- [Jon] Hi, Jon here.
In this video, I'm going to show you
how we can generate electricity
using an AC generator.
I'm gonna break it down
as much as possible back
to basic principles so
you can easily understand
how power stations work,
such as hydroelectric power stations,
coal-fired power stations,
nuclear power stations
and you'll also be able to understand
how things like wind turbines work.
How am I gonna do this?
I'm gonna do it by starting with a magnet.
Here's our magnet.
It's got a north pole and a south pole.
The S indicates south and
the N indicates north.
Surrounding the magnet
is a magnetic field.
If I turn on the magnetic field,
we can see that the
north end of the magnet
would attract the south
end of another magnet.
You can see that 'cause
these compass lines
around the side indicate
the magnetic field.
So north attracts south,
and south attracts north.
North would actually repel north
and south would repel south.
But what's interesting about magnets
is that if we move them around,
something really interesting happens.
Now I'm moving this one around,
and it's not really
very interesting at all.
I'll add the field lines,
I'll move 'em again.
You can actually see that
the compass indicators
in the background change
because the magnetic field
surrounding the magnet is
moving with the magnet.
So this is quite interesting.
Now let's go to our next simulation
and I'll show you exactly why.
Here we've got an incredibly interesting
permanent magnet again.
Now moving my magnet around,
you can see over here,
and I'll drag it up to here,
and you can see there's not
really so much happening.
But look what happens when
I move the magnet over here.
And I'll move it back again.
You can see that this light
bulb is beginning to flash.
Now this item here is called a coil
and it's made up of
something called a conductor.
Think of a conductor as being anything
that conducts electricity.
Copper and aluminum are
very good conductors
and that's why we have copper wires
and copper cabling in our households.
The blue dots on this particular conductor
indicate electrons.
As you notice here, if we move the magnet,
we push it through, the
electrons are moving slightly.
We've taken the conductor
and we've wrapped it
in the shape of a coil
because it's a lot easier for us then
to see the effect the magnet
is having on the conductor.
So what can we deduce here?
We know that moving the
magnet through the coil
is somehow generating electricity
because the light bulb
is flickering on and off.
If I move it back and forth like this,
I can actually get it to flicker on
and off quite consistently.
If I do a big move, it lights up a lot.
If I do a slow, little move,
it only lights up a little bit.
That's telling me that if
I change the magnetic field
very quickly, if I pass
that magnetic field
over the conductor,
I'm going to actually make
the light bulb light up
even more than if I do it very slowly.
So what's happening here?
Well, when we move the
magnet through the coil,
we're actually inducing
a voltage in the coil.
In addition to this, we're
actually inducing current flow
because this is a closed circuit.
We know that if I change the
magnetic field very quickly,
then I can induce more voltage
than if I move the magnet very slowly.
What's also interesting is, if
I change the number of loops
on the coil, when I move the magnet,
I actually induce less voltage.
That's telling me that
if I have more conductor
coming into contact
with the magnetic field,
I'm actually going to induce more voltage
than if I have less conductor.
So the area that's coming into contact
with the magnetic field from the conductor
is influencing just how
much voltage I can induce.
So if I add some more loops onto my coil,
it's a lot easier for me
to induce more voltage.
In addition to that, I'm just
going to actually turn down
the strength of the magnet.
We'll notice here that
the strength is zero
and we're not inducing any
voltage in this coil whatsoever,
so there's no current flow either.
When you have a closed circuit,
it's possible to induce a
voltage and induce current flow.
The equation for electrical
power is voltage times current,
so you need both voltage and current
in order to produce electrical power.
Let me turn the strength of
the magnet back up again.
This time, I'm gonna turn it up to 50%.
You can see now we're inducing
a reasonable amount of voltage.
I'll turn it all the way back up to 100%
and it's a lot easier to induce
a lot of voltage and current flow.
Now I don't wanna sit here all
day just going left and right
and inducing current flow in this coil.
At some point, it's
gonna get quite boring.
But notice that every
time I go right to left
or left to right, the light
bulb is actually flickering.
In electrical engineering terms,
we're gonna call this the frequency.
It's the number of cycles we make
with our magnet per second.
Frequency's measured in hertz
and electricity is usually
generated at 50 or 60 hertz,
depending upon where you live.
It's not really possible to move a magnet
back and forth all day
and power entire cities.
We need to find another way of generating
a lot of electricity very efficiently.
I came up with an ingenious solution.
I took my permanent magnet, I
strapped it to a water wheel
and I put a tap above it.
I can turn the water on and
turn the water off again.
I put a conductor coil nearby.
Hopefully, if I turn the water on,
and I play the animation
we can see that the water is running,
the water wheel is rotating,
the magnet is rotating.
Because the magnet is placed
near our conductor coil,
we're inducing a voltage
in that conductor coil.
We've actually got a closed circuit
so there's some current flow as well.
Notice that if we stop the animation,
and I'll just turn off
my water supply as well,
then you can see that
the magnet is stationary
and there is no induced
voltage on our conductor coil.
Stationary magnetic fields
or static magnetic
fields will not allow us
to induce voltage in a conductor.
The magnetic field has to be changing.
This is the reason why you
can't just place a magnet
on a copper wire and generate electricity.
We've gotta keep that magnetic
field constantly changing
in order that we can induce
voltage in a conductor.
What I've effectively simulated here
is a hydroelectric power plant.
If we turn the water on
again, the water wheel turns,
the magnet rotates, the
magnetic field changes
and we can actually see that here.
As the magnetic field changes,
we induce voltage in our conductor coil.
Notice that as N approaches the coil,
we produce a positive voltage,
and S is a negative voltage.
Let me just turn off the
water supply once again.
If we want to induce less voltage,
then there are a couple
of ways we can do this.
One is to reduce the number of coils.
You can see now that
we've induced less voltage
but we're still getting some current flow.
Let's add our loops back on again.
We can turn on the water.
If we actually increase the rate of water,
then our water wheel turns a lot faster,
the magnetic field
changes a lot more quickly
and we induce more voltage.
Not only that, but the frequency increases
as we increase the water flow.
As I mentioned previously,
frequency is measured in hertz,
50 to 60 hertz is pretty standard,
which means we're having 50 to 60 peaks
and troughs every second.
These peaks and troughs are
indicated by this sine wave.
Now, believe it or not,
you've actually just learned
how we generate enough electricity
to feed entire cities and
continents with power.
Essentially, all we need is some way
to create a varying magnetic field
and to pass that magnetic
field over a conductor.
If we can do that on a very large scale,
then we're going to be able
to generate electricity.
In our example, we took a
magnet and we strapped it
to a water wheel and we
induced the voltage in a coil,
which allowed us to induce current flow,
and we know that power
equals voltage times current,
so we are generating electrical power.
I have to stress here though
that we say generating,
but we're not actually generating anything
because you can't generate energy.
You can only transfer energy
from one form to another.
In our example, we're using
the kinetic energy of the water
as it impacts our water
wheel to rotate the magnet
and that allows us to induce voltage
and ultimately generate electricity.
We're transferring the kinetic
energy to electrical energy.
There are three types
of common hydro turbine.
These are the Kaplan,
Francis and Pelton turbines,
but all of those hydro turbines
and pretty much every
hydroelectric power plant
on the planet is using the basic concept
that we've just learned about,
rotating a magnet to
change a magnetic field
to induce a voltage.
If we look at a Kaplan runner,
we simply allow water to
flow over the turbine runner.
The runner looks a lot like a propeller.
The propeller turns.
We attach the propeller to a shaft,
then we attach the shaft to a generator,
specifically, the shaft from our turbine
connects to our magnet.
Inside a generator,
our particular magnet is called
a rotor because it rotates.
The turbine runner propellor turns,
the shaft turns, the magnet turns,
and surrounding the magnet
we have our conductor coil.
The conductor coil is stationary
and we refer to it as a stator.
Once the water is flowing,
the propellor is turning,
the shaft is turning, and our
generator rotor is turning,
we are then inducing a
voltage in our stator
and thus generating electrical power.
Wind turbines, exactly the same concept.
We allow wind to flow
over our turbine blades.
The blades begin to rotate.
We connect our blades on a common shaft
to our generator rotor.
The rotor begins to rotate.
We induce voltage in a stator
which surrounds the rotor
and again we have electrical power.
When we start looking at
coal-fired power stations,
it gets slightly different
because we're not gonna convert
the kinetic energy from water
or from the air into electrical power.
We're actually gonna convert the energy
from coal into electricity.
So how do we do that?
Well, fuels are essentially hydrocarbons.
We want to burn the hydrogen
contained by the fuel
in order to release its energy
and we'll transfer that energy,
using a boiler, to some water.
We'll boil the water,
we'll turn it to steam.
We'll pass that steam
over a steam turbine.
The steam turbine will begin to rotate.
We'll connect that then
to our generator rotor.
The rotor begins to rotate
and we induce voltage
in a stator, and again, we
generate electrical power.
How much power can we generate?
Well, it depends.
If we burn a lot of coal,
then we can release a
lot of thermal energy.
We transfer that to the
steam and ultimately
we then transfer it to
our electrical system.
So irrespective of if we're
generating electricity
using hydro turbines or wind turbines
or coal-fired power stations,
we can only ever get
as much energy out as we put in.
In fact, typically we
get far less energy out
than what we put in because of losses.
Although we strapped our
magnet to a water wheel,
I have to stress that
are many other options
available to us.
We're just looking for something
that will make our magnet
spin continuously in a circle.
We want something that will
make our magnet rotate.
Strapping it to a water wheel
and having some water flow
across the wheel is a good way
to keep our magnet running continuously.
But we can also strap our
magnet to a wind turbine rotor
and it will also spin continuously.
Or perhaps we can strap it somehow
to the shaft coming
out of a steam turbine.
That will also work.
Or we'll take a diesel engine
and connect it to a shaft
on the diesel engine.
All of these items that rotate our magnet
are referred to as prime movers.
They're the items that allow us
to transfer mechanical
motion or mechanical energy
to our magnet in order that
it rotates so that ultimately
we transfer our mechanical
power to electrical power.
You now know how we generate electricity.
But you should also understand
that the basic principles
that you've learned in
this video can be applied
to hydroelectric power stations,
nuclear power stations,
coal-fired power stations,
in order to understand
exactly how they work.
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