The national grid transmits
electrical power at a very high potential difference and a very low current. Why is this?
Okay, so when we talk about the
national grid, we’re speaking of a very large-scale electrical network. This network has three main
sections or parts to it. These parts are generation, where
electricity is generated, transmission, where the electrical energy travels over
large distances, and then distribution, where the electrical energy is delivered to
its end users. Now, our particular question is
asking about the transmission phase of this process.
During this phase, electrical
energy is transmitted over large distances up to hundreds of kilometers. During this process, one of the
most important considerations is the efficiency with which electricity can get from
one point to another. That is, of all the electrical
energy that goes into the transmission wires in our network, we want as much of that
energy as possible to make it out the other end at the distribution phase. In other words, during
transmission, we want to minimize the energy lost.
Now, if we picture a wire in our
transmission network, we know that electrical current travels through that wire. And we also know that the more
current flows in the wire, the more the wire heats up. Now, this heat is not a way that we
want this electrical energy to be used. We prefer the energy make it to the
distribution phase where it can be used in homes and businesses. So during the transmission phase,
we would like our wire heating to be a small as possible. And the way to do that is to make
the current running through these wires as small as possible. So the smaller our current 𝐼 is
that runs through these transmission wires, the less the wires heat up, and
therefore the less energy is lost due to heating.
But interestingly, because of the
properties of electricity, if we want to change the current 𝐼, there’s another
property we’ll need to change, and that’s the potential difference 𝑉. The reason for this comes down to a
mathematical expression for electrical power. This equation tells us that power
is equal to potential difference or voltage multiplied by current 𝐼. The electrical power moving through
the transmission lines of our national grid depends on the power plant that was used
to generate that electricity. For a given power plant, we can
consider the electrical power 𝑃 in the transmission lines to be a constant. In other words, 𝑃 in this equation
is fixed. That’s something that we’re given
rather than something we can change.
This means that if we want to
decrease the current running through our transmission lines and we do because that
will minimize energy losses, then in order to do that, we’ll have to increase the
potential difference of our electricity. It’s only by doing both of these
things that we can decrease the current as well as keep the power constant. And so we now see why the national
grid transmits electrical power both at very high potential difference and at very
low current. We can write out that reason this
way. We can say that while high current
heats cables and loses energy, using less current and, therefore, more potential
difference wastes less energy. So the reason for transmitting
electrical power this way is ultimately to minimize energy loss.