In today's modern world, we largely take electricity for granted. Yet, nearly everything around us is operated by it. Our homes are heated and lit with electricity. Computers, TV sets, game consoles and many more appliances are operated by electricity. Often, we plug these things into the wall, giving little thought to where the electricity that powers these things comes from.
Electricity is produced at power plants in large quantities. Each plant can produce enough power to provide electricity to many thousands of homes. The problem is getting the electricity from these power plants to the homes and businesses that make use of it. This is where the distribution grid comes into the picture. Running from power plants to consumers is a large network of power lines and electrical equipment. In fact, every power plant in the nation is connected to form one massive distribution grid. However, this grid is simply not wires connecting power plants and consumers. There are many steps in between.
First, we must understand the nature of the power being transmitted. There are two types of electricity that are used in power transmission: alternating current (AC) and direct current (DC). In nature, electricity exists in DC form. Lightning is an example of direct current at very high voltage. Direct current is such that its polarity is constant - it only travels in one direction, positive to negative. Alternating current different in that the polarity is constantly switching, from positive to negative and back again. This means the current is reversing directions every cycle.
Both DC and AC power can be transmitted over distribution power lines. However, DC is limited in the fact that its voltage cannot be easily changed. High voltage would destroy home appliances, while low voltage would be too costly to transmit. The higher the voltage, the further power can be transmitted, and the more power can be transmitted over thinner lines. For this reason, power is distributed as AC. The voltage of AC can easily be changed using a device called a transformer. The voltage is increased for easy transmission over power lines, and then is decreased for use in homes and business. Because of AC, power can easily be transferred in bulk quantity over great distances, significantly reducing distribution costs.
To further save on costs, AC power is transmitted in a three-phase system. In this system, three wires are used. Each wire switches polarity at a different time than the other, so that current is always flowing between them. For example two wires can be positive (+) and the other will be negative (-). Two wires can also be negative at a given time and one will be positive. This eliminates the need for a return (neutral) wire. Otherwise, a similar system would need six wires instead of three. This again significantly reduces the cost to transmit power over long distances.
These innovations in distribution power lines allow power to be easily delivered to homes and businesses around the nation in an affordable manner.