下面是Glover原文内容 被李元拿掉不少
It becomes diffcult and in some cases impossible to coordinate overcurrent
relays when there are two or more sources at different locations. Consider the
system with two sources shown in Figure 10.22. Suppose there is a fault at
P1. We want B23 and B32 to clear the fault so that service to the three loads
continues without interruption. Using time-delay overcurrent relays, we could
set B23 faster than B21. Now consider a fault at P2 instead. Breaker B23 will
open faster than B21, and load L2 will be disconnected. When a fault can be
fed from both the left and right, overcurrent relays cannot be coordinated.
However, directional relays can be used to overcome this problem.
目前电力系统还没看得很熟 你就先自己看看分析八