电力系统中英文翻译

电力系统中英文翻译内容摘要：

erreach will not extend beyond the reach of the firstzone unit of the adjoining line 外文翻译 5 section under the same conditions, or (2) with a time delay long enough to be selective with the secondzone time of the adjoining section, as shown in Fig. 2. In this connection, any underreaching tendencies of the relays on the adjoining line sections must be taken into account. When an adjoining line is so short that it is impossible to get the required selectivity on the basis of react, it bees necessary to increase the time delay, as illustrated in Fig. 2. Otherwise, the time delay of the secondzone unit should be long enough to provide selectivity with the slowest of (1) busdifferential relays of the bus at the other end of the line(2)transformerdifferential relays of transformers on the bus at the other end of the line, or (3) line relays of adjoining line sections. The interrupting time of the circuit breakers of these various elements will also affect the secondzone time. This secondzone time is normally about second to second. The thirdzone unit provides backup protection for faults in adjoining line sections. 外文翻译 6 So far as possible, its reach should extend beyond the end of the longest adjoining line section under the conditions that cause the maximum amount of underreach, namely, arcs and intermediate current sources. Figure 3 shows a normal backup characteristic. The thirdzone time delay is usually about second to second. To reach beyond the end of a long adjoining line and still be selective with the relays of a short line, it may be necessary to get this selectivity with additional time delay, as in Fig. 4. THE EFFECT OF ARCS ON DISTANCERELAY OPERATION The critical arc location is just short of the point on a line at which a distance relay39。 s operation changes from highspeed to intermediate time or from intermediate time to backup time. We are concerned with the possibility that an arc within the highspeed zone will make the relay operate in intermediate time, that an arc within the intermediate zone will make the relay operate in backup time, or that an arc within the backup zone will prevent relay operation pletely. In other words, the effect of an arc may be to cause a distance relay to underreach. For an arc just short of the end of the first or highspeed zone, it is the initial characteristic of the arc that concerns us. A distance relay39。 s firstzone unit is so fast that, if the impedance is such that the unit can operate immediately when the arc is struck, it will do so before the arc can stretch appreciably and thereby increase its 外文翻译 7 resistance. Therefore, we can calculate the arc characteristic for a length equal to the distance between conductors for phasetophase faults, or across an insulator string for phasetoground faults. On the other hand, for arcs in the intermediatetime or backup zones, the effect of wind stretching the arc should be considered, and then the operating time for which the relay is adjusted has an important bearing on the oute. Tending to offset the longer time an arc has to stretch in the wind when it is in the intermediate or backup zones is the fact that, the farther an arcing fault is from a relay, the less will its effect be on the relay39。 s operation. In other words, the more line impedance there is between the relay and the fault, the less change there will be in the total impedance when the arc resistance is added. On the other hand, the farther away an arc is, the higher its apparent resistance will be because the current contrib。