The invention discloses a preparation method of a high-
voltage and ultrahigh-
voltage cable insulating material. The preparation method comprises the following steps: (1) compressing an
ethylene monomer, carrying out high-pressure
polymerization in a reactor to obtain low-density
polyethylene, separating by a high-pressure separator and a low-pressure separator, cooling the low-density
polyethylene, directly feeding into a single-screw extruder, adding a liquid
antioxidant, uniformly dispersing the liquid
antioxidant into low-density
polyethylene, filtering through a high-mesh filter screen, and granulating to obtain low-density polyethylene containing the
antioxidant; and (2) dedusting and grading the antioxidant-containing low-density polyethylene, adding a cross-linking agent by adoptinga post-
permeation method, fully stirring, putting into an absorption bin, keeping the temperature, cooling, dedusting, removing impurities, and carrying out
metal filtration to obtain the high-
voltage and ultrahigh-voltage cable insulating material. According to the method provided by the invention, secondary melting
processing of low-density polyethylene is avoided,
thermal aging of resin is reduced, the cleanliness and the stability of the insulating material are improved, and the method is high in production efficiency, low in cost and convenient to popularize and apply.