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1、Chapter 6Electric Power SystemsSection 3 Operation and Control of Power Systemsn Textn New Words and Expressionsn Exercisesn Endn Translation of Numeral WordsSection 3 Operation and Control of Power Systems The purpose of a power system is to deliver the power the customers require in real time,on d
2、emand,within acceptable voltage and frequency limits,and in a reliable and economic manner.In normal operation of a power system,the total power generation is balanced by the total load and transmission losses.The system frequency and voltages on all the buses are within the required limits,while no
3、 overloads on lines or equipment are resulted.However,loads are constantly changed in small or large extents,so some control actions mustSection 3 Operation and Control of Power Systemsbe applied to maintain the power system in the normal and economic operation state.Optimal economic operation It is
4、 an important problem how to operate a power system to supply all the(complex)loads at minimum cost.The basic task is to consider the cost of generating the power and to assign the allocation of generation(PGi)to each generator to minimize the total production cost while satisfying the loads and the
5、 losses on the transmission lines.The total cost of operation includes fuel,labor,andSection 3 Operation and Control of Power Systemstoday may not be available in the future when its use might be more advantageous.Even without the element of the prediction involved,the problem of minimizing producti
6、on cost over time becomes much more complicated.It should be mentioned that economy of operation is not the only possible consideration.If the optimal economic dispatch requires all the power to be imported from a neighboring utility through a single transmission link,considerations of system securi
7、ty might preclude that solution.Section 3 Operation and Control of Power SystemsWhen water used for hydro-generation is also used for irrigation,nonoptimal releases of water may be required.Under adverse atmospheric conditions it may be necessary to limit generation at certain fossil-fuel plants to
8、reduce emissions.In general,costs,security and emissions are all areas of concern in power plant operation,and in practice the system is operated to effect a compromise between the frequently conflicting requirements.Section 3 Operation and Control of Power Systems Power system control Power system
9、control is very important issue to maintain the normal operation of a system.System voltage levels,frequency,tie-line flows,line currents,and equipment loading must be kept within limits determined to be safe in order to provide satisfactory service to the power system customers.Voltage levels,line
10、currents,and equipment loading may vary from location to location within a system,and control is on a relatively l ocal basis.Section 3 Operation and Control of Power SystemsActive power and frequency controlFor satisfactory operation of a power system,the frequency should remain nearly constant.Rel
11、atively close control of frequency ensures constancy of speed of induction and synchronous motors.Constancy of speed of motor drives is particularly important for satisfactory performance of all the auxiliary drives associated with the fuel,the feed-water and the combustion air supply systems.In a n
12、etwork,considerable drop in frequency could result in high magnetizing currents in induction motors and transformers.The extensive use of Section 3 Operation and Control of Power Systemselectric clocks and the use of frequency for other timing purpose require accurate maintenance of synchronous time
13、 which is proportional to integral of frequency.As a consequence,it is necessary to regulate not only the frequency itself but also its integral.The frequency of a system is dependant on active power balance.As frequency is a common factor throughout the system,a change in active power demand at one
14、 point is reflected throughout the system by a change in frequency.Because there are many generators supplying power into the system,some means must be provided to allocateSection 3 Operation and Control of Power SystemsThe control measures of power and frequency include:（1）Regulation of the generat
15、ors speed governor（2）Underfrequency load shedding（3）Automatic generation control(AGC)AGC is an effective means for power and frequency control in large-scale power systems.In an interconnected power system,the primary objectives of AGC are to regulate frequency to the specified nominal value and to
16、maintain the interchange power between control areas at theSection 3 Operation and Control of Power SystemsAGC.The integral control action ensures zero frequency error in the steady state.The supplementary generation control action is much slower than the primary speed control action.As such it take
17、s effect after the primary speed control(which acts on all units on regulation)has stabilized the system frequency.Thus,AGC adjusts load reference settings of selected units,and hence their output power,to override the effects of the composite frequency regulation characteristics of the power system
18、.In so doing,it restores theSection 3 Operation and Control of Power Systems generation of all other units not on AGC to scheduled values.Reactive power and voltage control For efficient and reliable operation of power systems,the control of voltage and reactive power should satisfy the following ob
19、jectives:（1）Voltages at the terminals of all equipment in the system are within acceptable limits.Both utility equipment and customer equipment are designed to operate at a certain voltage rating.Prolonged operation of the equipment at voltages outside theSection 3 Operation and Control of Power Sys
20、temsThe problem of maintaining voltages within the required limits is complicated by the fact that the power system supplies power to a vast number of loads and is fed from many generating units.As loads vary,the reactive power requirements of the transmission system vary.Since reactive power can no
21、t transmitted over long distances,voltage control has to be effected by using special devices dispersed throughout the system.This is in contrast to the control of frequency which depends on the overall system active power balance.The proper selection and coordination of equipment forSection 3 Opera
22、tion and Control of Power Systemscontrolling reactive power and voltage are among the major challenges of power system engineering.The control of voltage levels is accomplished by controlling the production,absorption,and flow of reactive power at all levels in the system.The generating units provid
23、e the basic means of voltage control;the automatic voltage regulators control field excitation to maintain a scheduled voltage level at the terminals of the generators.Additional means are usually required to control voltage throughout the system.The devices used for this purpose may be classified a
24、s follows:Section 3 Operation and Control of Power Systems（1）Sources or sinks of reactive power,such as shunt capacitors,shunt reactors,synchro-nous condensers,and static var compensators(SVCs).（2）Line reactance compensators,such as series capacitors.（3）Regulating transformers,such as tap-changing t
25、ransformers and boosters.Shunt capacitors and reactors,and series capacitors provide passive compensation.They are either permanently connected to the transmission and distribution system,or switched.They contribute toSection 3 Operation and Control of Power Systemsvoltage control by modifying the n
26、etwork characteristics.Synchronous condensers and SVCs provide active compensation,the reactive power absorbed/supplied by them is automatically adjusted so as to maintain voltages of the buses to which they are connected.Together with the generating units,they establish voltages at specific points
27、in the system.Voltages at other locations in the system are determined by active and reactive power flows through various circuit elements,including the passive compensating devices.ReturnNew Words and Expressionsreliablea.可靠的busn.母线overloadn.过载，超载，过负荷optimala.优化的，最优的，最佳的production cost 生产成本，生产费用hyd
28、ro-generationn.水力发电dry period 枯水期replenishmentn.（再）补充，充实，充满New Words and Expressionsmagnetizing current激磁电流，励磁电流electric clock电钟active power balance 有功功率平衡supplementary control 辅助控制load-frequency control(LFC)负荷频率控制speed governor 调速器underfrequency load shedding低周减载，低频减负荷automatic generation control(A
29、GC)自动发电控制 New Words and Expressionsstabilizev.使稳定reactive power无功功率active power有功功率automatic voltage regulator 自动电压调节器shunt capacitor 并联电容器，并联电容shunt reactor并联电抗器，并联电抗synchronous condenser同步调相机static var compensators(SVCs)静止无功补偿器New Words and Expressionsseries capacitor 串联电容器tap-changing transformer
30、可调分接头变压器boostern.升压器，增压器，加压泵 ReturnTranslation of Numeral Words1.1.句型：句型：as+as+形容词形容词+as +as 数词数词+as high as可译成“高达”；as heavy as可译成“重达”；as large as可译成“大到（至）”；as low as可译成“低到（至）”；as many as可译成“多到”。(1)The temperature at the suns center is as high as 10000000C.太阳中心的温度高达摄氏1000万度。(2)The outer portion of t
31、he wheel may travel as fast as 600 miles per hour.轮子外缘的运动速度可能高达每小时六百英里。Translation of Numeral Words2.2.数量增加的翻译数量增加的翻译（1）句型：“be n times as+形容词（或副词）+as”，“be n times+比较级+than”，“be+比较级+than+名词+by n times”，“be+比较级+by a factor of n”，可译成“是的n倍”、“n倍于”或“比大（n-1）倍”。1)The new machine turns three times as fast as
32、 the old one.新机器的转速是旧机器的三倍。（或译成：新机器的转速比旧机器快两倍。）Translation of Numeral Words2.2.数量增加的翻译数量增加的翻译（2）句型：“as+形容词或副词+again as”，“again as+形容词或副词+as”，可译成“是的两倍”，或“比多（大，长）一倍”。如果again前加half，则表示“是的1.5倍”或“比多（大，长）半倍”。1)This wire is as long again as that one.这根金属线的长度是那根的2倍。Translation of Numeral Words2.2.数量增加的翻译数量增
33、加的翻译2)The amount left was estimated to be again as much as all the zinc that has been mined.当时估计，剩余的锌储量是已开采量的两倍。3)The resistance of aluminum is approximately half again as great as that of copper for the same dimensions.尺寸相同时，铝的电阻约为铜的一倍半。Translation of Numeral Words2.2.数量增加的翻译数量增加的翻译（3）用带有“增大”意思的动词（
34、increase,rise,grow等）和含有数词的词语配合。句型有：“动词+n times”，“动词+by+n times”，“动词+to+n times”，“动词+n-fold”，“动词+by a factor of+n”，可译成“增加到n倍”，“增加了（n-1）倍”；“（by）n+单位（或n%）”表示净增量，数词可照译。1)The production has increased three times.生产增加了两倍。Translation of Numeral Words2.2.数量增加的翻译数量增加的翻译2)The strength of the attraction increa
35、ses by four times if the distance between the original charges is behalved.如果原电荷的距离缩短一半，则引力就增大到原来的4倍。3)This year,the production of this kind of machine in our plant is estimated to increase to 3 times compared with 1980.今年我厂这种机器的产量预计比1980年增长2倍。Translation of Numeral Words2.2.数量增加的翻译数量增加的翻译4)Since th
36、e first transatlantic telephone cable was laid the annual total of telephone calls between UK and Canada has increased sevenfold.自从第一条横跨大西洋的电话电缆敷设以来，英国与加拿大之间的年通话量增加了六倍。5)If X is doubled,Y is increased by a factor of 4.若X增加到两倍，则Y增加到四倍。6)Automation will help us to raise the output of production by thi
37、rty percent.自动化能帮助我们提高产量30%。Translation of Numeral Words2.2.数量增加的翻译数量增加的翻译（4）用表示倍数的动词表示的量的增加。例如，double可译成“增加一倍”，“翻一番”，“是二倍”；treble 可译成“增加两倍”，“增加到三倍”；quadruple可译成“增加三倍”，“翻两番”。1)As the high voltage was abruptly trebled all the values burnt.由于高压突然增加了两倍，管子都烧坏了。2)The new airport will double the capacity
38、of the existing one.新机场是现有机场容量的2倍。ReturnExercises I.Choose the best answer into the blank 1.The objective of the optimal economic operation of power systems is .A.to minimize the total production cost B.to maintain frequency constant C.to maintain voltages constant D.to ensure balance between genera
39、tion and load Exercises I.Choose the best answer into the blank 2.The frequency of a power system is determined mainly by .A.bus voltages B.active power generation C.reactive power generation D.active power generation and consumption3.The voltage levels at the terminals of generators are controlled
40、mainly by .A.static var compensatorsB.series capacitors C.automatic voltage regulatorsD.shunt reactorsExercises I.Choose the best answer into the blank 4.When the system frequency is changed away from the rating,must be regulated.A.system voltagesB.reactive power C.active powerD.generators excitatio
41、n 5.Regulation of the generators speed governor can change its output.A.reactive powerB.active power C.terminal voltageD.reactive current Exercises II.Answer the following questions according to the text 1.What parts are included in the total cost of operation?2.In an interconnected power system,wha
42、t is the main function of an AGC system?3.What measures can be used for voltage control in a power system?4.Why is the problem of maintaining voltages within the required limits complicated?5.How does the active power loss of a power system vary as the reactive power flow decreases?Exercises III.Tra
43、nslate the following into Chinese When two or more synchronous machines are interconnected,the stator voltages and currents of all the machines must have the same frequency and the rotor mechanical speed of each is synchronized to this frequency.Therefore,the rotors of all interconnected machines mu
44、st be in synchronism.In a generator,the electromagnetic torque opposes rotation of the rotor,so that mechanical torque must be applied by the prime mover to sustain rotation.The electrical torque (or power)output of theExercises III.Translate the following into Chinese generator is changed only by c
45、hanging the mechanical torque input by the prime mover.The effect of increasing the mechanical torque input is to advance the rotor to a new position relative to the revolving magnetic field of the stator.Conversely,a reduction of mechanical torque or power input will retard the rotor position.In a synchronous motor,the roles of electrical and mechanical torques are reversed compared to those in a generator.ReturnChapter 6Section 3 End