A design choice
When it came to chose the system for the distribution of electrical energy,
following options were open:
1. AC vs DC
The Alternate Current was an easy win for a simple reason:
it allowed the conversion to high voltage and vice versa with a simple static machine:
the transformer. The use of high voltage for transport is convenient because
power losses are inversely proportional to the square of voltage.
2. Number of wires. Following were the options:
One wire, with return on ground
Although possible and actually used also nowaday
for distributing energy in rural areas, has not been adopted for
stability and safety concerns.
it solves the problems of single wire system, but cannot be used to
directly generate a rotating magnetic field, which is desirable to run motors.
It allows the direct creation of rotating field, and so the use of
the simple to build induction motors.
A three-wire system can be implemented with Ferraris idea of having two phase
with one common wire, but this would not lead to a symmetrical system,
therefore it would not be suitable for enery transmission.
Tesla system is superior, as shown below.
This system is not suitable for transmissione of energy, due to the asymmetry of voltages.
Voltages are symmetrical, the system is suitable for energy transmission.
Also, three-phase motors can be directly connected.