Functionally Graded Insulator with Periodical Lattice Structures Enabling High Insulation and Mechanical Strength

Functionally graded insulation (FGI), which has a spatially non-uniform distribution of permittivity and/or conductivity, has been verified to be advantageous in better electric field distribution and enhanced insulation strength. To address the challenge of practical application of FGI (including the uncertainties of permittivity/conductivity distribution and difficulties in grading structure fabrication), periodical lattice material (PLM) can be employed due to its accuracy in properties and simplicity in fabrication. In this paper, the lattice-type composites with three-dimensional periodic truss structure were used for the construction of FGI, and the gradient distribution of relative permittivity was realized through structural adjustments of lattice unit cells. Based on previous research, this paper specifically focused on exploring the improvement of surface electrical strength and mechanical strength. Using the combined process of 3D printing and vacuum casting, lattice graded insulators and ISO-standard mechanical testing bars were prepared. The results of flashover voltage (FOV) test demonstrate that, compared with the original insulator, the lattice graded insulator achieves a surface FOV improvement of $14.6 \%, 57.8 \%$, and 48.3% in 0.1 MPa air, C4F7N/CO2, and SF6, respectively. Moreover, three-point bending strength of lattice structure is higher than both the truss lattice and filling material, demonstrating the enhancement of mechanical strength by the optimization of internal structures. This research indicates that PLM based functionally graded structure can be advantageous in both electrical and mechanical properties, providing a novel and practical solution for industrial employment of FGI components.