The Nature of Electricity
Electricity is a little different from the other sources of energy that we talk about. Unlike coal, petroleum, or solar energy, electricity is a secondary (not primary) source of energy. That means we must use other (primary) sources of energy to make electricity. It also means we can’t classify electricity as a renewable or nonrenewable form of energy. The energy source we use to make electricity may be renewable or nonrenewable, but electricity is neither.
Almost all electricity made in the United States is generated by large, central power plants. These plants typically use coal, nuclear fission, natural gas, or other energy sources to produce heat energy which superheats water into steam. The very high pressure of the steam (75-100 times normal atmospheric pressure) turns the blades of a turbine. (At a hydroelectric plant, the force of falling water turns the blades.) The blades are connected to a generator which houses a large magnet surrounded by a coiled copper wire. The blades spin the magnet rapidly, rotating the magnet inside the coil and producing an electric current. The steam, which is still very hot but back to normal pressure, now goes to a condenser where it is cooled into water by passing it through pipes circulating over a large body of water or cooling tower. The water then returns to the boiler to be used again. Power plants can capture some of the heat from the cooling stream. In old plants, the heat was simply wasted.
Moving Electricity from power Plants to Homes
We are using more and more electricity every year. One reason electricity is used so much, it’s easy to move from one place to another. Electricity can be produced at a power plant and moved long distances before it is used. Let’s follow the path of electricity from power plant to a light bulb in your home.
- First, the electricity is generated at the power plant. Next, it goes by wire to a transformer that “steps up” the voltage. A transformer step up the voltage of electricity from the 2,300 to 22,000 volts produced by a generator to as much as 765,000 volts (345,000 volts is typical). Power companies step up the voltage because less electricity is lost along the lines when the voltage is high.
- The electricity is then sent on a nationwide network of transmission lines made of aluminum. Transmission lines are the huge tower lines you may see when you’re on a highway. The lines are interconnected. Should one line fail, another will take over the load.
- Step-down transformers located at substations along the lines reduce the voltage to 12,000 volts. Substations are small buildings or fenced-in yards containing switches, transformers, and other electrical equipment.
- Electricity is then carried over distribution lines which bring electricity to your home. Distribution lines may either by overhead or underground. Overhead distribution line are the electric lines that you see along streets.
- Before electricity enters your house, the voltage is reduced again at another transformer, usually a large gray can mounted on an electric pole. This transformer reduces the electricity to the 120 volts that are needed to run the light bulb in your home.
- Electricity enters your house through a three-wire cable. The “live wires” are then brought from the circuit breaker or fuse box to power outlets and wall switches in your home. An electric meter measures how much electricity you use so the utility company can bill you.
- The time it takes for electricity to travel through these steps–from the power plant to the light bulb in your home–is a tiny fraction of one second!
Power to the People
Everyone knows how important electricity is to our lives. All it takes is a power failure to remind us how much we depend on it. Life would be very different without electricity–no more instant light from flicking a switch; no more television; no more refrigerators; or stereos; or video games; or hundreds of other conveniences we take for granted. You could almost say the American economy runs on electricity. It’s the business of electric utility companies to make sure electricity is there when we need it. How do they do it? First, some terms: reliability, capacity, base load, power pools, and peak demand.
- Reliability is the capability of a utility company to provide electricity to its customers 100 percent of the time. A reliable electric service is without blackouts or brownouts. To ensure uninterrupted electric service, laws require most utility companies to have 15-20 percent more capacity than they need to meet peak demands. This means a utility company whose peak load is 12,000MW, would need to have about 14,000 MW of installed electrical capacity. This helps ensure there will be enough electricity to go around even if equipment were to break down on a hot summer afternoon.
- Capacity is the total quantity of electricity a utility company has online and ready to deliver when people need it. A large utility company may operate several plants to generate electricity for it customers. A utility company has seven 1,000-MW (megawatt) plants, eight 500-MW plants, and 30 100-MW plants has a total capacity of 14,000-MW.
- Base-load Power is the electricity generated by utility companies around-the-clock, using the most inexpensive energy sources–usually coal, nuclear, and hydropower. Base-load power stations usually run at full or near capacity,
- When many people want electricity at the same time, there is a Peak Demand. Power companies must be ready for peak demands so there is enough power for everyone. During the day’s peak, between 12:00 noon and 6:00 p.m., additional generating equipment has to be used to meet increased demand. This equipment is more expensive to operate. These peak load generators run on natural gas, diesel or hydro and can be running in seconds. The more this equipment is used, the higher our utility bills. By managing the use of electricity during the peak hours, we can help keep costs down.
- The use of Power Pools is another way electric companies make their systems more reliable. Power pools link utilities together so they can share power as it is needed. A power failure in one system can be covered by a neighboring power company until the problem is corrected. There are nine regional power pool networks in North America. The key is to share power rather than lost it.
The reliability of U.S. electric service is excellent, usually better than 99 percent. In some countries, electric power may go out several times in a day. Power outages in the United States are usually caused by such random occurrences as lightning, a tree limb falling no electric wires, or a car hitting a utility pole.