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Electric Power System and Power System Automatic
ampereElectirc Prower Systems,components that transform other types of energy into electrical energy and transmit this energy to a consumer. The production and transmission of electricity relavtively efficient and inexpensive,although unlike other forms of energy,electricity is not easily stored-up and thus must generally be ud as it is being produced.
Components of an Electric Power System
A modern electric power system consists of six main components:(1)the power station, (2)a t of transformers to rai the generated power to the high voltages ud on the transmission lines,(3)the transmission lines,(4) the substations at which the power is stepped down to the voltage on the distribution lines,(5)the distrib ution lines,and(6)the transformers that lower the distribution voltage to the level ud by the consumer's equipment.
Power Station The power station of a power system consist of a prime mover, such as a turbine driven by water,steam,or combustion gas that operate a system of electric motors and generators.Most of the world's electric power is generated in steam plants driven by coal,oil,nuclear energy,or gas.A smaller percentage of the world's electric power is generated by hydroelectric(waterpower ),diel,and i
nternal-combustion plants.
Transformers Modern electric power system u transformer to convert electricity into different voltage.With transformers,each stage of the system can be operated at an appropriate voltage.In a typical system, the generators at the power station deliver a voltage of from 1,000 to 26,000 volts(V ).Transformers step this voltage up to values ranging form 138,000to 765,000 V for the long-distance primary transmission line becau higher voltage can be transmitted more efficiently over long distances.At the substation the voltage may be transformed down to levels of 69,000 to 138,000 V for further transfer on the distribution system. Another t of transformers step the voltage down again to a distribution level such as 2,400 or 4,160 V or 15,27,or 33 kilovolts(KV ).Finally the voltage is transformed once again at the distribution transformer near the point of u to 240 or 120 V.
Transmission Lines The line of high-voltage transmission systems are usually compod of wires of copper, aluminum, or copper-clad or aluminum-clad steel, while are suspended from tall latticework towers of steel by strings of porcelain insulator. By the u of clad steel wires and high towers, the distance between towers can be incread, and the cost of the transmission line thus reduced.In modern installation with esntially straight paths, high-voltage lines may be built with as few as few as six towers to the kilometre. In some areas high-voltage lines are suspended from tall wooden pole
star spaced more cloly together.
domesticatedFor lower voltage distribution lines, wooden poles are generally ud rather than steel towers,In cities and other areas where open lines create a safety hazard or are considered unattractive, insulated underground cables are ud for distribution.Some of the cables have a hollow core through which oil circulates under low pressure. The oil provides temporary protection from water damage to the enclod wires
ballshould the cable develop a leak. Pipe-type cables in which three cables are enclod in a pipe filled with oil under high pressure (14 kg per sq cm/200psi )are frequently ud. The cables are ud for transmission of current at voltages as high as 345,000V(or 345kV ).
Supplementary Equipment Any electric-distribution system involves a large amount of supplementary equipment to protect the generators, transformers, and the transmission lines themlves. The system often include devices designed to regulate the voltage or other characteristics of power delivered to consumers.
To protect all elements of a power system from short circuit and overloads, and for normal switching operation, circuit breakers are employed.The breakers are large switches that normal activated au谀词
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tomatically in the event of a short circuit or other condition that produces a sudden ri of current.Becau a current forms across the terminals of the circuit breaker at the moment when the current is interrupted, some large breakers (such as tho ud to protect a generator or a ction of primary transmission line )are immerd in a liquid that is a poor conductor of electricity, such as oil, to quench the current. In large air-type circuit breakers, as well as in oil breakers, magnetic fields are ud to break up the current. Small air-circuit breakers are ud for protection in shops, factories, and in modern home installations. In residential electric wiring, fus were once commonly employed for the same purpo.A fu consists of a piece of alloy with a low melting point, inrted in the circuit, which melts, breaking the circuit if the current ris above a certain value.Most residences now u air-circuit breakers.
Power Failures
In most parts of the world, local or national electric utilities have joined in grid systems. The linking grids allow electricity generated in one area to be shared with others.Each utility that agrees to share gain an incread rerve capacity, u of large, more efficient generators, and the ability to respond to local power failures by obtaining energy from a linking grid.
文明与我同行The interconnected grids are large, complex systems that contain elements operated by different groups. The system offer the opportunity for economic savings and improve overall reliability but can create a risk of widespread failure. For example, the worst blackout in in the history of the United Stated and Canada occurred August 14, 2003, when 61,800 megawatts of electrical power was lost in an area covering 50 million people.(one megawatt of electricity is roughly the amount needed to power 750 residential home.)The blackout prompted calls to replace aging equipment and raid questions about the reliability of the national power grid.
Despite the potential for rare widespread problems, the interconnected grid system provides necessary backup and alternate paths for power flow, resulting in much higher overall reliability than is possible with isolated system. National or regional grids can also cope with unexpected outages such as tho caud by storms, earthquakes, landslides, and forest fires, or due to human error or deliberate acts of sabotage.
Power Quality
In recent years electricity has been ud to power more sophisticated and
technically complex manufacturing process, computers and computer networks, and a variety of ot
her high-technology consumer goods. The products and process are nsitive not only to the continuity of power supply but also to the constancy of electrical frequency and voltage. Conquently, utilities are taking new measures to provide necessary reliability and quality of electrical power, such as by providing additional electrical equipment to assure that the voltage and other characteristics of electrical power are constant.
V oltage Regulation Long transmission lines have considerable inductance and capacitance. When a current flows through the line, inductance and capacitance have the efficient of varying the voltage on the line as the current varies. Thus the supply voltage varies with the load. Several kinds of devices are ud to overcame this undesirable variation in an operation called regulation of the voltage. The devices include induction regulators and three-pha synchronous motors (called synchronous condenrs), both of which vary the effective amount of inductance and capacitance in transmission circuit.
Inductance and capacitance react with a tendency to nullify one another. When a load circuit has more inductive than capacitive reactance, as almost invariably occurs in large power systems, the amount of power delivered for a given voltage and current is less than when the two are equal. The ratio of the two amounts of power is called the power factor. Becau transmission-line loss are
proportional to current, capacitance is added to the circuit when possible, thus bringing the power factor as nearly as possible to 1. For this reason, large capacitors are frequently inrted as a part of power-transmission systems.
World Electric Power Production Over the period from 1950 to 2003, the most recent year for which data are available, annual world electric power production and consumption ro from slightly less than 1trillion kilowatt-hours(KW.H )to 15.9 trillion kW-h. A change also took place in the type of power generator. In 1950 about two-thirds of the world's electricity came from steam-generating source and about one-third from hydroelectric source. In 2003 thermal power produced 65 percent of the power ,but hydroelectric had declined to 17 percent,and nuclear power accounted for 16percent of the total. The growth in nuclear power slowed in some countries, notably the United States, in respon to concerns about safety. Nuclear plants generated 20 percent of U.S. Electricity in 2003; in France , the world leader, the figure was 78 percent.
Conrvation
Much of the world's electricity is produce from the u of nonrenewable resource, such as natural gas, coal, oil, and uranium. Coal, oil, and natural gas contain carbon, and buring the fossil fuels co
ntribution to global emission of carbon dioxide and other pollutants. Scientists believes that carbon dioxide is the principal gas responsible for global warming, a steady ri in earth's surface temperature.
离心泵分类Consumer of electricity can save money and help protect the environment by elimination unnecessary u of electricity, such as turning off lights when leavings a room. Other conrvation methods include buying and using energy-efficient appliance and light bulbs, and using appliances, such as washing machines and dryers,
at off-peak production hours when rates are lower. Consumers may also consider environment measure such as purchasing "green power " when it is offer by a local utility. "green power" is usually more expensive but relies on renewable and environment friendly energy source, such as wind turbines and geothermal power plants.
Overview
Power provides constantly deal with demands to increa productivity and reduce costs. This translates into the need for administrators, engineers, operators, planners, field crews and others to collect and act on decision making information. Power system vendors are following a trend to mack
device smarter so they can create and communicate this information. The term "power system " describes the collection of device that make up the physical systems that generate, transmit, and distribute power. The term "instrumentation and control system "refers to the collection of devices that monitor, control, and protect the system.
Power system automation refers to using refers to using I&C devices to perform automatic decision making and control of the power system.
Data Acquisition Data acquisition refers to acquiring ,or collecting, data. This data is collected in the form of measured analog current or voltage values or the open or clod status of contact points. Acquired data can be ud locally within the device collecting it, nt to another device in a substation, or nt from the substation to one or veral databas for u by operators engineers, planners, and administrators.
Power System Supervision Computer process and personnel supervi, or monitor, the condition and status of the power system using this acquired data. Operators and engineers monitor the information remotely on computer display and graphical wall displays or locally, at the device, on front-panel displays and laptop computers .
Power System Control Control refers to nding command message to a device to operate the I&C and power system device. Traditional supervisory control and data acquisition(SCADA )system rely on operators to supervisory the system and initiate command from an operators console on the master computer. Field personnel can also control device using front-panel push buttons or a laptop computer.
Power System Automation System automation is the act of automation control the power system via automation process within computer and and intelligent I&C device. The process rely on date acquisition, power system supervisory, and power system control all working together in a coordinate automation fashion. The commands are generator automation and then transmit in the same fashion as operator initiated commands.
I&C System IEDS I&C devices built using microprocessors are commonly referred to as intelligent electricity device (IEDS ). Microprocessor are single chip computer that allow the devices into which they are built to process data, accept command, and communicate information like a computer. Automatic process can be run in the IEDS,and communications are handled through a rial port like the communications ports on a computer. IEDS are found in the substation and on the pole-top.
Equipment for Power System Automatic
Power system automatic includes a variety of equipment. The principal items are listed and briefly described below.
Instrument Transformer Instrument transformer are ud to n powe r system current and voltage values. They are physical connected to power system apparatus and convert the actual power system signals, which include high voltage and current magnitudes, down to lower signal levels.
Transducer Transducer convert the analong output of an instrument transformer from one magnitude to another or from one value type to another, such as from an ac current to dc voltage.
Remote Terminal Unit As the name implies, a remote terminal device , RTU, is an IDE that can be installed in a remote location, and acts as a terminal point for field contacts. A dedicated pair of copper conductors are ud to n every contacts and transducer value. The conductors originate at the power system device, are installed in trenches or overhead cable trays and are then terminal on panels within the RTU. The RTU can transfer collected data to other device and receive data and control command from other devices through a rial port. Ur programmable RTUs are referred to as "smart RTUs ".
Communications Port Switch A communications switch is a device that switches between veral rial Ports when it is told to do so. The remote ur initiates communicate with the port switch via a connection to the substation, typically a lead line or dial-up telephone connection. Once connected, the ur can route their communications through the port switch to one of the connected substation IEDS. The port switch merely "pass through "the IED communications.
Meter A meter is an IED that is ud to create accurate measurements of power system current, voltage, and power values. Metering values such as demand and peak are saved within the meter to create history information about the activity of the power system.
欢迎光临英语Digital Fault Recorder A digital fault recorder ,is an IED that recorders information about power system disturbance. It is capable of storing data in a digital format when triggered by conditions detected on the power system. Harmonics, frequency, and voltage are examples of data captured by DFRS.
Load Tap Changer(LTC ) Load tap changers are devices ud to Changer the tap position on transformers. The devices work automatically or can be controlled via another local IED or from a remote operator or process.
Reclor Controller Recolr controllers remotely control the operation of automatic mated reclors and switches. The devices monitor and store power system conditions and determine when to perform control actions.They also accept commands from a remote operator or process.小说 mp3
Time Synchronization Source A time synchronization source is an IED that creates a time-of-day values which is then broadcast to the IEDS in order to t all their clocks to the same time.
Protocol Gateway IEDS communicate over rial connected by speaking a particular language or protocol. A protocol gateway converts communications from
