GE D90 Plus Instruction Manual page 661

CHAPTER 15: THEORY OF OPERATION
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 555: 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 556: 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.
SERIES COMPENSATED LINES
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