電力系統(tǒng)故障畢業(yè)論文中英文資料外文翻譯文獻

1、畢業(yè)設計電力系統(tǒng)故障中英文資料外文翻譯文獻Faults on Power SystemsEach year new desig n of power equipme nt bring about in creased reliability of operati on. Nevertheless, equipme nt failures and in terfere nee by outside sources occasi on ally result in faults on electric power systems. On the occurrence of a fault , cu

2、rrent an voltage 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 equipme nt is not promptly disc onn ected from the rema in der of the system, damage may result to other pieces of operati ng

3、 equipme nt.A faulty is the uninten ti onal or inten tio nal conn ect ing together of two or more con ductors which ordin arily operate with a differe nce of pote ntial betwee n them. The connection betwee n the con ductors may be by physical metallic con tact or it may be through an arc. At the fau

4、lt, the voltage betwee n the two parts is reduced to zero in the case of metal-to-metal con tacts, 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 curre nts will usually be much

5、 greater tha n the desig ned thermal ability of the con diti on in the lines or machines feeding the fault . The resultant rise in temperature may cause damage by the ann eali ng of con ductors and by the charri ng of in sulati on. In the period duri ng which the fault is permitted to exist, the vol

6、tage on the system in the near vicinity of the fault will be so low that utilization equipment will be in operative. It is appare nt that the late con diti ons that exist duri ng a fault, and provide equipme nt properly adjusted to ope n the switches n ecessary to disc onn ect the faulted equipme nt

7、 from the rema nding of the system. Ordinarily it is desirable that no other switches on the system are opened, as such behavior would result i n unn ecessary modificati on the system circuits.A dist in cti on must be made betwee n and an overload. An overload implies only that loads greater tha n t

8、he desig ned values have bee n imposed on system. Un der such a circumsta nce 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 rema in der of the system. The curre nt in the overload equipme nt are

9、 high and may exceed the thermal design limits. Nevertheless, such currents are substantially lower than in the case of a fault. Service freque ntly may be maintain ed, but at below-sta ndard voltage.Overloads are rather com mon occurre nces in homes. For example, a housewife might plug five waffle

10、irons into the kitchen circuit during a neighborhood part. Such an overload, if 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

11、 when currents above specified values persist. Distributi on tran sformers are sometimes overloads as customers in stall more and more appliances. The continuous monitoring of distribution circuits is necessary to be certain that tran sformers sizes are in creased as load grows.Faults of many types

12、and causes may appear on electric power systems. Many of us in our homes have see n frayed lamp cords which permitted the two con ductors of the cord to come in con tact with each other. When this occurs, there is a result ing flash, and if breaker or fuse equipme nt fun cti ons properly, the circui

13、t is ope ned.Overhead lin es, for the most part, are con structed of bare con ductors. There are sometimes accidentally brought together by action of wind, sleets, trees, cranes, airplanes, or damage to supporting structures. Overvoltages due to light ing or switch ing nay cause flashover of support

14、 ing or from con ductor to con ductor. Con tam in ati on on in sulators sometimes results in flashover even duri ng no rmal voltage con diti ons.The con ductors of un dergro und cables are separated from each and from gro und by solid in sulati on, which nay be oil-impregnated paper or a plastic suc

15、h polyethylene. These materials undergo some deterioration with age, particularly if overloads on the cables have resulted 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 o

16、f which react unfavorably with the insulation. Deterioration of the insulation may result in failure of the material to retain its insulating properties, and short circuits will develop betwee n the cable con ductors. The possibility of cable failure is in creased if lighte ning or switch ing produc

17、es tran sie nt voltage of abno rmally high values betwee n the con ductors.Tran sformer failures may be the result of in sulati on deteriorati on comb ined with overvoltage due to light ning or switch ing tran sie nts. Short circuit due to in sulati on failure betwee n adjace nt turns of the same wi

18、nding may result from suddenly applied overvoltage. Major insulation may fail, permitting arcs to be established betwee n primary and sec on dary windings or betwee n winding and groun ded metal parts such as the core or tank.Gen erators may fail due to breakdow n of the in sulati on betwee n adjace

19、 nt 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 winding and the gro un ded steel structure in which the coils are embedded. Breakdow n betwee n differe nt windings lying in the same slot results in sho

20、rt-circuit ing exte nsive sect ion of mach ine.Bala need three-phase faults, like bala need three-phase loads, may be han dled on a lin eto-n eutral basis or on an equivale nt sin gle-phase basis. Problems may be solved either in terms of volts, amperes, and ohms. The handing of faults on single-pha

21、se lines is of course identical to the method of handing three-phase faults on an equivale nt sin gle-phase basis.Faults may be classified as permanent or temporary. Permanent faults are those in which insulation failure or structure failure produces damage that makes operati on of the equipme nt im

22、possible and requires repairs to be made. Temporary faults are those which may be removed by dee nergiz ing the equipme nt for a short period of time, short circuits on overhead lines frequently are of this nature. High winds may cause two or more con duct ions to swi ng together mome ntarily. Durin

23、g the short period of con tact. An arc is formed which may con ti nue as long as line rema ins en ergized. However, if automatic equipme nt can be brought into operati on to service as soon as the are is ext in guished. Arcs across in sulators due to overvoltages from lighting or switching transient

24、s usually can be cleared by automatic circuit-breaker operatio n before sig ni fica nt structure damage occurs.Because of this characteristic of faults on lines, many companies operate following a procedure known as high-speed reclos ing. On the occurre nee of a fault, the line is promptly dee nergi

25、zed by ope ning the circuit breakers at each end of the line. The breakers rema in ope n long eno ugh for the arc to clear, and then reclose automatically. In many instances service is restored in a fraction of a second. Of course, if structure damage has occurred and the fault persists, it is neces

26、sary for the breakers to reopen and lockope n.電力系統(tǒng)故障每年新設計的電力設備都使系統(tǒng)的可靠性不斷提高，然而，設備的使用不當以及一些偶然遇到 的外在因素均會導致系統(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。此時若故障設備不立即從系統(tǒng)中切除的話，則會造成其他運行設備的 損壞。故障是由于有意或無意地使兩個或更多的導體接觸造成的。導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)絡流

27、至故障處。此短路電流通常會大 大超出導線以及供電發(fā)電機的熱承受能力，其結果，溫度的升高會導致導體燒毀或絕緣焦化。在允 許的期限內(nèi)，最靠近故障處的電壓會變得很低，致使用電設備無法正常運行。顯然，系統(tǒng)設計者必 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)好的設備，以 便驅動為將故障設備切除所必須斷開的開關能夠跳閘。通常希望此時系統(tǒng)無其他開關打開，否則會 導致系統(tǒng)線路不必要的修改。過負荷與故障是兩個概念。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

28、。過負荷設備的電流變大而超過預定的熱極限，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。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 流超出預定值時迅速切斷電路。當用戶安裝的用電器增加時，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

29、燈電線，使 得其兩根導線相觸，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體假設的，又是由于風、雨、雷、或大樹、起重機，飛機及支撐物的 損壞等因素會使導線偶然碰到一起。由雷電或開關瞬變過程中引起的過電壓會在支撐物或導體之間 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線與導線和導線與地隔 開。這些絕緣會隨著時間的流逝而老化，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致導線 短路。

30、電纜故障的可能性會因雷電或開關瞬間引起的導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、開關瞬變過程導致的過高壓造成的。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，其結果會導致發(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之間。同一槽內(nèi)不同繞組之間的絕 緣損壞會導致電機大范圍短路。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?？梢酝ㄟ^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構上的損壞，致使設備不能維修 則無法運行。暫時性故障指通過給設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 風可能會使兩根導線瞬時間碰在一起，并產(chǎn)生電弧。只要線路通電，此電弧會一直存在。然而如果 能借助自動化設備使導線迅速斷電的話，