What is the prinicple of apower transformer?
An electrical transformer consists of a two sets of
coils, called a primary winding, and a secondary winding. These are
electrically separate from each other, and are coupled together
magnetically via an iron core. (Of rather special design). It is
called a transformer because it transforms one voltage (in a.c.)
into another voltage.
The amount of power able to be transferred between the
coils is governed by the amount of iron in the core. If each
winding had the same number of coils of wire, then the transformer
would produce a voltage at the output equal to that at the input.
This would be called an isolating transformer and are used
for safety reasons.
If the secondary had twice the number of turns as the primary,
then the voltage produced would be twice that of the primary. But
the current would still be limited by the size of the iron core,
and by the size of the wire in the windings. In this example, the
current available would be halved.
It is common for a transformer in an electronic system to have
multiple windings, some low voltage, some medium voltage, and some
high voltage. And they may be used to reduce the voltage as well as
to increase it.