Emergency Generator I

Basic principles of backup emergency generators, diesel power & backup electric generators & electricity by Bowerspower.

The basic principles of Emergency Backup Generators and electricity,

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

An electrical current is the flow of electricity around an electrical circuit. The flow of electricity follows similar principles to the flow of water in pipes, as we shall see, with the exception that an electrical system must make a complete circuit. The circuit will contain a power source of some kind; in mains wiring the power source is the national electrical distribution system which is mostly outside our control.

Of course, the distribution company don't run wires directly from the power station to our houses: there is all manner of other stuff between them and us, but that isn't all that important. For most cases you can proceed as if a small power station was connected directly to your house.

Diesel Generator    

In domestic electrical work, current is generally measured in amps. Currents you will encounter in practice range from about 0.5 amps (through a lightbulb) to about 40 amps (an electric shower). Technically `amps' is short for `Ampиres', but the full name is now rarely used. The mathematical symbol for current, as it is written in calculations, is not `C' (for current) or `A' (for amps) but in fact `I'. This is just because the symbols `C' and `A' are reserved for other things. You will occasionally come across currents measured in milliamps (`mA' for short). A milliamp is a thousandth of an amp. For example, most earth-leakage breakers used in domestic wiring trip at 30 mA, which is about one thirtieth of an amp.

To get an electrical current to flow, we need a power source, and some sort of conductor. A conductor is defined as anything that can carry a flow of electricity. In electrical practice, conductors tend to be copper wire or copper bars, usually hidden away inside plastic sleeves. The sleeves are insulators, that is, materials that prevent the flow of electricity. It is the insulator that keeps the electrical current where it belongs - inside the cable.

You can be an electrician without knowing much about electricity. It seems odd, but it's true. But if you do know the principles, you can do safe and practical work without memorizing a whole heap of regulations, because they're mostly derived from standard principles anyway. The key features of electricity are voltage, current, resistance, power, and frequency.