【正文】 n accordance with this principle. The phase fault highset unit and the earthfault unit are associated with the acceleration logic incorporated inside the relay, the lowset unit being used to protect against overloads and is totally independent of the logic. In order to maintain a high degree of security, selective (or graded) backup timedelays are incorporated, which trip under fault conditions even in the event of a fault occurring within the wiring connecting the relays. Differential protection This type of protection operates on the principle of current parison in the same phase but at the two extremities of the protected equipment, (cable: SOLKORRF, transformer: DMS7002, DTT7031, rotating machines: DMS 7001, DTM 7033, IAG 7034 or bus bars: IAG 7034) and has two main advantages: ? It may be instantaneous, because it only reacts to faults inside the protected zone, ? It will operate for the transfer of energy in either direction, which is particularly important in the event of multiple sources. It may also allow a grading step to be eliminated, thus reducing the tripping time for faults on the upstream work. To counterbalance these advantages however, it requires pilot links (SOLKORRF) and matched class X current transformers are generally remended with stabilising resistors for the differential protection of transformers, rotating machines and busbars. The differential relays for cable protection, type SOLKORRF, operate on a special principle ? They do not pare individually the currents in each phase, but rather a bination of the three currents. ? The advantage of this system is that only one pair of pilot wires is required, but the operating levels are different for faults on different phases. Directional protection When a substation is supplied by two cables or two transformers in parallel, the protection on these two feeders (in the upstream substation) would operate simultaneously for a fault affecting one of them. To obtain selective protection it is necessary to use either differential or directional relays. In the latter case phase directional overcurrent relays type RMSD7921 or ITD7111 should be installed on each iner. The directional element of these relays checks the phase angle between the current and voltage of one phase, and allows the overcurrent unit to operate if this phase angle indicates current in the reverse direction. RMSD 7000 relays, with the FFT input signal treatment, check the phase angle between the fundamental of current and voltage. As a result they remain stable and selective even in works containing high levels of harmonics. The time delay of the directional relay is chosen to be selective with the upstream relays, and thus the loop is first opened (by tripping the correct LV breaker), followed by the upstream protection isolating the faulty feeder. Alternatively, the upstream breaker may be opened by sending an intertrip signal from the LV directional relay to accelerate fault elimination. 1 簡介 繼電保護裝置可以認為是 電力 系統(tǒng)設(shè)備 裝置中的大腦 部分。 英文翻譯 (譯文 ) 英 文 名 稱 Application guide for the choice of protective relays 中 文 名 稱 繼電保護選擇的應用指導 學 生 姓 名 學 號 系、年級專業(yè) 電氣工程系、 10 電氣工程及其 自動化 指 導 教 師 職 稱 2021 年 1 月 20 日 Application guide for the choice of protective