A scientific wild a$$ guess (SWAG) based on television news footage, those cables look to be 2 1/2 to 3 inches diameter (outer jacket size). Cable suitable for underground 27KV usually is constructed with the main high voltage conductor in the center, then the insulation, and then there is a metallic jacket that is grounded, and then some more insulation. Like coax cable. The purpose of the outer metallic jacket is to maintain a uniform electrostatic field thru the inner insulation. To avoid sharp points of electrostatic field that could lead to corona breakdown.
