What's the purpose of using three phase AC instead of single phase AC?

Answer 1

The motors are much less complicated, the starters and other control equipment is simpler, a three phase motor uses about 1/3 the electricity used by a single phase motor the same size (if memory serves), there are no "assists" required for starting three phase motors such as capacitors, reversing the motor is much simpler for three phase, and there are "soft-start" electronics for three phase motors.

Answer 2

The power usage is not really an issue. Three phase units are used in commercial buildings because that is what is normally available. Also, three phase splits the amperage into three conductors, you can use smaller wire per conductor and that can be helpful on long wire pulls. Three phase motors have lower amp draw, but they are pulling amps from all three conductors, therefore the overall wattage used does not change much, nor does the electricity cost. Really large units are only produced in three phase, single phase units that size would be impractical.

Answer 3

It is cheaper to run a 3 hp motor on three pahse than a single phase motor.

Answer 4

Three-phase motors are easier to build, since no commutators are needed. Motors require a rotating magnetic field, usually generated by the stator windings. Three-phase power, it is easy to make a rotating magnetic field with those windings. Three-phase motors are either induction motors or synchronous motors.

Answer 5

Single phase simply means there is one sign wave per cycle - one point of peak negative and one point of peak positive voltage.

With three phase, there are three positive and three negative voltage peaks in each cycle. This is a much more powerful and efficient power source - especially for high current devices like industrial motors.

Answer 6

It is cheaper to run a motor on three phase. because it pulls less amps than single.