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1MRK 506 369-UEN B
8.5.2.6
8.5.2.7
Line distance protection REL670 2.2 IEC
Application manual
Table 24:
Definition of short and very short line
Line category
Un
110 kV
Very short line
1.1-5.5 km
Short line
5.5-11 km
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-earth fault together with load encroachment algorithm
improves the possibility to detect high resistive faults without conflict with the load
impedance, see figure 136.
For very short line applications the underreaching zone 1 can not be used due to
that the voltage drop distribution through out the line will be too low causing risk
for overreaching.
Load encroachment is normally no problems for short line applications so the load
encroachment function could be switched off (OperationLdCmp = Off). This will
increase the possibility to detect resistive close-in faults.
Long transmission line application
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 phase-to-earth fault at remote end of a long lines when the line is
heavy loaded.
The definition of long lines with respect to the performance of distance protection
is noted in table 25.
Table 25:
Definition of long lines
Line category
Un
110 kV
Long lines
77 km - 99 km
Very long lines
> 99 km
As mentioned in the previous chapter, 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-earth 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).
Parallel line application with mutual coupling
Impedance protection
Un
500 kV
5-25 km
25-50 km
Un
500 kV
350 km - 450 km
> 450 km
Section 8
SEMOD154680-127 v2
SEMOD154680-148 v1
267
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