No, the insulation in a solid dielectric transmission lines is cross-linked polyethylene, or paper in fluid-cooled lines. Lines are designed to operate well wi

No, the insulation in a solid dielectric transmission lines is cross-linked polyethylene, or paper in fluid-cooled lines. Lines are designed to operate well within the thermal capabilities of the insulation, and there is no such thing as routine replacement of undamaged underground lines. Above-ground transmission lines are uninsulated because they don't need to be, and the extra weight of the insulation would require more expensive towers.