The electric field grading of dielectric permittivity gradient devices is an effective way of enhancing their insulation properties. The in situ electric field‐driven assembly is an advanced method for the fabrication of insulation devices with adaptive permittivity gradients; however, there is no theoretical guidance for design. In this study, an analytical model with a time constant is developed to determine the transient permittivity of uncured composites under an applied AC electric field. This model is based on optical image and dielectric permittivity monitoring, which avoids the direct processing of complex electrodynamics. For a composite with given components, the increased filler content and electric field strength can accelerate the transient process. Compared with the finite element method based on differential equations, this statistical model is simple but efficient, and can be applied to any low‐viscosity uncured composites, which may contain multiple fillers. More importantly, when a voltage is applied to an uncured composite insulating device, the proposed model can be used to analyse the spatiotemporal permittivity characteristics of this device and optimise its permittivity gradient for electric field grading.
Electric-field grading by dielectric permittivity gradient devices is an effective way of enhancing the insulation performance. In situ electric-field-driven assembly is an advanced method for the fabrication of insulating devices with adaptive permittivity gradients; however, there is no theoretical guidance for its use in design. We develop an analytical model for the spatiotemporal permittivity of an uncured-composite device in an AC electric field and investigate the coupling effects between the in situ assisted electric field and rod-like filler self-assembly in three devices: a pin-flat insulator, a basin insulator, and a silicone-gel-insulated gate bipolar transistor. Our model is based on optical images and dielectric permittivity monitoring, thus avoiding complicated electrodynamic calculations. The electric-field uniformity follows a U-shaped curve with assisted-voltage application time. We also find a combination of experimental parameters that constitutes an optimal tradeoff between internal and surface electric-field uniformities. This work establishes a theoretical design framework to optimize the performance (e.g. flashover voltage and breakdown strength) of a composite device.
Dielectric gradient components have advantages in electric field mitigation and insulation improvement. In this paper, we propose a fabrication method for adaptive dielectric gradient components using in situ AC electric field, including the mechanism and the corresponding operational procedures for industrial applications. Based on the electric polarisation and self‐assembly effect of the filler particles in the liquid matrix, the chain‐like structure in the high field strength region is constructed to enhance the local permittivity and mitigate the maximum of the spatial electric field. The dielectric gradient basin insulator is prepared by this method, and its flashover voltage is increased by 12.8% compared with that of a homogeneous dielectric basin insulator, and the improvement is 20.8% when metal particles are present on the surface. The more non‐uniform the initial electric field is, the greater the improvement in flashover voltage. This method is expected to promote the industrial application of dielectric gradient insulating components.
Oxygen vacancy plays an important role in the flash sintering (FS) process. In defect engineering, the methods to create oxygen vacancy defect include doping, heating, and etching, and all of them often have complex process or equipment. In this study we used dielectric barrier discharge (DBD) as a new defect engineering technology to increase oxygen vacancy concentration of green billet with different ceramics (ZnO, TiO2 and 3 mol% yttria-stabilized zirconia (3YSZ)). With a 10 kHz AC power supply, the low-temperature plasma was generated and the specimen could be treated in different atmosphere. The effect of DBD treatment was influenced by atmosphere, treatment time, and voltage amplitude of power supply. After DBD treatment, the oxygen vacancy defect concentration in the ZnO samples increased significantly, and the resistance test showed that the conductivity of the samples increased by 2-3 orders of magnitude. Moreover, the onset electric field of ZnO FS decreased from 5.17 kV/cm to 0.86 kV/cm at room temperature, while in the whole FS the max Power dissipation decrease from 563.17 W to 27.94 W. The defect concentration and conductivity of the green billets for TiO2 and 3YSZ also changed by DBD, and then the FS process was modified. It is a new technology to treat green billet of ceramic in very short time, applicable to other ceramics, and beneficial to regulate the FS process.
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