ABB Relion 670 series - Long Transmission Line Application; Parallel Line Application with Mutual Coupling

to-ground fault together with load encroachment algorithm improves the possibility to
detect high resistive faults without conflict with the load impedance, see figure 138.
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
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-ground 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 Vn Vn
110 kV 500 kV
Long lines 45-60 miles 200–250 miles
Very long lines >60 miles >250 miles
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-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).
8.5.2.7 Parallel line application with mutual coupling
General
Introduction of parallel lines in the network is increasing due to difficulties to get
necessary area for new lines.
Parallel lines introduce an error in the measurement due to the mutual coupling between
the parallel lines. The lines need not to be of the same voltage in order to experience
mutual coupling, and some coupling exists even for lines that are separated by 100 meters
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 285
Application manual