【正文】 結(jié)果他們保持穩(wěn)定和選擇性甚至在網(wǎng)絡(luò)含有高水平的諧波。 差動(dòng)保護(hù) 這一保護(hù)的原則是比較同一相上電流的大小，單由兩個(gè)繼電保護(hù)裝置來執(zhí)行保護(hù)。 分級間隔可能會減少如果需要 ,時(shí)間小于 1秒， 使用繼電器與高穩(wěn)定性定時(shí)器電路 則在 250ms左右 (ITG 7000或均方根 700/7000繼電器 )。他們必須要能夠快速的感知 在短路情況下產(chǎn)生的 電流 沖擊變化量 并 在 短時(shí)間內(nèi) 做出 正確的反應(yīng) （ 還要考慮到 電應(yīng)力和熱應(yīng)力 的承受范圍 ） 它的另一個(gè)基礎(chǔ)特性就是 選擇性 ,能夠正確反應(yīng) 故障處 短路 以 維持供電 網(wǎng)絡(luò)的健康穩(wěn)定。 2 高電壓工業(yè)和配電網(wǎng)絡(luò)的保護(hù) 繼電保護(hù)在電能 網(wǎng)絡(luò)中扮演這非常重要的角色，他們是否能夠 對 器件和全體設(shè)備 作出正確的保護(hù)動(dòng)作 ，這為能否提供高質(zhì)量 電能提供了 保證。同時(shí)，對器件的穩(wěn)定性和安全的性的要求也在不斷的提高。 為了使 電力系統(tǒng)的 穩(wěn)定性和安全性達(dá)到最 優(yōu)化 的 需求 ， 規(guī)定我們 在靠近電力線路斷路器側(cè) 配置 使用 獨(dú)立的 繼電器 來控制 。 the Fast Fourier Transformation. Using this feature a large number of harmonics are taken into account to build currents with a true RMS value. This permits relays to be desensitised to certain harmonics for special applications. Furthermore relays of the RMSA series are autonomous in that they can operate without an auxiliary supply by deriving their power from the CTs. PROTECTION AGAINST PHASE TO PHASE FAULTS Overcurrent protection is the basic protection used in electrical power works. They must be both sensitive and rapid in order to minimise the stress imposed on the equipment during the fault period (electrodynamic and thermal stresses). It is also essential that they should be selective, that is capable of eliminating only the faulty element whilst maintaining the supply to healthy parts of the work. Choice of the time/current characteristic Overcurrent protection relays are mainly characterised by their time/current characteristic. Several types are available: ? Independent or definite time relays (whose operating time is independent of current level) ? Dependent or inverse time relays (whose operating time depends on the current level). This last type of relay may be subdivided into three categories according to the IEC standard 2554: ? Inverse time relays (ITG7200 series ) ? Very inverse time relays (ITG7300 series ) ? Extremely inverse time relays (ITG7400 series ) ? Digital multicurve overcurrent relay (RMS700, RMS7000, RMST7000 and RMSA7000 series) No particular criterion exists for the systematic choice of one or other type of relay. However, dependent time relaying is preferable in the following cases where: ? The operation of the work includes highlevel shorttime overloads, ? Magising inrush currents at switchon may be considerable for several tenths of a second, ? Relay operation must be coordinated with a large number of fuses. On the other hand, independent time relays are preferable when the shortcircuit level is very high, or when it is likely to vary widely at a given point (for example when a work is supplied from small generators whose shortcircuit decrement curve falls off rapidly). As a basic rule, however, there is a general tendency to use independent time relays in Continental Europe and dependent time in AngloSaxon countries. Timedelayed overcurrent relays lend themselves to chronological selectivity. This however is not without a certain inconvenience, in that fault clearance time increases closest to the source, where shortcircuit levels are the highest. It is thus necessary to minimise the grading interval . The grading interval normally used for electronic protection relays is 400 ms, which is obtained by summating the following: ? Breaker fault clearance time, ? Summation of the time errors of the two relays, ? Overshoot of the upstream relay, ? Safety margin of approximately 100 ms. When transformer feeder protection is being considered it is advisable to use relays having an instantaneous highset unit. This