DK Science & Technology: Electricity Supply
Electricity has revolutionized the way we use energy. It can be generated in large POWER STATIONS far away from towns and cities, and distributed cleanly to homes, offices, and factories through a network of power lines.
To make electricity, the coils inside a generator are turned by turbines. Most large generators are powered by turbines spun around by high-pressure steam. The steam is produced in boilers heated by fossil fuels (or in a nuclear reactor). Water turbines are also used to turn the generators in hydroelectric power stations.
From the power stations, electricity is fed into a vast network of cables and wires called the power grid. Electricity travels through the grid into almost every room in the system. Controlling the power in the grid is complex. Engineers must try to make sure that enough power is available whenever it is needed.
Current is produced in two forms: direct current (DC) and alternating current (AC). Direct current (produced by batteries) only flows in one direction. Alternating current (produced by power stations) switches back and forth, reversing direction regularly. An AC current switches back and forth 50 or 60 times a second.
Electricity generated by the power stations is fed into a grid of interconnecting power lines. These take the energy wherever it is required. When you switch on a light, you have no way of knowing which power station the electricity came from.
A large, coal-fired power station may produce a continuous flow of up to 1,000 MW (megawatts) of electricity. That’s enough power to light 20 million light bulbs, or meet all the power needs of a small city.
Electric current is carried around the country by power lines. Most power lines are slung high above the ground, on tall metal pylons. In towns or cities, the lines may go underground. Power lines carry electricity at 400,000 volts—thousands of times greater than the voltage received in our homes.
At various stages along the way, the power lines feed into substations. These contain transformers and heavy-duty switching gear that reduce (lower) the voltage to safer levels and direct power to where it is needed.
Large industrial plants use tremendous amounts of electrical energy. Many have their own dedicated power stations.
Power stations work day and night to produce the electricity that provides us with heat and light, and drives all kinds of machines, from hair dryers and refrigerators to televisions and trains.
Electricity from a power station is boosted from 25,000 volts to 400,000 volts to travel along power lines. But the voltage must be lowered before it is safe to use. Transformers reduce the voltage in stages to different levels to supply factories, subways, farms, hospitals, offices, homes, and highways.