The invention discloses a composite medium for a cable insulating material and a preparation method of the composite medium. The composite medium comprises a gradient layer, an interface
passivation layer and a substrate layer which are sequentially connected from top to bottom, the gradient layer is a gradient layer, the interface
passivation layer is an aluminum
oxide layer, and the substrate layer is a high
dielectric constant
ceramic layer. Through the composite medium composed of the substrate layer, the interface
passivation layer and the gradient layer, the problems of high
dielectric constant
temperature sensitivity, leakage conductance caused by interface defects and insufficient breakdown
field strength of the composite medium are effectively solved, the condition of
insulation failure of a cable insulation material is avoided, the substrate layer provides
thermal stability support for the composite medium, and the service life of the cable is prolonged. The interface passivation layer blocks
oxygen vacancy migration, so that the leakage current of the composite medium is reduced, the gradient layer reduces the
dielectric constant wide-temperature fluctuation rate of the composite medium, the breakdown
field strength is improved, and the condition of
insulation failure of a cable insulation material is avoided.