In this High Voltage AC transmission line wire, the wire has to be composed of bundles of conductors to increase the total surface area of the wire to increase its ampere (capacity) rating and decrease the resistance. In the Direct Current system, the current (electricity) flows along the cross section of the conductor. Where as, in Alternating Current (AC), the current, actually, flows in the surface of the conductor; this is called the “skin effect”. That is why, increasing the conductor surface area by making bundles increases its ampere (capacity) rating and decreases the resistance. Read more about AC and DC transmission systems.