Download How do they work?

What do they do?
Fundamentally a transformer is able to step the voltage
up or down from the powered coil to the unpowered coil,
ie change the voltage coming out of the transformer!
How do they work?
There is an effect of electromagnetism
known as mutual induction.
Two or more coils of wire placed so that the changing
magnetic field created by one induces a voltage in the
other.
If we have two inductive coils and we energise one coil
with AC, we will create an AC voltage in the other coil.
When used as such, this device is known as a
transformer:
Why should AC be used rather than DC?
As useful as transformers are, they only work with AC.
Since the phenomenon of mutual induction relies on
changing magnetic fields, and direct current (DC) can
only produce steady magnetic fields, transformers
simply will not work with direct current.
Of course, direct current may be interrupted (pulsed)
through the primary winding of a transformer to
create a changing magnetic field (as is done in
automotive ignition systems to produce high-voltage
spark plug power from a low-voltage DC battery), but
pulsed DC is not that different from AC.
Perhaps more than any other reason, this is why AC
finds such widespread application in power systems.
Why have an Iron core?
The laminated iron core simply
redirects the magnetic field from
the primary coil through the
secondary.
What is the relationship between the Voltage
produced and the current?
If the secondary coil is powering a load, the
current through the secondary coil is just the
opposite ie If the Voltage increases the
current decreases
Relationship between Voltage and Number
of turns
In any transformer the number of turns has
an effect on the voltages produced.
You will remember making electromagnets in
Key Stage 3 where the number of turns of
wire affected the strength of the magnet.
If more turns were used you made a
stronger magnet. Therefore the amount of
coils of wire around a transformer could
affect the output!?
Output proportional to turns
The strength of the magnetic field is
proportional to the input voltage and the
number of turns around the the primary coil.
Therefore, the output voltage must be
proportional to the strength of the changing
magnetic field and the number of turns on the
secondary coil.
A typical arrangement of a transformer is
shown below.
The relationship between the number of turns
on the primary and secondary is mirrored in the
input and output voltages.
This relationship has
a very close
mechanical analogy,
using torque and
speed to represent
voltage and current,
respectively:
If the winding
ratio is
reversed so
that the
primary coil has
less turns than
the secondary
coil, the
transformer
"steps up" the
voltage from
the source level
to a higher level
at the load:
Relationship between turns and voltages
The Voltages in the primary and secondary coils are
linked in the same way as the number of coils in the
primary and secondary. They have a constant ratio
as shown below……
No. of turns on primary
No. of turns on secondary
= Voltage on primary
Voltage on secondary
Industrial Applications
You need to research the application of transformers
with regard to the large scale transmission of
electricity.
This means you have to explain the use of
Step up and Step down transformers on power
lines.
You need to discuss the effect of these
transformers on the voltages at all stages and the
reasons why in terms of energy loss in the power
lines.
The transformer's ability to step AC voltage up or
down with ease gives AC an advantage unmatched by
DC in the realm of power distribution.
When transmitting electrical power over long
distances, it is far more efficient to do so with
stepped-up voltages and stepped-down currents
causing lower resistive power losses, then step the
voltage back down and the current back up for
industry, business, or consumer use.
Transformer technology has made long-range
electric power distribution practical. Without the
ability to efficiently step voltage up and down, it
would be cost-prohibitive to construct power
systems for anything but close-range (within a
few miles at most) use.