【机械类文献翻译】故障切除继电保护装置

翻译文献（英译中）

原文:

Fault—clearing Protective Relays(1)

Overcurrent relaying．Slow—speed relays．The most obvious effect of a fault is t o change the current in the faulted conductor from a normal value to an abnormall y large one．Therefore it is not surprising that the earliest methods of clearing fault s were based on the utilization of that effect(overcurrent)．Early methods included f uses，circuit breakers with

series trip coils，and slow—speed overcurrent relays．

Slow—speed overcurrent relays are mostly of the induction type．To obtain selec tivity without unnecessarily long delay，such relays usually have a delay which vari es inversely with the current．Both time and current settings are adjustable．Since t he fault current decreases，on account of the increased impedance of the line betw een the fault and the source．

as the fault is mo，ved farther from the source of power，it follows that the relay o perating time increases as the distance to the fault increases.

The time—distance curves change with such conditions as connected generating capacity and the connection or disconnection of other transmission lines，and ther efore，to ensure selectivity，curves should be checked for several conditions to asc ertain that．under the worst condition，an adequate interval exists between the oper ating times of relays 1 and 3，and, similarly，between each pair of relays on adjoi ning line sections．Coordination may be accomplished by judicious choice of both ti me settings and current settings．

If the relay current changes but little with fault location，the curve of relay time versus fault position becomes more like curve a than ike curve b．Such a condition

is likely to exist if the impedance of the protected section is small compared with the impedance between the generators and the protected section，as may well be t rue if the section is short and is fed

solely or principally from one end．Moreover curve a may hold even though the rel ay current does change with fault location，if，as is usually true，the relays are op erating on the minimum-time part of their time—current characteristic．Curve a repr esents an undesirable condition when several protected line sections are in cascad e，because the relay time of the lines

near the source of power becomes increasingly long．

If a line section is long or has power sources at each end，the relay current wi ll vary considerably with fault location．But，even if the current varies enough to gi ve a curve like b，the operating time of a relay near the generator is usually some what longer than that of a relay farther from the generator，though not so much lo nger as in curve a．

By the use of graded time settings，overcurrent relays can always be made to work selectively on a radial transmission or distribution system．With graded setting s，and with the addition of directional relays，overcurrent relays can be made to w ork selectively on a loop system fed from one point．But on a loop fed sometimes from one point and sometimes from another，or on a network more complex than a loop，it is difficuh，if not impossible，to choose settings for overcurrent relays so t hat the relays will work selectively for all fault locations and for all operating conditi ons．

译文:

故障切除继电保护装置(1)

现在来谈谈过电流继电保护装置，特别是延时过电流继电保护装置。故障出现时，最明