It used to be the case that every town had its own power station that made electricity for that place only. Eventually it was thought more sensible to build huge power stations for the whole country and connect them up using power lines. The problem is that miles and miles of cable waste a lot of energy. Electric current heats the wires slightly so that they dissipate thermal energy to the surroundings. If you use transformers before the electricity goes into the cables, they use electromagnets to increase the voltage. This also reduces the current so there is less heating of the cables. Less energy is wasted so we say that the system is more efficient. However, you wouldn't want a huge voltage like 425000V in your home. More transformers are used to bring the voltage back down to normal. These transformer are called substations. There is a huge substation in the picture above. It is just above the railings. This substation is for the chemical factories on the outskirts of Runcorn in Cheshire, just south of the River Mersey. It also sorts out the voltage for the ring of cables that go round to Liverpool and back. The National Grid is said to be both the overhead power lines AND the transformer substations. Without both of these it would impossible to send electricity round the country.
