電力系統(tǒng)故障畢業(yè)論文中英文資料外文翻譯文獻

1、電力系統(tǒng)故障 中英文資料外文翻譯文獻Faults on Power SystemsEach year new design of power equipment bring about increased reliability of operation. Nevertheless, equipment failures and interference by outside sources occasionally result in faults on electric power systems. On the occurrence of a fault , current an vol

2、tage conditions become abnormal, the delivery of power from the generating station to the loads may be unsatisfactory over a considerable area, and if the faulted equipment is not promptly disconnected from the remainder of the system, damage may result to other pieces of operating equipment.A fault

3、y is the unintentional or intentional connecting together of two or more conductors which ordinarily operate with a difference of potential between them. The connection between the conductors may be by physical metallic contact or it may be through an arc. At the fault, the voltage between the two p

4、arts is reduced to zero in the case of metal-to-metal contacts, or to a very low value in case the connection is through an arc. Currents of abnormally high magnitude flow through the network to the point of fault. These short-circuit currents will usually be much greater than the designed thermal a

5、bility of the condition in the lines or machines feeding the fault . The resultant rise in temperature may cause damage by the annealing of conductors and by the charring of insulation. In the period during which the fault is permitted to exist, the voltage on the system in the near vicinity of the

6、fault will be so low that utilization equipment will be inoperative. It is apparent that the late conditions that exist during a fault, and provide equipment properly adjusted to open the switches necessary to disconnect the faulted equipment from the remanding of the system. Ordinarily it is desira

7、ble that no other switches on the system are opened, as such behavior would result in unnecessary modification the system circuits. A distinction must be made between and an overload. An overload implies only that loads greater than the designed values have been imposed on system. Under such a circu

8、mstance the voltage at the overload point may be low, but not zero. This undervoltage condition may extend for some distance beyond the overload point into the remainder of the system. The current in the overload equipment are high and may exceed the thermal design limits. Nevertheless, such current

9、s are substantially lower than in the case of a fault. Service frequently may be maintained, but at below-standard voltage.Overloads are rather common occurrences in homes. For example, a housewife might plug five waffle irons into the kitchen circuit during a neighborhood part. Such an overload, if

10、 permitted to continue, would cause heating of the wires from the power center and might eventually start a fire. To prevent such trouble, residential circuits are protected by fuses or circuit breakers which open quickly when currents above specified values persist. Distribution transformers are so

11、metimes overloads as customers install more and more appliances. The continuous monitoring of distribution circuits is necessary to be certain that transformers sizes are increased as load grows.Faults of many types and causes may appear on electric power systems. Many of us in our homes have seen f

12、rayed lamp cords which permitted the two conductors of the cord to come in contact with each other. When this occurs, there is a resulting flash, and if breaker or fuse equipment functions properly, the circuit is opened.Overhead lines, for the most part, are constructed of bare conductors. There ar

13、e sometimes accidentally brought together by action of wind, sleets, trees, cranes, airplanes, or damage to supporting structures. Overvoltages due to lighting or switching nay cause flashover of supporting or from conductor to conductor. Contamination on insulators sometimes results in flashover ev

14、en during normal voltage conditions.The conductors of underground cables are separated from each and from ground by solid insulation, which nay be oil-impregnated paper or a plastic such polyethylene. These materials undergo some deterioration with age, particularly if overloads on the cables have r

15、esulted in their operation at elevated temperature. Any small void present in the body of the insulating material will results in ionization of the gas contained therein, the products of which react unfavorably with the insulation. Deterioration of the insulation may result in failure of the materia

16、l to retain its insulating properties, and short circuits will develop between the cable conductors. The possibility of cable failure is increased if lightening or switching produces transient voltage of abnormally high values between the conductors.Transformer failures may be the result of insulati

17、on deterioration combined with overvoltage due to lightning or switching transients. Short circuit due to insulation failure between adjacent turns of the same winding may result from suddenly applied overvoltage. Major insulation may fail, permitting arcs to be established between primary and secon

18、dary windings or between winding and grounded metal parts such as the core or tank.Generators may fail due to breakdown of the insulation between adjacent turns in the same slot, resulting in a short circuit in a single turn of the generator. Insulation breakdown may also occur between one of the wi

19、nding and the grounded steel structure in which the coils are embedded. Breakdown between different windings lying in the same slot results in short-circuiting extensive section of machine.Balanced three-phase faults, like balanced three-phase loads, may be handled on a lineto-neutral basis or on an

20、 equivalent single-phase basis. Problems may be solved either in terms of volts, amperes, and ohms. The handing of faults on single-phase lines is of course identical to the method of handing three-phase faults on an equivalent single-phase basis.Faults may be classified as permanent or temporary. P

21、ermanent faults are those in which insulation failure or structure failure produces damage that makes operation of the equipment impossible and requires repairs to be made. Temporary faults are those which may be removed by deenergizing the equipment for a short period of time, short circuits on ove

22、rhead lines frequently are of this nature. High winds may cause two or more conductions to swing together momentarily. During the short period of contact. An arc is formed which may continue as long as line remains energized. However, if automatic equipment can be brought into operation to service a

23、s soon as the are is extinguished. Arcs across insulators due to overvoltages from lighting or switching transients usually can be cleared by automatic circuit-breaker operation before significant structure damage occurs.Because of this characteristic of faults on lines, many companies operate follo

24、wing a procedure known as high-speed reclosing. On the occurrence of a fault, the line is promptly deenergized by opening the circuit breakers at each end of the line. The breakers remain open long enough for the arc to clear, and then reclose automatically. In many instances service is restored in

25、a fraction of a second. Of course, if structure damage has occurred and the fault persists, it is necessary for the breakers to reopen and lock open.電力系統(tǒng)故障每年新設(shè)計的電力設(shè)備都使系統(tǒng)的可靠性不斷提高，然而，設(shè)備的使用不當以及一些偶然遇到的外在因素均會導(dǎo)致系統(tǒng)故障的發(fā)生。發(fā)生故障時，電流、電壓變化得不正常，從電廠到用戶的送點在相當大得內(nèi)不令人滿意。此時若故障設(shè)備不立即從系統(tǒng)中切除的話，則會造成其他運行設(shè)備的損壞。故障是由于有意或無意地使兩個或

26、更多的導(dǎo)體接觸造成的。導(dǎo)體間本來是有電位存在的，而這種接觸可能是金屬性接觸，也可能是電弧引起的。如果是前者造成的故障，則兩部分導(dǎo)體之間電壓下降為零；若為后者，則電壓變得很低，超常的大電流經(jīng)過網(wǎng)絡(luò)流至故障處。此短路電流通常會大大超出導(dǎo)線以及供電發(fā)電機的熱承受能力，其結(jié)果，溫度的升高會導(dǎo)致導(dǎo)體燒毀或絕緣焦化。在允許的期限內(nèi)，最靠近故障處的電壓會變得很低，致使用電設(shè)備無法正常運行。顯然，系統(tǒng)設(shè)計者必須事先考慮到故障可能發(fā)生在什么地方，能夠推測出故障期間的各種情況，提供調(diào)節(jié)好的設(shè)備，以便驅(qū)動為將故障設(shè)備切除所必須斷開的開關(guān)能夠跳閘。通常希望此時系統(tǒng)無其他開關(guān)打開，否則會導(dǎo)致系統(tǒng)線路不必要的修改。過負荷

27、與故障是兩個概念。過負荷僅指施加于系統(tǒng)的負荷超過了設(shè)計值。發(fā)生這種情況時，過負荷處的電壓可能很低，但并不等于零。這種電壓不足的情形可能會超過過負荷處蔓延一定距離，進而影響系統(tǒng)其它部分。過負荷設(shè)備的電流變大而超過預(yù)定的熱極限，但是這種情況比發(fā)生故障時的電流要小。此時，供電雖然往往能維持，但電壓較低。過負荷的情況在家里發(fā)生，例如請街坊鄰居聚會時，女主人可能將五個化夫餅干烘烤器的插頭同時插入廚房的插座，諸如次類的過負荷倘若不能迅速處理的話，就會造成電力線發(fā)熱甚至釀成火災(zāi)。為了避免這種情況的發(fā)生，須采用保險絲或短路器來保護住宅區(qū)電路免受損壞。斷路器會在電流超出預(yù)定值時迅速切斷電路。當用戶安裝的用電器增

28、加時，也會超過變壓器負荷能力，因此有必要不時地監(jiān)視配電線路以確保在負荷增加時變壓器的容量也相應(yīng)增加。電力系統(tǒng)會發(fā)生各種類型，由各種原因引起的故障。我們在家里看到過破損的照明燈電線，使得其兩根導(dǎo)線相觸，并會發(fā)出弧光。如果此時斷路器或保險絲能夠正常工作，則電路能被自動切斷。大部分架空明線是用裸導(dǎo)體假設(shè)的，又是由于風(fēng)、雨、雷、或大樹、起重機，飛機及支撐物的損壞等因素會使導(dǎo)線偶然碰到一起。由雷電或開關(guān)瞬變過程中引起的過電壓會在支撐物或?qū)w之間產(chǎn)生電弧，即使在電壓正常的情況下，絕緣材料的污染也會引起電弧。通常采用油浸電纜紙或聚乙烯一類固體塑料絕緣材料將埋地電纜中的導(dǎo)線與導(dǎo)線和導(dǎo)線與地隔開。這些絕緣會隨著

29、時間的流逝而老化，尤其是在過負荷引起高溫下運行時候更是如此。絕緣材料內(nèi)的空隙會造成氣體的電離，其生成物對絕緣不利。絕緣材料老化會引起絕緣性能下降而導(dǎo)致導(dǎo)線短路。電纜故障的可能性會因雷電或開關(guān)瞬間引起的導(dǎo)線的電壓驟然變高而增加。變壓器故障可能是由絕緣老化、加上雷電、開關(guān)瞬變過程導(dǎo)致的過高壓造成的。同一繞組相鄰線圈之間由于絕緣問題造成的短路可能是由于突然遇到外加高壓電所致。絕緣失敗會在一次繞組與二次繞組之間或繞組與接地金屬部件如鐵芯或變壓器外殼之間產(chǎn)生電弧。發(fā)電機故障可能是由于同一槽中相鄰線圈之間絕緣被破壞而造成的，其結(jié)果會導(dǎo)致發(fā)電機匝內(nèi)短路。絕緣損壞也可能發(fā)生在某一繞組與定子鐵芯的接地鋼架構(gòu)之間。同一槽內(nèi)不同繞組之間的絕緣損壞會導(dǎo)致電機大范圍短路。像處理平衡三相負荷一樣，處理平衡三相故障也是依照基于由火線到零線的電路或等效單相電路的原則進行。可以通過電壓、電流和電阻的規(guī)律求解問題。當然，單相線路上故障的處理方法也可以用于在單相等效電路下三相故障的處理中。故障有永久性故障及暫時性故障之分。永久性故障指絕緣或結(jié)構(gòu)上的損壞，致使設(shè)備不能維修則無法運行。暫時性故障指通過給設(shè)備臨時斷電即可排出的故障，架空線路往往就有這個特點。大風(fēng)可能會使兩根導(dǎo)線瞬時間碰在一起，并產(chǎn)生電弧。只要線路通電，此電弧會一直存在。然