What characteristic of three-phase systems makes them efficient for power transmission?

The characteristic that makes three-phase systems efficient for power transmission is that they allow for a lower current at a given power level. In a three-phase system, power is transmitted more effectively because it distributes the electrical load evenly across three conductors. This reduces the current needed in each phase for a given amount of power, compared to single-phase systems, which in turn decreases resistive losses in the transmission lines according to the formula P=I²R, where P is the power, I is the current, and R is the resistance.

Lowering the current is vital because resistive losses increase with higher current. Therefore, in three-phase systems, the same power can be delivered at a much lower current level than in single-phase systems, leading to higher efficiency and reduced heating in transmission lines.

While higher voltage, fewer wires, and the ability to operate at lower frequencies contribute to specific advantages in certain cases, they do not directly relate to the efficiency of power transmission in the same way that lower current does.