reduce the positive temperature coefficient (PTC) effect, and the orientation can more effectively reduce the space charge injection from the metal wire core to the insulation layer, thus inhibiting the charge accumulation in the insulation layer. While when the content of magnetic particles is high, it will promote the second injection of the charges, leading to an increase of the charge accumulation. The work provides a new idea for space charge suppression of HVDC cable insulation layer. [ABSTRACT FROM AUTHOR]

A satellite operates in a harsh environment including high vacuum and radiations. The vacuum-dielectric interface is the most vulnerable area to flashover discharge. Moreover, the presence of electron radiation will further decrease the flashover voltage. However, the influence of electron radiation on surface flashover remains unclear. We have performed a study on vacuum DC surface flashover during electron beam irradiation as a function of electron kinetic energy and incident direction on polyimide representative of spacecraft dielectrics. The electron radiation was accompanied by electron deposition and bombardment effects on the polyimide surface. The surface flashover voltage was experimentally found to significantly depend on the kinetic energy and incident angle of the electron beam. By calculating the trajectories of incident electron beam, we further found that the surface flashover voltages are closely connected to the irradiated area. During low energy electron beam irradiation, kinetic electrons are repelled away from the dielectric surface by the applied electric field, and deposited electrons will be dominant in the flashover process, promoting the surface flashover voltage. However, when the electron beam energy is high, kinetic electrons can overcome the applied electric field and strike the dielectric surface to generate secondary electrons, which will replace the field-emission electrons to serve as seed electrons, and initiate the flashover at a much lower applied voltage. These observations and analyses are expected to benefit the research into mitigating spacecraft discharge, and promote the knowledge of surface flashover. [ABSTRACT FROM PUBLISHER]

Charge transport behaviors of dielectric under electron radiation have an important influence on surface flashover performance. In this paper, charging process and model of dielectric during electron radiation are investigated based on the synergistic effect of electron movement on dielectric surface and charge transport properties in dielectric surface layer. For one thing, electrons accumulated in dielectric surface layer will form a reverse electric field acting against kinetic electrons flowing to dielectric surface, which affects the energy and density of electrons reaching the surface. For another, the changes of electron energy and density will further affect the dynamic processes of electron deposition, transport and accumulation in the surface layer. A dielectric charging model is proposed, and charge transport characteristics in dielectric surface and surface layer are obtained, including the temporal behavior of the incident kinetic electrons flowing to dielectric surface, the temporal behavior of secondary electrons and surface conduction charge, as well as the spatial and temporal behavior of the interior potential and electric field. Based on surface potential decay curves of polyimide under different electron energy levels (3-11 keV), the surface potential decay process and model are investigated. The surface trap distribution of polyimide shows different properties under different energy levels. The shallow trap level increases slightly with the increase of electron energy, ranging from 0.81 eV-0.85 eV, while the deep trap level remains unchanged about 0.94 eV. Besides, the amount of trap charge density gradually increases with the increase of electron energy. [ABSTRACT FROM AUTHOR]

The vacuum surface flashover voltage of dielectric material irradiated by electron-beam is very low, which is the key scientific issue for developing high-voltage and high-power spacecraft technology. This paper proposes a novel research way of considering the combined impact of incident kinetic electrons flowing to dielectric surface and deposited electrons in dielectric surface layer on dc surface flashover performance in vacuum. The experiments on dc surface flashover of polyimide in vacuum after electron irradiation and during electron irradiation were investigated. The experimental results indicated flashover voltage showed a distinctly different variation tendency under the two cases. The dc surface flashover voltage of polyimide after electron irradiation became higher than that without electron irradiation, because of the effect of deposited electrons in dielectric surface layer. During electron irradiation, the dc surface flashover voltage exhibited a dramatic drop from 26.9 kV (energy: 5 keV) to 10.5 kV (energy: 30 keV). Furthermore, the surface flashover characteristics exerts different changes for incident electrons of different energies levels. It has been experimentally indicated that the energy and incident trajectory of incident kinetic electrons flowing to polyimide surface are altered by the combined action of the reverse electric field created by deposited electrons and the applied electric field. As a result, the surface flashover characteristics were changed. This work provides a new insight into the vacuum surface flashover of dielectric material under electron irradiation, and can be used as the research basis of surface flashover mitigation methods in space environment. [ABSTRACT FROM PUBLISHER]

Deep dielectric charging in ring structure irradiated by energetic electrons is one of the major factors causing spacecraft anomalies. In this paper, based on the physical processes of charge deposition, transport and accumulation, we establish a 2-D deep dielectric charging physical model of a ring structure consisting of insulating materials, electrodes and aluminum shield. Deep dielectric charging properties of insulating materials irradiated by electron energy spectra are simulated and analyzed under typical space environment and extreme space environment. Furthermore, the influences of aluminum shield, insulating material properties and thickness on deep dielectric charging are investigated. When the thickness of aluminum shield is larger than 3 mm, the maximum electron-beam density reduces to 10-10 A/m2, which is so low that it can not induce high electric field within materials. Selected polyimide (PI), polytetrafluoroethylene (PTFE) and composite epoxy resin (FR4) as electrical insulating materials, space charge transport, accumulation and electric field in insulating material of the ring structure are analyzed. It is indicated that the maximum electric field obeys the sequence as follows: PTFE> FR4> PI. Finally, it is found that the electric field is obviously enhanced with the increasing thickness of insulating material. This work paves the way towards the mitigation of deep dielectric charging. [ABSTRACT FROM PUBLISHER]