Electric Power system题目 第一句是Electric Power is a most conveni

Electric Power system题目 第一句是Electric Power is a most convenient clean safe

Electric Power and Power System Electric power is a most convenient clean safe and useful form of energy which supplies the major portion of energy needs of a modern society. At the present time the lack of electricity a blackout is newsworthy. Electric power is so vital to the lives of people that its unavailability causes inconvenience loss of production and danger to many individuals who are in operation in hospitals. A prolonged blackout which is inevitable when a growing load is combined with no generation additions could lead to social disorder and even national tragedy. Electric power is generated in power generating stations plants or simply known as power stations plants. Power generation means conversion of energy from a primary form to the electrical form. The current sources of nearly all the electrical energy generated come from: the conversion of chemical energy of fossil fuels nuclear fission energy and the kinetic energy of water which is allowed to fall through a difference of elevation they are referred to as fossil-fired power nuclear power and hydro power respectively. The voltage is usually transformed to a high level at the power plant and then via high voltage or extra-high voltage transmission lines the electric power is transmitted to general power consumption areas load areas. Electric power is transmitted at high voltage level either because of the distance or because of the amount of power or because of their combination. Before electric power is delivered to the electric power consumers or users there may be more voltage transformations. First at primary substations the voltage is reduced and then transmitted to local substations via subtransmission lines. Then another voltage reduction is experienced in local substations and the electric power is delivered to the power consumers loads via distribution systems. In distribution system electric power is directly delivered to electric users via feeders. Thus the entire system consisting electrically of power stations substation power consumers transmission lines and feeders is called a power system. In functional terms a power system includes power generation power transmission power transformation power distribution and power utilization. The connection between the power stations and loads is not a simple path but a complex network. The electric power utilities will plan design build and operate their power systems.
The Characteristics of Electric Power The electric power has unique technical characteristics which give the power industry certain unique business characteristics. a. Intangibility n.. The customer cannot directly detect a kilowatt-hour with any of his physical senses. The result of the kilowatt-hour of service light heat work output from a motor can be detected and for this he is willing to pay. Devices called kilowatt-hour meters are used to measure this intangible electrical energy delivered to customers. b. Quality. Although electricity is intangible it can be measured in amount and quality. The quality of service can be measured by service continuity or reliability uniformity n. of voltage at the proper level proper and uniform frequency of the alternating voltage. Also the shape of the voltage-time curve and its smoothness or wave shape is a measure of quality. c. Product storage. Unlike most businesses the electric power utility must create its product simultaneously with its use because there is no storage of electricity. The storage battery has chemical not electrical storage but the production of large blocks of power by chemical action so far is both technically and economically unsatisfactory. This simultaneous generation and transmission with use requires power system capacity to meet the load demand at whatever moment it occurs. Thus a maximum or peak demand of only a moment’s duration requires that the necessary equipment be in place throughout the entire year. d. Responsibility for power service. Because the utility delivers its product to the customer’s premises it must assume responsibility for the safe and reliable delivery of its product. The necessary transmission and distribution lines must be available and kept in service or promptly returned to service after interruption despite wind lighting ice kites and so on. e. Public safety. Electricity is a very useful servant when it is kept under control however it can be very destructive if control is lost because it can shock burn and kill. The utility must provide reasonably adequate protection for the public and its own skilled workers. Of the characteristics of electric power the primary concern of the electric power system engineers is to maintain a constant operating frequency. This job is normally assigned to an automatic control system that maintain at all times real power balance in the system. A mismatch in real power results in a frequency deviation n. . The next most important job is to maintain a proper profilen.throughout the system. This is accomplished by proper flows of reactive power on the various lines.
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