影响电力系统运行的因素.doc

Hazards to Power System Operation
⑴The operation of electric power systems may be disturbed as the result of a number olures 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 .
 
影响电力系统运行的因素
⑴影响电力系统正常运行的因素很多。电路故障的形式通常是导体断裂。导体暂时（或永久地）相间接地。不管故障的原因是什么，这些故障都严重干扰电流的输送，需要采取补救措施。
⑵雷电容易影响架空线路。当雷电击中输电线路或其附近物体时，线路上产生暂态电压。高压电路的相间以及相对接地体．如杆塔）间均有很大的绝缘距离。当接地线遭受雷击时，雷电可经过架空地线流入大地，不会给运行造成什么影响。但是，有时输电线路会遭受雷击，从而在输电线路上产生倡但很高的暂态电压：这种电压会引起线路绝缘子串的电弧放轨一旦绝缘子串上建立电弧，电流会通过它流动而引起线路断电。雷电过电压具有很高的幅值，但持续时间极短，以微秒计算。由此可见，雷电对系统正常运行影响很大。配电线路的运行电压通常为12千伏或更低，它们由相对较少的绝缘子串悬挂，所以即使雷电不足以击倒输电线路。它也会在线路上引起感应电压，从而导致绝缘子串闪络。这种电弧放电会影响系统运行，通常可通过断电来消除故障。跑路一断，电弧熄灭，此时线路可重新合闸架空线易受到大风和冰雹的侵袭。
⑶虽然线路设计时需考虑耐受风暴的影响，但是不可能依据最恶劣的气候条件来设计。所以气候条件也会引起输电线路故障，这种故障必须在线路重新供电之前排除。
⑷Foreign 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.
⑸Generators, 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 prod