Home Letters Electricity is the most versatile energy source
If you’ve ever sat watching a thunderstorm, with mighty lightning bolts darting down from the sky, you’ll have some idea of the power of electricity. A bolt of lightning is a sudden, massive surge of electricity between the sky and the ground beneath. The energy in a single lightning bolt is enough to light 100 powerful lamps for a whole day, or to make about twenty thousand slices of toast!
Electricity is the most versatile energy source that we have. We have devised many gadgets and machines that run on electrical power to do useful work for us, and we also have developed many that simply amuse and entertain us. Homes and businesses have been using electricity for not much more than a hundred years.
Electricity has played a vital part in our past, but it could play a different role in our future. We have seen the mighty power lines that crisscross our communities and wiggle unseen beneath some of our streets carry electricity at enormously high voltages from power plants to our homes. It’s not unusual for power lines to be rated from 13,000 kv to 65,000 kv, but the appliances in our homes use voltages thousands of times smaller — typically just 110 to 250 volts. If you tried to power a toaster or a TV set from an electricity pylon, it would instantly explode! (Don’t even think about trying, because the electricity in overhead lines would almost certainly kill you) So there has to some way of reducing the high voltage electricity from power plants to the lower voltage electricity used by factories, offices, and homes. The piece of equipment that does this, humming with electromagnetic energy as it goes, is called a transformer. Let’s take a closer look at how it works!
Your first question is probably this: if our homes and offices are using photocopiers, computers, washing machines, and electric shavers rated at 110–250 volts, why don’t power stations simply transmit electricity at that voltage? Why do they use such high voltages? To explain that, we need to know a little about how electricity travels.
As electricity flows down a metal wire, the electrons that carry its energy jiggle through the metal structure, bashing and crashing about, and generally wasting energy like unruly schoolchildren running down a corridor. That’s why wires get hot when electricity flows through them (something that’s very useful in electric toasters and other appliances that use heating elements). It turns out that the higher the voltage electricity you use, and the lower the current, the less energy is wasted in this way. So, the electricity that comes from power plants is sent down the wires at extremely high voltages to save energy.
But there’s another reason too. Industrial plants have huge factory machines that are much bigger and more energy-hungry than anything you have at home. The energy an appliance uses is directly related (proportional) to the voltage it uses. So, instead of running on 110–250 volts, power-hungry machines might use 10,000 – 24,000 volts. Smaller factories and machine shops may need supplies of 400 – 440 volts or so. In other words, different electricity users need different voltages. It makes sense to ship high-voltage electricity from the power station and then transform it to lower voltages when it reaches its various destinations.
Even so, centralised power stations are still very inefficient. About two-thirds of the energy that arrives at a power plant in the form of raw fuel is wasted in the plant itself and on the journey to your home.
As we’ve already seen, there are lots of huge transformers in our communities, towns and cities, where the high-voltage electricity from incoming power lines is converted into lower-voltages. But there are lots of transformers in your home also. Big electric appliances such as washing machines and dishwashers use relatively high voltages of 110–240 volts, but electronic devices such as laptop computers and chargers for MP3 players and mobile cellphones use relatively tiny voltages: a laptop needs about 15 volts, an iPod charger needs 12 volts, and a cellphone typically needs less than 6 volts when you charge up its battery. So electronic appliances like these have small transformers built into them (often mounted at the end of the power lead) to convert the 110–240 volts of domestic supply into a smaller voltage they can use.
If you’ve ever wondered why things like cellphones have those big, fat chunky power cords, it’s because they contain transformers!