電氣工程專業(yè)英語(yǔ)課件lecture9-2012

1、1,各位老師： 上午好！,Lecture 9,Specialized English for Electrical Engineering,2,Lecture 9,Reading and Translation Voltage Regulation and Reactive Power Compensation Part 1 Production and Absorption of Reactive

2、 Power Bus voltage will change according to load flow variation, whereas they are mainly affected by production and absorption of reactive power at those buses. Synchronous generators can generate or abso

3、rb reactive power depending on the excitation. When overexcited they supply reactive power, and when underexcited they absorb reactive power. The capability to continuously supply or absorb reactive power is, however

4、, limited by the filed current, armature current, and end-region heating limits.,3,Lecture 9,Overhead lines, depending on the load current, either absorb or supply reactive power. At loads below the natural (surge imped

5、ance) load, the lines produce net reactive power; at loads above the natural load, the lines absorb reactive power. Underground cables, owing to their high capacitance, have high natural loads. They are alw

6、ays loaded below their natural loads, and hence generate reactive power under all operating conditions. Transformers always absorb reactive power regardless of their loading; at no load, the shunt magnetizi

7、ng reactance effects predominate; and at full load, the series leakage inductance effects predominate. Loads normally absorb reactive power. A typical load bus,4,Lecture 9,supplied by a power system is com

8、posed of a large number of devices. The composition changes depending on the day, season, and weather conditions. The composite characteristics are normally such that a load bus absorbs reactive power. Both active power

9、and reactive power of the composite loads vary as a function of voltage magnitudes. Loads at low-lagging power factors cause excessive voltage drops in the transmission network and are uneconomical to supply. Industrial

10、 consumers are normally charged for reactive as well as active power; this gives them an incentive to improve the load power factor by using shunt capacitors. Compensating devices are usually added to suppl

11、y or absorb reactive power and thereby control the reactive power balance in a desired manner.,5,Lecture 9,New Words and Expressions compensation 補(bǔ)償 absorption 吸收 excitation 勵(lì)磁

12、 field current 勵(lì)磁電流 end-region 端部 armature 電樞 surge impedance 波阻抗 natural load 自然負(fù)荷 leakage 漏電

13、 lagging 滯后 incentive 動(dòng)機(jī),6,Lecture 9,Part2 Objectives and Methods of Voltage Regulation For efficient and reliable operation of power systems, the control of voltage and reactive pow

14、er should satisfy the following objectives: i) Voltages at the terminals of all equipment in the system are within acceptable limits. Both utility equipment and customers equipment are designed to operate at a

15、 certain voltage rating. Prolonged operation of the equipment at voltage outside the allowable range could adversely affect their performance and possibly cause them damage. ii) System stability is enhanced to

16、 maximize utilization of the transmission system. As described in some academic papers, voltage and reactive power control have a significant impact on system stability.,7,Lecture 9,iii) The reactive power flow is minimi

17、zed so as to reduce and losses to a practical minimum. This ensures that the transmission system operates efficiently, i. e. , mainly for active power transfer. The problem of maintaining voltages wi

18、thin 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

19、 system vary. This is abundantly clear from the performance characteristics of transmission lines. Since reactive power cannot be transmitted over long distances, voltage control has to be effected by using special devic

20、es dispersed throughout the system. This is in contrast to the control of frequency which depends on the,8,Lecture 9,overall system active power balance. The proper selection and coordination of equipment for controlling

21、 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

22、at all levels in the system. The generating units provide the basic means of voltage control; the automatic voltage regulators (AVRs) control field excitation to maintain a scheduled voltage level at the terminals of the

23、 generators. Additional means are usually required to control voltage throughout the system. The devices used for this purpose may be classified as follows: i) Sources or sinks reactive power, such as shunt ca

24、pacitors, shunt reactors, synchronous condensers, and static var,9,Lecture 9,compensators (SVCs). ii) Line reactance compensators, such as series capacitors. iii) Regulating transformers, such as

25、tap-changing transformers and boosters. Shunt capacitors and reactors, and series capacitors provide passive compensation. They are either permanently connected to the transmission and distribution system, or

26、 switched. They contribute to voltage control by modifying the network characteristics. Synchronous condensers and SVCs provide active compensation; the reactive power absorbed/supplied by them is automatical

27、ly 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 in the system.,10,Lecture 9,Voltages at other locations in t

28、he system are determined by active and reactive power flows through various circuit elements, including the passive compensating devices. 1. The problem of maintaining voltages within the required limits i

29、s complicated by the fact that the power system supplies power to a vast number of loads and is fed from many generating units. 維持電壓在所要求的限定范圍內(nèi)是比較復(fù)雜的，這是因?yàn)?電力系統(tǒng)給數(shù)目眾多的負(fù)載供電，而且又從發(fā)電機(jī)組得到 電能。

30、,11,Lecture 9,2. The proper selection and coordination of equipment for controlling reactive power and voltage are among the major challenges of power system engineering. 無功和電壓控制裝置的合理選擇與配合是電

31、力系統(tǒng)工程所面 臨的主要挑戰(zhàn)之一。 3. Synchronous condensers and SVCs provide active compensation; the reactive power absorbed/supplied by them is automatically adjusted so as to maintain voltages of the

32、 buses to which they are connected. 同步調(diào)相機(jī)和SVC提供有源補(bǔ)償；它們吸收/提供的無功功率 都會(huì)自動(dòng)調(diào)節(jié)，以維持與之相連的母線的電壓。,12,Lecture 9,Part 3 Comparative Summary of Alternative Forms of Compensation

33、 There are several methods and various devices to realize reactive power compensation. Comparative summary of alternative forms of compensation is as followed. i) Switched shunt capacitor compensation

34、 generally provides the most economical reactive power source for voltage control. It is ideally suited for compensating transmission lines if reduction of the effective characteristic impedance, rather than reduction of

35、 the effective line angle is the primary consideration. ii) Series capacitors compensation is self-regulating, i. e. , its reactive power output increases with line loading. It is ideally suited for applicatio

36、ns where reduction of the effective line angle,13,Lecture 9,is the primary consideration. It increases the effective natural load as well as the small-signal stability and to obtain the desired load division among parall

37、el lines. Series capacitor compensation could cause subsynchronous resonance problems requiring special solution measures. In addition, protection of lines with series and shunt capacitors requires special attention.

38、 iii) A combination of series and shunt capacitors may provide the ideal form of compensation in some cases. This allows independent control of the effective characteristic impedance and the load angle. An example

39、of such an application is a long line requiring compensation, which causes the phase angle across the line to take a desired value so as not to adversely affect loading patterns on parallel lines.,14,Lecture 9,iv) Synchr

40、onous Condenser: A synchronous condenser is a synchronous machine running without a prime mover or a mechanical load. By controlling the field excitation, it can be made to either generate or absorb reactive power. With

41、a voltage regulator, it can automatically adjust the reactive power output to maintain constant terminal voltage. It draws a small amount of active power from the power system to supply losses. Synchronous com

42、pensators have several advantages over static compensators. Synchronous compensators contribute to system short-circuit capacity. Their reactive power production is not affected by the system voltage. During power swings

43、 (electromechanical oscillations) there is an exchange of kinetic energy between a synchronous condenser and the power system. During such power swings, a synchronous condenser can supply,15,Lecture 9,a large amount of r

44、eactive power, perhaps twice its continuous rating. It has about 10% to 20% overload capability for up to 30 minutes. Unlike other forms of shunt compensation, it has an internal voltage source and is better able to cope

45、 with low system voltage conditions. Some combustion turbine peaking units can be operated as synchronous condensers if required. V) A static var system (SVS) such as SVC and STATCOM is ideally suited for appl

46、ication requiring direct and rapid control of voltage. It has a distinct advantage over series capacitors where compensation is required to prevent voltage sag at a bus involving multiple lines. Since shunt compensation

47、is connected to the bus and not to particular lines, the total cost of the regulated shunt compensation may be substantially less than that for series compensation of each of the lines.,16,Lecture 9,When an SVS is used t

48、o permit a high power transfer over a long distance, the possibility of instability when the SVS is pushed to its limit must be recognized. When operating at its capacitive limit, the SVS becomes a simple capacitor; it o

49、ffers no voltage control and its reactive power drops with the square of the voltage. Systems heavily dependent on shunt compensation may experience nearly instantaneous collapse when loadings exceed the levels for which

50、 the SVS is sized. The ratings of the SVS should be based on very thorough studies which define its total Mvar and the switched and dynamically controlled portions. An SVS has limited overload capability and has higher t

51、han series capacitor compensation.,17,Lecture 8,1. It is ideally suited for compensating transmission lines if reduction of the effective characteristic impedance, rather than reduction of the effective lin

52、e angle is the primary consideration. 它理想地適合于輸電線補(bǔ)償，如果首要考慮因素是有效特性 阻抗的減小而不是有效線路角度的減小。 2. When an SVS is used to permit a high power transfer over a long distance, the possibility of instability when

53、 the SVS is pushed to its limit must be recognized. 當(dāng)SVS用于支持長(zhǎng)距離大功率輸電時(shí)，必須意識(shí)到將SVS推向 其極限時(shí)失穩(wěn)的可能性。,18,Lecture 9,New Words and Expressions utility 電力單位 prolonged 延長(zhǎng)的，長(zhǎng)時(shí)期的 adv

54、ersely 反過來 dispersed 分散的 sink 接收器 synchronous condenser 同步調(diào)相機(jī) alternative forms 不同形式 self-regulating 自調(diào)的 sunsynchronous 次同步的 swing 搖擺

55、 cope with 應(yīng)對(duì)，與… 競(jìng)爭(zhēng) voltage sag 電壓暫降 thorough 十分的，徹底的 deenergized 失磁的，不帶電的 prescribed 指定的,19,Lecture 9,ABBREVIATIONS (ABBR.) 1. AVR Automatic Voltage Regulator 自動(dòng)電壓調(diào)節(jié)器 2.

56、SVC Static Var Compensator 靜止無功補(bǔ)償器 3. SVS Static Var System 靜止無功系統(tǒng) 4. STATCOM Static Synchronous Compensator

57、 靜止同步補(bǔ)償器 5. ULTC Under-Load-Tap-Changing 有載調(diào)分接頭,20,Lecture 9,SUMMARY OF GLOSSARY 1. 勵(lì)磁狀況 excitation status overexcited

58、 過勵(lì)磁的 underexcited 欠勵(lì)磁的 2. 負(fù)荷狀況 load status no load 空載 full load 滿載 rate

59、d load 額定負(fù)載 3. 無功補(bǔ)償 reactive power compensation passive compensation 無源補(bǔ)償 active compensation 有源補(bǔ)償 4. 無功補(bǔ)償器 reactive power c

60、ompensators synchronous compensator 同步補(bǔ)償器 static compensator 靜止補(bǔ)償器,21,Lecture 8,1.3 Test-Running and Commissioning Stage Scene 1: Pre-start-up Check (F

61、u Yu goes into the central control room, spanner in his hand) K: How is the condition of the start-up, Xiao Fu? F: Shift Supervisor, the circulating water system, auxiliary steam system, closed cooling

62、water system, generator cooling system, seal oil system, hydrogen gas system, the lubricating oil system and the jigger have been checked normal and put into operation already. Other systems

63、 are also in order. The water has been injected into the 1500 t condensate tank. K: I see. Is there anything else?,22,F: The condensate pump is ready for start-up.K: OK. Please check the condensate system

64、carefully after start-up.F: Yes. … The condensate system is in regular operation. The condenser back washing is being done. … The Chemical staffs informed that the water is qualified. The water level in the

65、 deaerator is suitable.K: Check the motor-driven feedwater pump and the feedwater system carefully, prepare to start the motor-driven feedwater pump.F: Yes! …The motor-driven feedwater pump is run. T

66、he feedwater system is checked normal.K: Now vacuate the condenser, and power the ejector.,Lecture 8,23,F: The ejector is started. The condenser is vacuated gradually.K: I see. Heat up the deaerators, and control

67、the feedwater temperature below 104℃. Inject water into drum.F: Water level in drum is suitable, but the boiler water is unqualified. Discharge the water and inject fresh water simultaneously, is it OK

68、?K: OK. Start one EHV oil pump. Check the oil pressure. Ignite the boiler when the water is qualified.F: Yes, sir!,Lecture 8,24,Lecture 8,Scene 2: Ignition (In the central control room, Fu Yu is repor

69、ting to Kong Er) F: The overall check before ignition has been finished. K: Okay. F: Can we start the vibrators and the heaters of the electrostatic precipitator now? K: Sure. What is the tempera

70、ture of the heavy oil? Check the light oil ignitors and the heavy oil burners. F: Now the temperature of the fuel oil is 118℃. It meets the requirement of ignition. Start igniting, OK? K: Oka