ABB REL670 2.2 IEC - Long Transmission Line Application

Table 24: Definition of short and very short line
Line category Un Un
110 kV 500 kV
Very short line
Short line
1.1-5.5 km 5-25 km
5.5-11 km 25-50 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.
8.5.2.6 Long transmission line application
SEMOD154680-127 v2
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 Un
110 kV 500 kV
Long lines 77 km - 99 km 350 km - 450 km
Very long lines > 99 km > 450 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).
8.5.2.7 Parallel line application with mutual coupling
SEMOD154680-148 v1
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 267
Application manual