外文翻譯--大型發(fā)電機干擾下發(fā)電機保護的性能

1、<p>　　English Material:</p><p>　　Performance of Generator Protection During Major System Disturbance</p><p><b>　　Abstract：</b></p><p>　　Disturbance is an inher

2、ent part of easy power system during the transition from one steady-state operating condition to the next. Protective relays may experience abnormal operating conditions during this transient period. This paper reviews c

3、ontrol actions drat play a part during the transition and provides technical guidance to the industry on the application and setting of generator protective relays that can operate during major system disturbances. </

4、p><p>　　Index Terms：</p><p>　　AC generator excitation、ac generator protection、 governors、power system control turbines.</p><p>　?、?INTRODUCTION：</p><p>　　Every power syste

5、m is subject from time to time to transient disturbances primarily due to faults and/or switching of major load. Normally, the system adapts to a new steady-state condition with the help of generator excitation and turbi

6、ne governor control systems. A variety of additional power system control schemes may also be used to help restore an acceptable new steady-state condition.</p><p>　　One of the lessons learned from the past

7、major disturbances is that some of the functions associated with generator protection may operate during these transient conditions. It is important for the relays to provide protection while optimizing their coordinatio

8、n to avoid undesirable operation during the system disturbances and thereby help preserve the integrity of the power grid.</p><p>　　Brief descriptions of past power system disturbances as well as generator e

9、xcitation, turbine governor, and power system controls are included in this paper. The balance of the paper discusses the generator protection functions that may operate during system disturbances.</p><p>　　

10、Ⅱ. POWER SYSTEM DISTURBANCES：</p><p>　　Power system disturbances are events that produce abnormal system conditions and the state of the system may change from normal to emergency. These disturbances can be

11、classified into two groups-small and large. Large disturbances are a challenging problem for the utilities because of the size and complexity of the power system. Adequate protection and control actions are required afte

12、r a system disturbance to prevent further degradation of the system and restoration to the normal state.</p><p>　　Many system disturbances can be attributed to tight operating margins and less redundancy in

13、generation, transmission, and distribution capability. These are best addressed at the planning stage. A properly designed system is less vulnerable to large-scale disturbances. However, small disturbances cannot be elim

14、inated due to the physical nature of the system. Overhead lines constitute a significant component of any power system and experience frequent faults that are caused by variety of reasons</p><p>　　Stable ope

15、ration of a power system requires a continuous matching between energy supply to the prime movers and the electrical load on the system and an adequate reactive power support mechanism to maintain voltage within limits a

16、t different buses. These conditions are not satisfied during faults and other disturbances. During a fault, the terminal voltage dips and power transfer through the faulted system are altered depending on, the type of fa

17、ult. After successful clearing of the fault, the s</p><p>　　Even the successful clearing of faults may sometimes lead to undesired relay operations because of line overloads, inadequate reactive power suppor

18、t, and an improper relay setting. These may, in turn, develop into large system disturbances due to cascading. Disoperation of relays may result in undesired and/or sympathy tripping leading to large system disturbances.

19、 Inadequate protection arrangements, such as the absence of bus-bar protection for critical system buses, may also result in system d</p><p>　　Performance of the generator excitation system and the turbine c

20、ontrol system are important during a system disturbance. Coordination between these systems, system protection, and other control strategies are necessary to avoid system collapse. Transient and dynamic stability studies

21、 should be periodically conducted in order to develop adequate control and protection strategies.</p><p>　　A. Excitation Control：</p><p>　　The excitation system of a generator provides the energ

22、y for the magnetic field that keeps the generator in synchronism with the power system. In addition to maintaining the synchronism of the generator, the excitation system also affects the amount of reactive power that th

23、e generator may absorb or produce. If the terminal voltage is fixed, increasing the excitation power will increase the synchronizing torque of the machine and increase the reactive power output. Decreasing the excitation

24、 powe</p><p>　　'There are a variety of control functions that can be applied to the excitation system, including automatic voltage regulation (AVR), constant power factor regulation, and constant reactiv

25、e power regulation. The excitation system may also operate in manual control with no automatic regulation. All of the automatic control modes may have supplementary controls. These supplementary controls may ensure that

26、even under automatic regulation of a primary parameter, the generator is always operated wit</p><p>　　1、maximum and/or minimum excitation level limits (OEL/MEL respectively, these limits may be tithe de

27、pendent);</p><p>　　2、stator current limit to prevent stator thermal overload;</p><p>　　3、volts per hertz limit to prevent equipment damage due to excessive flux levels;</p><p>　　4、t

28、erminal voltage limit to prevent equipment damage due to excessive dielectric stress;</p><p>　　5、line drop compensation to increase generator response to system voltage depressions;</p><p>　　6、r

29、eactive power sharing controls for generators trying to regulate the same parameter;</p><p>　　7、power system stabilizer to damp low-frequency oscillations;</p><p>　　8、under excited limit (UEL) t

30、o protect against generator stator end-winding treating while operating in the under excited mode [15].</p><p>　　The most commonly used control mode for generators of significant size that are connected to a

31、 power system is the AVR mode. In this mode, the excitation system helps to maintain power system voltage within acceptable limits by supplying or absorbing reactive power as required and also helps maintain synchronism

32、of the generator with the power system by increasing synchronizing torque when required.</p><p>　　In stable steady state operation, a power system has an exact match of mechanical power delivered to generato

33、rs and electrical power consumed by loads. Further; the voltage is regulated within narrow limits. Small disturbances resulting in. power or voltage oscillations are quickly damped. Frequency is maintained within accepta

34、ble limits by turbine governor controls and sometimes by system load control as noted in other sections of this paper. During Large disturbances, excitation controls act t</p><p>　　Large system disturbances

35、are typically caused by short circuits of different types. The opening of appropriate high-speed breakers isolates the fault. During the fault, the terminal voltage dips and, in response, the exciter increases its output

36、 voltage to ceiling which causes the excitation current into the field to increase at a rate determined by the voltage divided by the inductance of the field.</p><p>　　System disturbances are also caused whe

37、n a generation unit is suddenly dropped or when a breaker is suddenly opened and a load is dropped. When a unit is dropped, other nearby units pick up the load of the dropped unit and in response to the drop in mercurial

38、 voltage, the excitation of each of these units will increase When a breaker is suddenly opened and a load is dropped, the excitation will be reduced.</p><p>　　The electrical powertransferred from the genera

39、tor, an electric machine, to the load is given by the equation</p><p><b>　　(A1.1)</b></p><p><b>　　where</b></p><p>　　internal voltage and is proportional to

40、the excitation current;</p><p>　　load voltage;</p><p>　　reactance between the generator and the load;</p><p>　　delta, the angle that the internal voltage leads the load voltage.<

41、/p><p><b>　　(A1.2)</b></p><p><b>　　where</b></p><p>　　mechanical turbine power of the generating unit;</p><p>　　electromagnetic power out of the ge

42、nerating unit;</p><p>　　accelerating power.</p><p>　　The mechanical power is provided by the turbine and the average mechanical power must be equal to the average electrical power. When a system

43、 disturbance occurs, there is a change in one of the parameters of the electrical power equation. For faults, typically, the reactance between the generator and the load()，the load voltage()，or some combination of these

44、two parameters causes the electrical power to change. For example, for a short circuit, the load voltage is reduced; for a breaker opening,</p><p>　　In both cases, the instantaneous mechanical power provided

45、 by the turbine is no longer equal to the instantaneous electrical power delivered or required by the load. This difference must be accounted for.</p><p>　　For a short time after a disturbance, the turbine c

46、ontrol will not have much affect on the turbine power and the rotor will either absorb or provide the required transient energy. In the case of a fault, the energy absorbed by the rotor increases its angular velocity. Wh

47、en the Load on a unit is suddenly increased, the energy furnished by the rotor results in a decrease in the rotor angular velocity. The exciter will respond to these disturbances based on terminal voltage measured.</p

48、><p>　　To understand what is happening, let us consider the example of a three-phase solid fault at the load. The load voltage shorted (), and the reactance between the generate and the load () is unchanged. Fr

49、om (1), the electrical power during the fault is zero. Since the turbine control cannot it extraneously reduce its power output, the power that was previously input to the load now accelerates the combine rotating mass o

50、f both the generator and turbine rotors [see (2)] This causes angle delta to </p><p>　　In disturbances where short circuits depress the system voltage, prevail electrical power cannot fully be delivered thro

51、ugh the transmission system. Transient stability become a threat to the power system within a time frame of less than 1 s. During the short circuit, the generator rotor accelerate due to mismatch of the reduced electrica

52、l power output with the constant mechanical power input (in the transient time frame before the turbine governor control can react). Fast response of the AVR an</p><p>　　In extended disturbances beyond the t

53、ransient stability time frame, the AVR again Lies to regulate voltage, but in this case it will attempt to steadily increase or reduce excitation to regulate voltage. Periodic oscillations are not evident as in the case

54、of challenges to transient stability and the system stress may persist for periods of up to tens of seconds or even longer. Prolonged low voltages may result from loss of important transmission capability or loss of impo

55、rtant sources of reacti</p><p>　　Supplementary excitation controls such as line drop compensation and reactive power sharing are sometimes applied to maintain system voltage within tolerable limits. These co

56、ntrols must coordinate with system controls (such as reactive power equipment switching) that also regulate system voltage. Power system stabilizers (PSSs) are normally required to damp small system oscillations. PSSs mu

57、st be in service and properly tuned, but are not normally coordinated with any generator protection system</p><p>　　It is evident from the above review of excitation control systems that the AVR is a vital c

58、ontrol system that should be in service at all times. In North America. regional reliability criteria require that system transmission operators have positive assurance that generator excitation controls are in service a

59、nd that specified generator real and reactive power capability is available. Assurance of generator capability may require periodic testing of the controls to ensure their steady-state and </p><p>　　B. Turbi

60、ne Governor Control：</p><p>　　The major role of the turbine governor control is to maintain proper speed regulation and Load division for the generating units on the power system. Two types of control are us

61、ed "droop" and "frequency or isochronous (constant speed)," depending on the units operation and control requirements.</p><p>　　Droop (speed/load) control behaves with a characteristic th

62、at as load increases speed drops. With synchronous machines, their operation is locked at system frequency. Therefore, the droop governor becomes a load controller. As load increases, the governor signals the governor va

63、lves to open to maintain the established speed setting and accommodate the additional system load. Governor droop control prevents one generator from trying to pick up the entire additional load. Important benefits are t

64、h</p><p>　　Isochronous (frequency) governor control is used to operate the unit isolated from the power system. This control regulates the system frequency to the reference. This would be analogous to a huma

65、n operator adjusting the turbine to a specific speed (frequency) reference. During an islanded condition, this type of control is important to establish the system frequency at or near rated conditions. </p><p

66、>　　When required, only one unit is set in isochronous to provide the frequency reference for a system. If other units are connected, they are in droop control. This is done to avoid conflict, excessive loading, and un

67、loading between units.</p><p>　　Although two modes of control are available, "droop" and "isochronous，”the droop mode is almost universally used for generators interconnected in a large power

68、system. In the isochronous mode, the governor attempts to regulate the generator to a fixed frequency setting. Since a single generator has almost negligible effect on the frequency of a large power system, isochronous c

69、ontrol is not normally an effective mode.</p><p>　　During system disturbances, a sudden mismatch between generation and load may result from a loss of load, transmission capability, or generation, or any com

70、bination of those features. if the mismatch between generation and load is significant, system control actions will normally act first to quickly restore a rough balance between load and generation. These system control

71、actions are usually automatic under frequency load shedding, automatic generator shedding, or automatic application of braki</p><p>　　Many generators are not capable of operation for more than a very short t

72、ime outside narrow frequency deviations above or below rated frequency. Turbine governor controls will include supplementary limners to prevent the generator from operating in an islanded mode outside those frequency lim

73、its. These generators usually also have abnormal frequency protective equipment to disconnect them from the power system before the turbine can be damaged by operation outside prescribed limits. The turbine </p>&

74、lt;p>　　The system or regional dispatcher uses a common system controller or area controller to maintain system frequency and energy interchange schedules. This common control unit [automatic generator control (AGC) sy

75、stem] supervises each unit's turbine governor control, system frequency, and interchange schedules and dispatches corrections to the unit's turbine governor controllers accordingly.</p><p>　　During s

76、ome system disturbances where interconnected regions may become separated, scheduled interchanges can no longer be maintained during the immediate post disturbance time frame. If AGC is still in service, it may adjust tu

77、rbine governors in a fruitless attempt to maintain scheduled interchanges through transmission paths that no longer exist. Such blind AGC action may result in unacceptable load flows or system frequency deviations. Speci

78、al protection systems applied for system protection </p><p>　　It can be seen therefore that because of limited individual effect on system frequency, turbine governor controls have less interaction with syst

79、em and/or generator protection systems than generator excitation controls. However, proper setting of the governor controls is critical for maintenance of acceptable system frequency and reasonable unit load division aft

80、er disturbances. Further, turbine governor controls may become an integral part of special protection systems to maintain acceptable sy</p><p>　　C. System Control：</p><p>　　System control action

81、s are usually expected to mitigate the effect of disturbances before any equipment (including generators) becomes in danger of being physically damaged. 'These system controls are often called special protection sche

82、mes or remedial action schemes. It is expected that generator protective devices will coordinate with the generator capability to withstand abnormal operating conditions. However, it is important that such protective dev

83、ices also coordinate with the power system </p><p>　　Lender frequency load shedding is applied to prevent extended system operation at low frequency. The possibility of such operation arises when there is a

84、sudden and significant loss of generation or addition of load. Under frequency load shedding is usually expected to operate when there is such a large mismatch between load and generation that normal governor action cann

85、ot be expected to restore nominal frequency to prevent equipment damage from sustained low-frequency operation. Under frequenc</p><p>　　Voltage stability load shedding may be applied to prevent extended syst

86、em operation at low voltages. The possibility of such operation arises when there is a lack of reactive power required to maintain system、voltage levels within acceptable limits. This voltage stability load shedding is o

87、ften initiated by sustained low voltages with or without the presence of other indicators of insufficient reactive power availability. It is important that the voltage stability load shedding be coordinated wi</p>

88、<p>　　Other system control actions, which respond to low voltages, include the following: Reactor and capacitor switching to increase the amount of reactive power supplied to the system, HVDC fast ramping, tie line

89、 switching, and generator governor action to reduce the real power flow in the transmission system and, thereby, reduce reactive power demand. Again, generator protection, which responds to low voltages. and high current

90、s, should coordinate with such control actions.</p><p>　　Some special protection schemes separate out of step systems at suitable tie points. Generator protection, which responds to out-of-step conditions, s

91、hould also coordinate with such schemes. Generator out-of-step protection, under impedance protection and voltage controlled or restrained over-current protection may undesirably respond to out-of-step conditions before

92、system special protection schemes can act to remove the out-of-step condition.</p><p>　　Some other special protection schemes operate to prevent thermal overload from damaging equipment. Such schemes usually

93、 shed load, separate system tie lines, or start local generation or take emergency control of HVDC. It is important that generator protection, which might respond to unusually heavy load, should coordinate with any therm

94、al overload system special protection schemes. Some generator protection that may respond to heavy load includes stator over-current protection, stator overload </p><p><b>　　中文翻譯：</b></p>

95、<p>　　大型發(fā)電機干擾下發(fā)電機保護的性能</p><p><b>　　內(nèi)容摘要:</b></p><p>　　干擾是任何一個電力系統(tǒng)從一個穩(wěn)定運行狀態(tài)過渡到另一個穩(wěn)定狀態(tài)都存在的，保護用的繼電器在這個過渡時期會測量到不正常運行狀態(tài)。這篇文章觀點包括了在這個過渡過程中占據(jù)重要的控制措施，提供了在工業(yè)上裝置的技術(shù)指導(dǎo)及發(fā)電機保護和配網(wǎng)。</p>

96、<p><b>　　專業(yè)術(shù)語索引:</b></p><p>　　交流發(fā)電機勵磁、交流發(fā)電機保護、調(diào)速器、電力系統(tǒng)控制、渦輪機</p><p><b>　?、?說明:</b></p><p>　　所有電力系統(tǒng)每時每刻都會受到由于故障或主要負荷的開斷造成的瞬時性干擾。通常情況下，系統(tǒng)能在發(fā)電機勵磁機和渦輪機控制系統(tǒng)

97、的幫助下適應(yīng)新的穩(wěn)定狀態(tài)，許多附加的電力系統(tǒng)控制器設(shè)計方案能夠有用來幫助恢復(fù)到一個新的穩(wěn)定狀態(tài)。</p><p>　　從過去發(fā)生的主要事故中我們知道在發(fā)生故障的瞬間與發(fā)電機有關(guān)的保護有可能會動作。當系統(tǒng)出現(xiàn)干擾以避免不必要的的動作和使得電力網(wǎng)絡(luò)保持同步，優(yōu)化它們的協(xié)調(diào)性，對繼電器來說提供保護是非常重要的。</p><p>　　過去電力系統(tǒng)故障的簡潔描述就是發(fā)電機勵磁、渦輪機、調(diào)速器及電力系

98、統(tǒng)控制也包括在內(nèi)。這篇文章的主題就是討論在系統(tǒng)期間運行的發(fā)電機保護功能。</p><p><b>　　Ⅱ.電力系統(tǒng)干擾:</b></p><p>　　電力系統(tǒng)干擾就是指系統(tǒng)產(chǎn)生不正常運行狀態(tài)和系統(tǒng)從正常運行進入緊急狀態(tài)的情況。這些干擾可以分成兩類—小干擾和大干擾。大干擾是由于電力系統(tǒng)的規(guī)模和復(fù)雜性而向系統(tǒng)設(shè)備挑戰(zhàn)的情況。恰當?shù)谋Ｗo和控制措施當系統(tǒng)干擾出現(xiàn)后是非常需要的