电气工程专业英语课件

1、1,各位老师： 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 Power Bus voltage will change according to load flow variation, whereas they are mainly affected by

2、 production and absorption of reactive power at those buses. Synchronous generators can generate or absorb 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 reacti

3、ve power is, however, 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 impedance) load, the lines produce net reactive power; at loads abo

4、ve the natural load, the lines absorb reactive power. Underground cables, owing to their high capacitance, have high natural loads. They are always loaded below their natural loads, and hence generate reactive power under all operating conditions. Transformers always absorb reactive power regardless

5、 of their loading; at no load, the shunt magnetizing 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 composed of a large number of devices. The compo

6、sition 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 and reactive power of the composite loads vary as a function of voltage magnitudes. Loads at low-lagging power factors cause

7、excessive voltage drops in the transmission network and are uneconomical to supply. Industrial 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

8、y or absorb reactive power and thereby control the reactive power balance in a desired manner,5,Lecture 9,New Words and Expressions compensation 补偿 absorption 吸收 excitation 励磁 field current 励磁电流 end-region 端部 armature 电枢 surge impedance 波阻抗 natural load 自然负荷 leakage 漏电 lagging 滞后 incentive 动机,6,Lect

9、ure 9,Part2 Objectives and Methods of Voltage Regulation For efficient and reliable operation of power systems, the control of voltage and reactive power should satisfy the following objectives: i) Voltages at the terminals of all equipment in the system are within acceptable limits. Both utility eq

10、uipment and customers equipment are designed to operate at a 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 maximize utilization of the tr

11、ansmission 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 minimized so as to reduce and losses to a practical minimum. This ensures that the transmission system operates effici

12、ently, i. e. , mainly for active power transfer. The 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 trans

13、mission 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 devices dispersed throughout the system. This is in contrast to the control of

14、 frequency which depends on the,8,Lecture 9,overall system active power balance. The proper selection and coordination of equipment for controlling reactive power and voltage are among the major challenges of power system engineering. The control of voltage levels is accomplished by controlling the

15、production, absorption, and flow of reactive power 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 generators. Additional means

16、 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 capacitors, shunt reactors, synchronous condensers, and static var,9,Lecture 9,compensators (SVCs). ii) Line reactance com

17、pensators, such as series capacitors. iii) Regulating transformers, such as 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 switched. They

18、contribute to voltage control by modifying the network 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 generatin

19、g units, they establish voltages at specific points in the system,10,Lecture 9,Voltages at other locations in the 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 r

20、equired 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. 维持电压在所要求的限定范围内是比较复杂的，这是因为 电力系统给数目众多的负载供电，而且又从发电机组得到 电能,11,Lecture 9,2. The proper selection and coordination of equipment for controlling reactive power and

21、 voltage are among the major challenges of power system engineering. 无功和电压控制装置的合理选择与配合是电力系统工程所面 临的主要挑战之一。 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 buses to which they are c

22、onnected. 同步调相机和SVC提供有源补偿；它们吸收/提供的无功功率 都会自动调节，以维持与之相连的母线的电压,12,Lecture 9,Part 3 Comparative Summary of Alternative Forms of Compensation There are several methods and various devices to realize reactive power compensation. Comparative summary of alternative forms of compensation is as followed. i) S

23、witched shunt capacitor compensation 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 the effective line angle is the primary con

24、sideration. ii) Series capacitors compensation is self-regulating, i. e. , its reactive power output increases with line loading. It is ideally suited for applications where reduction of the effective line angle,13,Lecture 9,is the primary consideration. It increases the effective natural load as we

25、ll as the small-signal stability and to obtain the desired load division among parallel 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

26、. 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 of such an application is a long line requiring compensation, which causes the phase

27、angle across the line to take a desired value so as not to adversely affect loading patterns on parallel lines,14,Lecture 9,iv) Synchronous 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 m

28、ade to either generate or absorb reactive power. With 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 compensators have several advantages ove

29、r static compensators. Synchronous compensators contribute to system short-circuit capacity. Their reactive power production is not affected by the system voltage. During power swings (electromechanical oscillations) there is an exchange of kinetic energy between a synchronous condenser and the powe

30、r system. During such power swings, a synchronous condenser can supply,15,Lecture 9,a large amount of reactive 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

31、 is better able to cope 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 application requiring direct and rapid control of voltage. It has a dist

32、inct advantage over series capacitors where compensation is required to prevent voltage sag at a bus involving multiple lines. Since shunt compensation 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 seri

33、es compensation of each of the lines,16,Lecture 9,When an SVS is used to 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 offers no

34、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 the SVS is sized. The ratings of the SVS should be based on very thorough studies which

35、define its total Mvar and the switched and dynamically controlled portions. An SVS has limited overload capability and has higher than series capacitor compensation,17,Lecture 8,1. It is ideally suited for compensating transmission lines if reduction of the effective characteristic impedance, rather

36、 than reduction of the effective line angle is the primary consideration. 它理想地适合于输电线补偿，如果首要考虑因素是有效特性 阻抗的减小而不是有效线路角度的减小。 2. When an SVS is used to permit a high power transfer over a long distance, the possibility of instability when the SVS is pushed to its limit must be recognized. 当SVS用于支持长距离大功率输电

37、时，必须意识到将SVS推向 其极限时失稳的可能性,18,Lecture 9,New Words and Expressions utility 电力单位 prolonged 延长的，长时期的 adversely 反过来 dispersed 分散的 sink 接收器 synchronous condenser 同步调相机 alternative forms 不同形式 self-regulating 自调的 sunsynchronous 次同步的 swing 摇摆 cope with 应对，与 竞争 voltage sag 电压暂降 thorough 十分的，彻底的 deenergized 失磁的

38、，不带电的 prescribed 指定的,19,Lecture 9,ABBREVIATIONS (ABBR.) 1. AVR Automatic Voltage Regulator 自动电压调节器 2. SVC Static Var Compensator 静止无功补偿器 3. SVS Static Var System 静止无功系统 4. STATCOM Static Synchronous Compensator 静止同步补偿器 5. ULTC Under-Load-Tap-Changing 有载调分接头,20,Lecture 9,SUMMARY OF GLOSSARY 1. 励磁状况 e

39、xcitation status overexcited 过励磁的 underexcited 欠励磁的 2. 负荷状况 load status no load 空载 full load 满载 rated load 额定负载 3. 无功补偿 reactive power compensation passive compensation 无源补偿 active compensation 有源补偿 4. 无功补偿器 reactive power compensators synchronous compensator 同步补偿器 static compensator 静止补偿器,21,Lectur

40、e 8,1.3 Test-Running and Commissioning Stage Scene 1: Pre-start-up Check (Fu 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 water system, generator

41、 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 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 condensat

42、e pump is ready for start-up. K: OK. Please check the condensate system 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 deaerator is suitable. K

43、: 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. The feedwater system is checked normal. K: Now vacuate the condenser, and power the ejector,Lecture 8,23,F: The ejector is sta

44、rted. The condenser is vacuated gradually. K: I see. Heat up the deaerators, and control 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? K: OK. S

45、tart 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 reporting to Kong Er) F: The overall check before ignition has been finished. K: Okay. F: Can we start the vibrato

46、rs and the heaters of the electrostatic precipitator now? K: Sure. What is the temperature 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: Okay. Put the TV monitor in

47、to operation, start up the induced-draft fans and the forced-draft fans in sequence,25,F: Yes. K: Adjust the boiler air flow and the combustion chamber draft, now begin to ignite. F: Yes, sir! Scene 3: Synchronization (In front of the generator control panel) F: The electrical test is completed. No

48、abnormal alarm signal is found. K: OK. Prepare synchronize. F: Yes. Raise generating voltage to rated value, check the voltage between phases in balance. Get ready for synchronizing. I will push the start-up button of the automatic synchronizer,Lecture 8,26,K: OK. The generator is in connection to t

49、he grid. The light is on. Synchronization is successfully completed. F: The unit takes in the load. Ah, the inlet air for generator and exciter is over temperature. K: Check the hydrogen cooler right now. Adjust the temperature to be at 40. Control the temperature of the cooling water for the genera

50、tor stator at about 47 at the inlet. Increase the pressure of hydrogen up to 0.4 MPa gradually. Pay attention to the seal oil system. F: Yes. The condition of the boiler is stable and all the parameters are within their limits,Lecture 8,27,K: Now, the low load warm-up starts. Put the high pressure h

51、eaters into operation in sequence. The temperature of the main steam and the reheat steam can not be over 540 . F: Yes. K: Turn on the primary air fans. Get ready to operate the milling system. F: Yes, sir. The entire milling system has been checked normal, oil burners look proper, and adequate coals are in the coal bunkers. K: Okay. Turn on No.1 coal mill. F: No. 1 pulverizer is overcurrent. The protection operated and the breaker tripped. Two alarm windows of “No. 1 pulverizer trip,Lecture 8,28,and “10 kV A bus earth” are lighted. K: Go and make a check-up in the switch