Download How electricity is made

How electricity is
made
Electricity can be made or generated
by moving a wire (conductor) through
a magnetic field.
Magnetism
►
A bar magnet has a north
and south pole. If it is
placed under a sheet of
paper and iron filings are
sprinkled over the top of
the paper, these iron filings
will arrange themselves
into a pattern of lines that
link the north pole with the
south pole of the magnet.
These lines show the
magnetic field around the
magnet.
Making electricity
►
If a coil of wire is moved within a magnetic field so that it
passes through the magnetic field, electrons in the wire are
made to move. When the coil of wire is connected into an
electric circuit (at the terminals A and a) the electrons get
energy to move in a certain direction and a current will
flow. This electrical energy is called voltage.
Making electricity
►
The amount of energy or voltage depends on the strength
and position of the magnetic field relative to the coil, as
well as the speed at which the coil is turning. As the
amount of electricity changes so does its voltage.
Making electricity
►
In the adjacent diagram,
the coil of wire is rotating
in a clockwise direction.
When the coil of wire is in
the horizontal position the
voltage is greatest
(diagram), because the
coil is passing through the
strongest part of the
magnetic field. At this
stage the current flows
from 1 to 2 to 3 to 4, out
through terminal a,
through the globe and
back into terminal a.
Making electricity
►
When the coil of wire is in
the vertical position, no
electricity is produced
because the coil does not
cut the magnetic field, and
no current flows.
Making electricity
►
When the coil of wire is in
the horizontal position
again, the voltage is at its
maximum (diagram),
however the current flows
in the opposite direction 4
to 3 to 2 to 1, out through
terminal a, through the
globe, and back into
terminal A.
Making electricity
►
The current produced changes direction every half turn
(180 degrees ). This is called alternating current or AC.
The generators at large power stations produce nearly all
the electricity we use in this way.
Power Stations Generators
►
►
With large power station generators, the coils actually
remain stationary, and the magnetic field rotates. This still
produces the same effect as described above. The magnet
rotates as the turbine to which it is attached rotates.
When only one of the coils of wire is connected in the
stationary part of the generator (known as the stator), the
electricity circuit is said to be one phase (or one circuit).
shows what a rectangular coil or winding may look like
Power Stations Generators
►
It is mounted inside the
stator as in the picture and
has terminals A and a.
When the magnet rotates
the voltage is produced as
shown in diagram.
Power Stations Generators
►
►
It is more cost efficient and
technically better to connect
three sets of coils in the
stator.
The picture shows how
these coils are mounted.
Each of these coils will be
connected as separate
electrical circuits. When the
magnet rotates an identical
voltage is produced in each
coil and circuit, but each is
staggered or delayed from
one another (see diagram).
The electricity circuit is said
to be three phase.