ABB RELION RET670, Applications Manual

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8.1.2.5 Long transmission line application
SEMOD168232-128 v3
For long transmission lines the margin to the load impedance that is, to avoid load
encroachment, will normally be a major concern. It is difficult to achieve high
sensitivity for line to ground-fault at remote end of a long lines when the line is heavy
loaded.
Definition of long lines with respect to the performance of distance protection can
generally be described as in table
25 , long lines have SIR’s less than 0.5.
Table 25: Definition of long lines
Line category Vn Vn
110 kV 500 kV
Long lines 45-60 miles 200-250 miles
Very long lines >60 miles >250 miles
The possibility in IED to set resistive and reactive reach independent for positive and
zero sequence fault loops and individual fault resistance settings for phase-to-phase
and phase-to-ground fault together with load encroachment algorithm improves the
possibility to detect high resistive faults at the same time as the security is improved
(risk for unwanted trip due to load encroachment is eliminated), as shown in figure
71 .
Section 8
1MRK 504 163-UUS A
Impedance protection
194 Transformer protection RET670 2.2 ANSI
Application manual