Large Diesel Generators

Large diesel generators principles & guide to help you know more about diesel generators, backup power generators & electricity.

The basic principles of Large Diesel Generators Voltage is a measure of the strength of an electrical supply. A voltage may exist even when no current is flowing. In older textbooks you will find terms like `electrical potential' or `electro-motive force', which gives a better feel for what voltage means. Strictly, a voltage is only defined between two points. When only one point is specified, we tacitly assume that the other point is the earth (which means exactly what it says: the ground beneath our feet).

 The earth is not a very good conductor of electricity, but there's an awful lot of it, which makes up for this to a certain extent. So when I say `there's 230 volts at this point', what I really mean is that the voltage difference between this point and earth is 230 volts (it's a bit more complicated than this in practice, as we shall see).

Voltage is measured in volts, which is abbreviated to `V'. So `230V' means `230 volts'. The mathematical symbol for voltage is also `V'. Incidentally, although you'll hear electricians talking about `240 volt' mains, in fact our mains supply voltage has been 230 volts for about ten years, to make our electrical equipment compatible with that of the rest of Europe.

To get an alternating current, we need an alternating voltage. So the electrical mains voltage will cycle from about 325 volts, to zero, to -325 volts, then back to zero, and so on, 50 times per second. This is shown in figure 1

When only one point is specified, we tacitly assume that the other point is the earth (which means exactly what it says: the ground beneath our feet). The earth is not a very good conductor of electricity, but there's an awful lot of it, which makes up for this to a certain extent. So when I say `there's 230 volts at this point', what I really mean is that the voltage difference between this point and earth is 230 volts (it's a bit more complicated than this in practice, as we shall see).