继电保护中英文翻译(精).docx

Fun dame ntals of p rotect ion p ractice The purpose of an electrical po wer system is to gen erate and supply electrical en ergy to con sumers. The system should be desig ned and man aged to deliver this en ergy to the utilizatio n points with both reliability and economy. As these two requireme nts are largely opp osed, it is in structive to look at the reliability of a system and its cost and value to the con sumer. One hand ,The diagram mast make sure the reliability in system desig n,. On the other hand, high reliability should not be pu rsued as an end in itself, regardless of cost, but should rather be bala need aga inst econo my,tak ing. Security of supply can be bettered by improving plant desig n, in creas ing the spare cap acity margin and arranging alter native circuits to supply loads. Sub-divisio n of the system into zon es. each con trolled by switchgear in associati on with p rotective gear. pro vides flexibility duri ng no rmal op erati on and en sures a minimum of dislocati on followi ng a breakdow n. The greatest threat to the security of a supply system is the short circuit,which imp oses a sudde n and sometimes viole nt cha nge on system op erati on. The large curre nt which the n flows, acco mpanied by the localized release of a con siderable qua ntity of en ergy, can cause fire at the fault locati on, and mecha ni cal damage throughout the system, p articularly to mach ine and tran sformer windin gs. Rapid isolati on of the fault by the n earest switchgear will mini mize the damage and disr up ti on caused to the system. A po wer system rep rese nts a very large cap ital inv estme nt. To maximize the return on this outlay. the system must be loaded as much as po ssible. For this reas on it is n ecessary not only to pro vide a supply of en ergy which is attractive to prosp ective users by op erati ng the system ,but also to kee p the system in full op erati on as far as p ossible con ti nu ously, so that it may give the best service to the con