外文翻譯--變壓器的類型及結構-全文預覽
【正文】 of the fault current through breakers B and D is the same， regardless of the location of the fault on the line terminal of breaker B or D． Therefore relay coordination must be based on characteristics other than a time delay that starts from the time of the fault. Observe that the direction of current flowing through either breaker B or D is a function of which line the fault is on. Thus for a fault on the line between A and B, the current flows out of the load bus through breaker B toward the fault． At breaker D the current flows toward the load bus through breaker D． In this case breaker B should trip, but breaker D should not trip． This can be acplished by installing directional relays on breakers B and D that are connected in such a way that they will trip only when current flows through them in a direction away from the load bus. Relay coordination for the system shown in Fig． 1l can now be achieved by the installation of directional over current time delay relays on breakers B and D． Breakers A and C can have non directional over current time delay relays． They may also now have instantaneous relays applied． The relays would be set as follows：The directional relays could be set with no intentional time delay. They will have inherent time delay． The time delay over current relays on breakers A and C would have current settings that would permit them to supply backup protection for faults on the load bus and load equipment faults． The instantaneous elements on breakers A and C would have current settings that would not permit them to detect faults on the load bus． Thus the lines between the generator and the load would have highspeed protection over a considerable portion of their length． It should be observed that faults on the line terminals of breakers A and C can co11apse the generator vo1tage． The instantaneous relays on breakers A or C cannot clear the circuit instantaneously， because it takes time for power equipment to operate． During this period there will be little or no current flow through breakers B and D． Therefore， B or D c
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