CHAPTER 15: THEORY OF OPERATION SERIES COMPENSATED LINES
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 651
Figure 558: Dynamic reach, low-current external fault
The following figure shows a high-current external fault. The air gaps or MOVs conduct the
majority of the fault current and neither steady-state nor transient overreach takes place.
The relay does not reduce its reach because it is not necessary.
Figure 559: Dynamic reach, high-current external fault
The following figure shows 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
leaves this fault out of the relay reach.
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