Electrical generators

The Fawley refinery generates electricity which is fed into the National Grid. The generators are the same as any generator. They use the principals of electromagnetism to generate a voltage which can drive an electric current around the system. Let's see how this works.

Interactive graphic of simple generator
Pushing a magnet in and out of a coil to get an voltage.

The picture shows a magnet near a coil of wire. The coil is connected to a sensitive meter which shows zero current.

If we push the magnet into the coil, the meter flicks to the right.

If we pull it out again, the meter flicks to the left.

Pushing it in and out makes the meter flick left then right.

We call this effect electromagnetic induction. We are inducing a voltage by moving a magnet in a coil.

Notice that when the magnet is stationary, there is no voltage. This makes sense: we have to put some effort in to get a voltage out. If we don't put anything in, we don't get anything out.

We only get a voltage out when the magnet is moving. Therefore, if we want to get a continuous voltage, we have to keep the magnet moving.

One way to do this is to put the magnet on a spindle next to the coil and turn it.

The picture shows a magnet on a crank shaft. When we turn the handle the meter flicks to the right and left.

We have to keep turning the magnet to keep getting a voltage out. I.e. we have to put mechanical work in to get electrical work out.

Notice that the voltage keeps changing directions - it goes backwards and forwards. We call this an alternating voltage. When we connect it to, for example, a lamp, it will drive an alternating current (a.c.) through the lamp.

The mains voltage is alternating. It goes backwards and forward 50 times a second (we say it has a frequency of 50 Hz). For each cycle, a lamp goes on twice (once for the forward current and once for the backwards current). So the lights in your house go on and off a hundred times a second.

Interactive graphic of handle generator
Generating steam and electricity.

The generators in a power station are, of course, much bigger than this. Some of them use a magnet moving inside a coil - a bit like this one. Others use a moving coil in a magnetic field - a bit like an electric motor in reverse. However, they both work on the same principle: when the magnetic field in a coil changes, we get a voltage out of the coil.