8.9 : 三相电路和单相电路中的功率分配

Consider a two-wire single-phase system providing electricity to homes and a three-wire balanced three-phase system powering a factory with heavy machinery.

Both systems use wires of the same material and length with resistive loads and have the same line voltage and absorbed power.

In the single-phase system, the current equals the ratio of the absorbed power to the line voltage, with the power loss proportional to the square of the absorbed power divided by the square of the line voltage.

For the three-phase system, the current is divided into three wires, and the total power loss is calculated differently.

In the ratio of the power losses of the two systems, resistances are substituted in terms of the wire radii.

If power loss is equal in both systems, the wire's radius in the single-phase system is twice that of the three-phase system.

Comparing the material required for the two systems, the single-phase system uses 33% more material than the three-phase system.

So, for the same power output, a three-phase system substantially minimizes material consumption, enhancing its power distribution efficiency.