GE D90 Plus Instruction Manual page 570

SERIES COMPENSATED LINES
562
Figure 472: Dynamic reach, low-current external fault
The following figure illustrates a high-current external fault. The air gaps or MOVs conduct
majority of the fault current and neither steady-state nor transient overreach takes place.
The relay does not reduce its reach as it is not necessary.
Figure 473: Dynamic reach, high-current external fault
The following figure illustrates a high-current internal fault. Because of the large current,
the reach is not reduced and the element responds to the internal fault. A traditional
approach would leave this fault out of the relay reach.
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 15: THEORY OF OPERATION