1. Transformer Basics
1.1 Basic Transformer Theory
Figure 1 represents the essential elements for a transformer - a magnetic
core, with a primary and secondary coil wound on the limbs of the magnetic
core.
Figure 1. A Basic Transformer
An alternating voltage (Vp) applied to the PRIMARY creates an
alternating current (Ip) through the primary.
This current produces an alternating magnetic flux in the magnetic core.
This alternating magnetic flux induces a voltage in each turn of the
primary and in each turn of the SECONDARY.
As the flux is a constant e.g. the same in both primary and secondary: -
Vp = const Np
Vs = const Ns
This equation shows that a transformer can be used to step up or step
down an ac voltage by controlling the ratio of primary to secondary turns.
(Voltage transformer action).
It can also be shown that: -
Primary VoltAmperes = Secondary VoltAmperes
VpIp = VsIs
This equation shows that a transformer can be used to step up or step
down an ac current by controlling the ratio of primary to secondary turns.
(Current transformer action)
It will be noted that there is no electrical connection between the
primary and secondary windings.
A transformer therefore provides a means of isolating one electrical
circuit from another.
These features - voltage/current transformation and isolation, cannot be
obtained efficiently by any other means, with the result that transformers
are used in almost every piece of electrical and electronic equipment in
the world.