They are used to
change voltage by
stepping up theprimary voltage on the
stepping down the voltage. They are also used to match impedance and as
isolating devices that isolate the ground.
A.C. is required to operate transformers because the
that occurs between the primary and secondary requires a rapidly
and collapsing electromagnetic field that only alternating current provides.
Because electrical power distributed as
high voltage has a reduced
current, smaller cable sizes can be used.
The cost effectiveness of
smaller cables is the reason for high voltage distribution but it must
be stepped back down for consumer safety.