影響電力系統(tǒng)運(yùn)行的因素.doc

Hazards to Power System OperationThe operation of electric power systems may be disturbed as the result of a number of causes. The troubles on the electric circuits are usually in the form of broken conductors or circumstances in which conductors are temporarily (or permanent) connected to each other or to ground. Regardless of the cause of the disturbances, such troubles seriously interfere with the flow of power and require corrective action.Overhead lines are vulnerable to troubles caused by lightning. When lightning strikes a line or a nearby object, a transient voltage is created on the line ,Hihg-voltage circuits have large spacing between conductors and from conductors to grounded objects, such as towers. Direct strokes to such lines are usually diverted to ground through overhead ground wires and may cause no interference with operation. Occasionally strokes terminate directly on the power conductors and introduce onto them transient transient voltages of such magnitude that archer across insulator strings may result. Once an arc is established, power current flows through it until the circuit is deenergized . Lightning voltages may be of high magnitude but are of very short duration; their time is measured in microseconds. As a result, their effects are most noticeable at the point where the stroke occurs. Distribution lines, which operate at perhaps 12kV or less, are mounted on relatively small insulators, which may be flashed over by the voltage induced in a line even though the lightning stroke does not contact the line. Such resulting arcs interfere with operation and usually are eliminated by deenergizing the line. When the line is deenergized . The arc is extinguished and, very commonly, the line may be reenergizing immediately.Overhead lines are subjected to wind and sleet. Although designed to withstand ordinary storm loading, practically they can not be designed for the extreme condition of sleet or wind loading. Hence, occasional line failures occur as a result of these causes. Failures caused by wind or sleet are usually of such nature that repairs must be made before the line may be reenergize .Foreign objects may contact a line and cause damage, which necessitates removal of the line from service. Airplanes may fly into a line, an automobile may knock apole , a construction worker may run a crane into a line ,or an excavator may dig up a cable. Birds, squirrels , snakes and other animals occasionally short-circuit lines and cause outages.Generators, transformers , lines ,or other components may be switched out of service for normal or routine maintenance. When switching operations occur, transients are set up on the power system which sometimes produce serous overvoltages. Such overvoltages in turn may cause flashover of insulators or puncture of solid insulation.Equipment sometimes fails without any particular direct cause. Failure may be due to inadequate design. previous overloads, or natural deterioration of equipment.Human errors may produce power-system outages. Switches may be opened unintentionally. Cutting off loads; temporary grounding electrodes may be put on energized circuits by mistake; equipment handled by hotline devices may be dropped. Such occasions, although rare, must be considered as hazard possibilities in power-system design. 影響電力系統(tǒng)運(yùn)行的因素影響電力系統(tǒng)正常運(yùn)行的因素很多。電路故障的形式通常是導(dǎo)體斷裂。導(dǎo)體暫時(shí)（或永久地）相間接地。不管故障的原因是什么，這些故障都嚴(yán)重干擾電流的輸送，需要采取補(bǔ)救措施。雷電容易影響架空線路。當(dāng)雷電擊中輸電線路或其附近物體時(shí)，線路上產(chǎn)生暫態(tài)電壓。高壓電路的相間以及相對(duì)接地體如桿塔）間均有很大的絕緣距離。當(dāng)接地線遭受雷擊時(shí)，雷電可經(jīng)過架空地線流入大地，不會(huì)給運(yùn)行造成什么影響。但是，有時(shí)輸電線路會(huì)遭受雷擊，從而在輸電線路上產(chǎn)生倡但很高的暫態(tài)電壓：這種電壓會(huì)引起線路絕緣子串的電弧放軌一旦絕緣子串上建立電弧，電流會(huì)通過它流動(dòng)而引起線路斷電。雷電過電壓具有很高的幅值，但持續(xù)時(shí)間極短，以微秒計(jì)算。由此可見，雷電對(duì)系統(tǒng)正常運(yùn)行影響很大。配電線路的運(yùn)行電壓通常為12千伏或更低，它們由相對(duì)較少的絕緣子串懸掛，所以即使雷電不足以擊倒輸電線路。它也會(huì)在線路上引起感應(yīng)電壓，從而導(dǎo)致絕緣子串閃絡(luò)。這種電弧放電會(huì)影響系統(tǒng)運(yùn)行，通?？赏ㄟ^斷電來(lái)消除故障。跑路一斷，電弧熄滅，此時(shí)線路可重新合閘架空線易受到大風(fēng)和冰雹的侵襲。雖然線路設(shè)計(jì)時(shí)需考慮耐受風(fēng)暴的影響，但是不可能依據(jù)最惡劣的氣候條件來(lái)設(shè)計(jì)。所以氣候條件也會(huì)引起輸電線路故障，這種故障必須在線路重新供電之前排除。外來(lái)物體有可能接觸線路造成損害，此時(shí)需切斷線路。飛機(jī)可能會(huì)碰到線路，汽車可能會(huì)撞倒電線桿，建筑工人的起重機(jī)可能會(huì)撞到導(dǎo)線，挖掘機(jī)也可能會(huì)挖出電纜。鳥兒、松鼠、蛇和其它動(dòng)物偶爾會(huì)使線路短路造成停電。在正?；蚶袡z修時(shí)，發(fā)電機(jī)、變壓器、輸電線路或其它設(shè)備需退出運(yùn)行。當(dāng)開關(guān)操作時(shí)，系統(tǒng)中會(huì)出現(xiàn)暫態(tài)過程，從而引起非常嚴(yán)重的暫態(tài)過電壓。這種過電壓會(huì)造成絕緣子串閃絡(luò)或固體絕緣擊穿。有時(shí)設(shè)備產(chǎn)生故障并沒有什么特別的直接原因。故障可能歸因于設(shè)計(jì)不當(dāng)、過載，或者設(shè)備的自然老化。人為過失也會(huì)導(dǎo)致電力系統(tǒng)停電事故。開關(guān)可能會(huì)被無(wú)意中拉開而中斷負(fù)荷；臨時(shí)接地體可能被錯(cuò)誤地與帶電回路相連。由帶電裝置控制的設(shè)備可能被接地。這種情況雖然很少，但在電力系統(tǒng)的設(shè)計(jì)當(dāng)中必須考慮它們可能帶來(lái)的危害。New Words1. magnitude 幅值 2. arcover 電弧放電，跳火，飛弧，擊（打）穿 3. insulator絕緣體，絕緣子 4. arc弧 5. reenergize斷路（開） 6. kV千伏 7. induce感應(yīng) 8. reenergize 使又通上電流 9. necessitate 使成為必要 10. excavator挖掘機(jī) 11. short-circuit使短咱 12. outage停電 13. transformer變壓器 14. overvoltage 過電壓 15. unintentionally 無(wú)意地 16. grounding接地（電） 17. electrode