- [Instructor] Hi, John here. In this video, we're going to have a look at how power grids work. We'll look at all of the main components that make up a power grid, and I'll explain to you
how they work together in order that we can get electricity from a power station to your home. By the end of the video, you'll
know how power grids work, what all the main components are, what their purpose and
function is within the grid, and if you're ever out and
about in the real world, you'll be able to walk passed things like electrical
transformers, or substations, or transmission towers, and you'll be able to
identify them visually and know why they're there
and what their purpose is. So let's start by looking at a basic diagram of a power grid. You can see here on our power grid that we've got five letters, and these five letters are A, B, C, D, E, and they indicate different
parts of our power grid. If we look at letter A, it marks the generation
part of the power grid. If we look at letter B, this represents the transmission
part of the power grid. Letter C is the distribution part, and letters D and E
represent our end consumers. Generally, when we're
talking about power grids, we split it into three main sections, generation, transmission,
and distribution. If you wanna talk about letters D and E, then we'll simply refer
to them as the consumers. I suppose you could call it the consumption part of the power grid. You can see on the diagram that we've actually got some transformers and substations between the letters, we've got a power transformer, transmission substation and
distribution substation. Don't worry about those too much now. I'm gonna explain to you what
transformers are used for and why we have substations, et cetera a little bit later in the video. So let's go to letter A first, generation. Now don't be fooled by the name. We refer to it as power generation in the power generation industry, but we're not actually
generating any power. The power that we're referring
to is electrical power, and it's not possible to
create or destroy energy, and therefore it's not possible to create or destroy
electrical power either. If you wanna get technical, this is actually called the
first law of thermodynamics, also known as the law of
conservation of energy, and it simply means that
we can transfer energy from one form to another, but we cannot create or destroy it. So in order to get the energy that we're gonna put into our power grid, we're going to need to
find another energy source and then convert that energy
source into electrical power. Now there are various ways of doing this. If we're burning coal, then
we burn coal within a furnace, we release the chemical
energy that the fuel contains, we turn it into heat, we
transfer that heat to water, the water gets heated
up and turns to steam, we put the steam through a steam turbine, the turbine rotates, and we transfer the mechanical motion, that is the mechanical energy, can also say mechanical power, to a generator. Now this generator is
actually what they refer to as a synchronous three phase generator, at least 95% of the times
in the power industry that's what it will be, and the generator converts
the mechanical power that it's getting from the steam turbine into electrical power. So we started with chemical energy that's contained within a fuel, and we burned it and we
turned it into, in the end, electrical power. If we're looking at a
hydroelectric power station, we'll take the pressure
energy, or potential energy, we'll take the kinetic energy, and we'll harness this by letting it flow across
a hydro turbine runner, the runner rotates, and then we pass this mechanical motion or mechanical power onto our generator, and the generator turns
that mechanical power into electrical power. So there are a number of different ways in order that we can harness
different energy sources in order to get our electrical power. Those are just two common ones. A wind turbine is much the same. We're just taking rotary motion and using that to rotate
a rotor in a generator. So now that we've generated
our electrical power, I say generated, but I suppose we really
should say converted. Either way, we've got our
generated electrical power, and now we're gonna need
to feed it into the grid so that we can send it to our consumers. Now it's at this point that we
encounter our first problem. Most power stations are very
far away from end consumers. If we were to lay a cable
or a electrical conductor from our power station
to our end consumers, and let's just imagine for a moment that our end consumer
is 20 kilometers away, well we're going to encounter losses due to the resistance of
our electrical conductor and also due to the heat that's generated as electricity or electrical
current, that is amps, flows through our conductor. This wouldn't be such a big problem if we could have a very large conductor, but unfortunately, having
a very large conductor that stretches across
20 kilometers of land is not very practical. So we need to go back
and have a look at why we've got such large losses whenever we dispatch
power over a distance. Well the equation for electrical power is voltage times current, and the equation for
power loss is I squared R. The I indicates current, and
the R indicates resistance. We can vary the resistance in our cables by having good electrical conductors, and these include materials
like copper and aluminum which have high conductivity. But these materials cost a lot of money, and considering we're
potentially going to need thousands of kilometers or
thousands of miles of conductor, we want to make these
conductors as thin as possible, so they need to have
quite a small diameter. The problem here is, as we reduce the diameter of a conductor, its ability to carry current reduces also. When current flows, it generates heat. If we have a very thin conductor
and a very high current, the current will simply
melt the conductor. So how do we reduce the current? Well we can reduce the current
by increasing the voltage. Power equals voltage times current, or P equals V multiplied by I. So if we increase V by a factor of 10, then I has to reduce by a factor of 10. That has to occur because if we want to balance
both sides of the equation, the power out has to
remain always the same. That means if we increase the voltage, we have to proportionately
decrease the current. So we need to increase the
voltage, that much we know. And if we can do that, we'll
reduce the amount of heat that's generated as current
flows through our conductor. That means we can have thinner or smaller diameter conductors, which is ultimately
gonna save us some money. But the other large benefit here is that power losses are represented by P equals current
squared, multiplied by R. So power loss equals current squared, multiplied by resistance. So the big number here is current. On this example here, you can see that if we double the current and make no other changes to the equation, we quadruple our power losses. That doesn't happen if we
double our resistance value. So our priority, if we
wanna reduce power losses, is to reduce the value of current, and we can do this by
increasing the voltage. So to recap, in order to
have smaller conductors, which ultimately saves us money because they can be much thinner or have smaller diameters
than larger conductors, and in order to reduce our power losses mostly due to the generation of heat, we need to reduce our current
level as much as possible. How are we going to do that? This is why we have
electrical transformers. People underestimate just how important electrical transformers
are to our daily lives. You may think that they're
not that important, and perhaps you may think you haven't seen many
of them around before, but if you live in a city or town, I can guarantee that
there'll be a transformer within about 400 meters radius of where you're sitting right now. You might not notice them because sometimes they're
hidden inside houses, or small buildings, or sometimes they've just
got a wall around them so no one can see them, but they are a hundred percent there. They're essential to the
way we live our daily lives. Let's now discover exactly why. We need to increase the voltage. We know that much because we
need to reduce the current. Transformers work on the principle of electromagnetic induction, and this states that every conductor that has current flowing through it creates a magnetic field. If we take a conductor and we wrap it into the shape of a coil, and then we take another
conductor and place it nearby, we can actually transfer current from one conductor to the other without them ever physically coming into contact with each other. Electricity and magnetism are linked. That means if one of the conductors is connected to a power source and electrical current is flowing, the magnetic field that
surrounds that coil is going to have an impact
on the other coil nearby. What's really interesting though is this only works with
alternating current. The magnetic field has
to be constantly changing in order that we can induce
voltage in our other coil. The coil that's connected
to the main power supply is referred to as our primary coil. The alternating current that
is flowing through that coil creates a magnetic field
that expands and contracts as the current flows back
and forth through the coil. This induces voltage
in our secondary coil. In this way, we can transfer current from our primary coil
to our secondary coil without them ever coming
into contact with each other. As current flows back and
forth on our primary coil, the magnetic field
increases and decreases, and that causes current
to flow back and forth in our secondary coil. In electrical transformers,
we actually mount these coils onto a big block of steel. The big block is called
the transformer core, and although it looks like
a solid piece of metal, it's actually made up of a
lot of thin, laminate sheets which are either glued
or clamped together. The reason we have the core is just to focus the magnetic field from the primary winding
to the secondary winding. The core makes the transformer
a lot more efficient. What's really fascinating
is if we add more windings to the secondary side of our transformer, we can increase the voltage. If we reduce the number
of secondary windings on our transformer, we reduce the voltage. Remember, we want to increase the voltage in order that we can reduce the current and reduce our power losses. So transformers that are installed directly after power stations have many, many more secondary windings than primary windings. This allows us to increase the voltage. Transformers that increase voltage are referred to as step-up transformers, and transformers that reduce voltage are referred to as step-down transformers. The transformer directly
after a power station is called a generator step-up
transformer, or GSU for short. Once we have increased the voltage, we're gonna send our electrical
power to a substation. This is usually some type
of open air switch yard. And then we're gonna feed that power into our transmission lines. And these lines are held
by our transmission towers. Transmission towers have
a very unique shape. They're often very tall, and there's a good reason for this. The electrical conductors that are used on our transmission
lines are not insulated. In your home, when you have
an electrical conductor like a copper cable for example, you're going to have a
sheet of plastic or rubber around that cable, and that is what insulates the cable and stops the electrical current from shorting out by going to ground. So insulate the conductor in our homes in order that current
flows where we want it to and that we don't have short circuits. The conductors that we use
on our transmission lines do not have any plastic or
rubber surrounding them, but they are, however, insulated. You just can't see the insulation. They're what we refer to as air insulated. And the reason we have
to hang these conductors on a large tower is because air is not
such a fantastic insulator that we can leave the conductors hanging around one meter above the ground. If we did this, the air
surrounding the conductor would be ionized to such a degree that we would get an electrical arc from the conductor to ground. This arc would look like a large spark. So we hang our conductors
high above the ground so that there is a large air gap between the conductors and ground. This gives us a large
amount of air insulation. Not only that, but it keeps
the transmission lines well out of the way of the general public because we don't want people driving into our transmission lines or accidentally flying a kite into them and causing a ground fault. It's not good for the power grid, and it's definitely not good for the person holding the kite. Although we've insulated
our transmission lines from the ground, we also need to insulate
them from the tower itself, which would act as a
very efficient conductor if our transmission lines came near or touched onto the tower itself. To ensure this doesn't happen, we hang our transmission
lines from the tower using insulators. Insulators allow us to bring the transmission
lines to the tower without bringing them
too close to the tower. Initially, when we
generated electrical power using our generator, we may have had a voltage of 20,000 volts. When we reach the transmission stage, we may have a voltage
of 130, 230, 340, 500, or even 765,000 volts. That is a lot of volts, especially when you consider in your home you may use 220 volts or 110 volts. So we've massively increased the voltage in order to reduce our transmission losses and in order to be able to reduce the size of our conductors. We're now distributing our power across potentially hundreds
of kilometers or miles before we reach the next
part of the power grid. Once again, we reach a substation. Substations contain all
of the equipment we need in order to reduce and increase voltage. Not only that, but they
allow us to separate various parts of the grid from each other. This means we can protect different parts of the
grid from each other so that if we have things
like lightening strikes or power surges, we can isolate certain areas of the grid rather than have a complete blackout. Substations are critical
if we want to ensure that the machinery and the components that make up the power grid are as protected as much as possible so that we can increase the
reliability of the grid. Substations contain items
such as surge arresters or lightening arresters, circuit breakers, switchgear, disconnectors, and transformers. We've left the transmission stage, and now we're gonna go to
the distribution stage. We don't want to send electrical
power to our end consumers at 765,000 volts. They're not gonna like
that very much at all. So we'll reduce the voltage
using a step-down transformer. And remember, this is a transformer that has far fewer windings
on the secondary side than it does on the primary side. Different consumers
require different voltages. Industrial plants, for example, may require voltage to be delivered at 30,000, 20,000, or 10,000 volts depending upon the
application of the plant. Large office buildings and hospitals will require lower voltages. And by the time we reach
the general consumer living at home, they're gonna require voltages
of 380 volts to 40 volts, or even 110 or 120 volts. Because there are multiple consumers requiring multiple voltage levels, we're going to need multiple transformers, and each specific transformer is going to cater for one
specific voltage level. Now that we've reduced the
voltage to quite low levels, it's essential that we
deliver that electrical power over as short a distance as possible. And this is the reason why, if you're living in a city or town, a transformer will be located nearby. So you now know how we
get electrical power from our power generation source, which may be a coal-fired power station, perhaps a series of wind turbines or a hydroelectric power plant, et cetera, and how we transfer that
electrical power to our homes even though our homes
may be miles and miles or kilometers and kilometers
away from the power source. If you wanna learn more about engineering, then be sure to check out our website. We've got over 25 hours of
engineering video tutorials, and we cover everything
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