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

The IED's ability 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 without conflict with the load impedance, see figure
112.
For very short line applications, the underreaching zone 1 can not be used due to the
voltage drop distribution throughout the line will be too low causing risk for
overreaching.It is difficult, if not impossible, to apply distance protection for short lines.
It is possible to apply a overreaching pilot communication based POTT or Blocking
scheme protection for such lines to have fast tripping along the entire line. Usually a unit
protection, based on comparison of currents at the ends of the lines is applied for such
lines.
Load encroachment is normally no problems for short line applications.
8.9.2.5 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 well known that it is difficult to
achieve high sensitivity for phase-to-ground fault at remote line end of a long line when
the line is heavy loaded.
What can be recognized as long lines with respect to the performance of distance
protection can generally be described as in table 20, long lines have Source impedance
ratio (SIR’s) less than 0.5.
Table 27: Typical length of long and very 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 IED's ability 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), see figure
112.
8.9.2.6 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.
Section 8 1MRK 506 369-UUS -
Impedance protection
316 Line distance protection REL670 2.2 ANSI
Application manual