One of the most important characteristics of electrical energy is its ability to be transferred over long distances. High-voltage electric power distribution lines can be found scattered everywhere throughout the United States. They are a common reminder of our dependence on electricity. A great deal of engineering has gone into making those power distribution lines reliable and efficient. The enormous amount of potential energy harnessed by a power station like the Grand Coulee Dam is of no value to a factory ten miles away unless that energy can be transferred efficiently from the dam to the factory. This chapter will explore how electric currents function and how we control them.
Electrical power is the product of voltage, which is measured in watts, and current, which is measured in amperes. Resistance to the flow of electricity is measured in ohms. Anything in an electrical circuit that makes use of the flow of electricity provides some resistance. Electrical resistance within a wire is dependent not only on the material of the wire, but also on the length of the wire and the amount of current flowing through it. By converting electrical power to high voltage and low current, power companies can efficiently transfer energy over great distances with little loss. The power must be converted back at its destination for use in homes and businesses. Circuit breakers and fuses control the flow of current through a circuit and provide a measure of protection against excessive heat that may result from faulty circuits.