Electricity - Electricity Defined

Electricity is a form of energy resulting from the movement of charged particles, such as electrons (negatively charged subatomic particles) and protons (positively charged subatomic particles). Static electricity is caused by friction, when one material rubs against another and transfers charged particles. The zap you might feel and the spark you might see when you drag your feet along the carpet and then touch a metal doorknob is static electricity—electrons being transferred between you and the doorknob.

Electric current is the flow of electric charge; it is measured in amperes (amps). Electrical power is the rate at which energy is transferred by electric current. A watt is the standard measure of electrical power, named after the Scottish engineer James Watt. The term "wattage" refers to the amount of electrical power required to operate a particular appliance or device. A kilowatt is a unit of electrical power equal to one thousand watts, while a kilowatt-hour is a unit of electrical work equal to that done by one kilowatt acting for one hour.

Electrical Capacity

The generating capacity of an electrical plant, measured in watts, indicates its ability to produce electrical power. A one-thousand-kilowatt generator running at full capacity for one hour supplies one thousand kilowatthours of power. That generator operating continuously for an entire year could produce 8.76 million kilowatt-hours of electricity (1,000 kilowatts × 24 hours/day × 365 days a year). However, no generator can operate at 100% capacity during an entire year because of downtime for routine maintenance, outages, and legal restrictions. On average, about one-fourth of the potential generating capacity of an electrical plant is not available at any given time.

Electricity demands vary daily and seasonally, so the continuous operation of electrical generators is not necessary. Utilities depend on steam, nuclear, and large hydroelectric plants to meet routine demand. Auxiliary gas, turbine, internal combustion, and smaller hydroelectric plants are normally used during short periods of high demand.

An Electric Power System

An electric power system has several components. Figure 8.1 illustrates a simple electric system. Generating units (power plants) produce electricity, transmission lines carry electricity over long distances, and distribution lines deliver the electricity to customers. Substations connect the pieces of the system together, while energy control centers coordinate the operation of all the components.