外文翻译--变压器的类型及结构(编辑修改稿)

外文翻译--变压器的类型及结构(编辑修改稿)内容摘要：

on the line terminals of breaker tripping should be faster than B, however , the condition reverses and B should be faster than D. It is evident that the relay protection engineer must find some characteristic other than time delay if relay coordination is to be achieved． 3 The magnitude 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 an。