Electrical power can be produced in many ways, including chemical reactions, heat, light, or mechanical energy. Most electrical power produced today is through hydroelectric plants and nuclear energy, and by burning coal, oil, or natural gas. Fossil fuel and nuclear-fission plants use steam turbines to deliver the mechanical energy required to rotate large three-phase generators, which produce massive quantities of electrical power. Generators used in such facilities usually are classified as high-speed units, operating at 3600 rpm to produce a 60 Hz output frequency. Hydroelectric systems use hydraulic turbines, mounted vertically to intercept the flow of water to produce electrical energy. Most hydroelectric facilities use low speed generators, operating at from 120 to 900 rpm to produce 60 Hz. It follows that a larger number of poles are required for a low-speed generator.
Fossil fuels, used as a source of heat, are burned to produce steam in a boiler system. The steam then drives one or more generators. Coal and coke are used commonly to produce energy in this manner. Other fossil fuel sources include oil and natural gas.
A nuclear power plant is basically a fossil fuel facility with a nuclear power source to produce heat and then steam. Nuclear fission is a complex process that results in the division of the nucleus of an atom into two nuclei. This splitting of the atom is initiated by bombardment of the nucleus with neutrons, gamma rays, or other charged particles.
A hydroelectric system is the simplest of all power plants. Flowing water from a reservoir is channeled through a control gate that directs water to the blades of a hydraulic turbine. The turbine, in turn, drives one or more generators. Although simple in design and efficient in operation, hydroelectric systems are limited by the availability of a water reservoir.
Concern about the burning of fossil fuels and the safety of nuclear power has led to the development of alternative fuel sources for turbine-driven power plants. Power-generating systems now in operation include:
• Geothermal systems, which utilize the heat of a molten mass in the interior of the earth to produce steam, which drives a turbine generator. Such systems are efficient and simple, but their placement is limited to areas of geothermal activity.
• Wind systems, which use a number of small generators mounted on supports and attached to propeller-type blades to intercept prevailing winds. Naturally, generator output is determined by wind activity, limiting the use of these systems on any large scale.
Significant variations in load requirements must be satisfied at different times by a generating plant.
Because of wide variations in load demands, much of the generating capability of a facility may be unused during low-demand periods. Two mathematical ratios commonly are used to measure utility service:
- Load factor: The average load for a given period divided by the peak load for that same period.
- Capacity factor: The average load for a given period divided by the output capacity of the power plant.