ELECTRIC POWER TRANSMISSION AND DISTRIBUTION

Date: 2015-10-07; view: 799.

Electric power transmission, a process in the delivery of electricity to consumers, is the bulk transfer of electrical power. 1_____________ Electricity distribution is the delivery from the substation to the consumers. Electric power transmission allows distant energy sources (such as hydroelectric power plants) to be connected to consumers in population centers, and may allow exploitation of low-grade fuel resources that would otherwise be too costly to transport to generating facilities.

Due to the large amount of power involved, transmission normally takes place at high voltage (110 kV or above). 2_____________ Underground power transmission is used only in densely populated areas due to its high cost of installation and maintenance, and because the high reactive power produces large charging currents and difficulties in voltage management.

3_______________ However, for reasons of economy, the network is not a mathematical grid. Redundant paths and lines are provided so that power can be routed from any power plant to any load center, through a variety of routes, based on the economics of the transmission path and the cost of power. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line, which, due to system stability considerations, may be less than the physical or thermal limit of the line. 4______________ However, in some places the gaming of a deregulated energy system has been disastrous, such as that which occurred during the California electricity crisis of 2000 and 2001.

Power delivered by transmission circuits must be stepped down in facilities called substations to voltages more suitable for use in industrial and residential areas. On transmission systems, these facilities are commonly called bulk-power substations; on or near factories or mines, they are termed industrial substations; and where they supply residential and commercial areas, distribution substations. 5_______________ There is also instrumentation, control devices and other apparatus related to specific function in the power system.

That part of the electric power system that takes power from a bulk-power substation to consumers' switches, commonly about 40% of the total plant investment, is called distribution. Primary distribution circuits usually operate at 4,160-34,500 volts line-to-line and may be overhead open wire on poles, overhead or aerial cable, or underground cable. 6_____________ Smaller consumers are supplied through numerous distribution transformers. At conveniently located distribution transformers in residential and commercial areas, the voltage is stepped down again to 120 and 240 volts for secondary lines, from which service drops or loops extend to every consumer's lights and appliances. These low voltages are known as utilization voltages.