Another important advantage of three-phase power is that, as will be explained
in Chapter 17, three-phase motors have a nonzero starting torque, unlike
their single-phase counterpart. The change to three-phase AC power systems from
the early DC system proposed by Edison was therefore due to a number of reasons:
the efficiency resulting from transforming voltages up and down to minimize
transmission losses over long distances; the ability to deliver constant power (an
ability not shared by single- and two-phase AC systems); a more efficient use of
conductors; and the ability to provide starting torque for industrial motors.