ABB RELION 670 SERIES Applications Manual page 340

Section 8
Impedance protection
334
accurately select the proper fault loop in the distance measuring function depending on the
fault type.
The heavy load transfer that is common in many transmission networks may in some cases
be in opposite to the wanted fault resistance coverage. Therefore, the function has a built
in algorithm for load encroachment, which gives the possibility to enlarge the resistive
setting of both the Phase selection with load encroachment and the measuring zones
without interfering with the load.
A current-based phase selection is also included. The measuring elements continuously
measure three phase currents and the residual current and, compare them with the set
values.
The extensive output signals from FRPSPDIS (21) give also important information about
faulty phase(s), which can be used for fault analysis.
Load encroachment
Each of the six measuring loops has its own load (encroachment) characteristic based on
the corresponding loop impedance. The load encroachment functionality is always active,
but can be switched off by selecting a high setting.
The outline of the characteristic is presented in figure 160. As illustrated, the resistive
blinders are set individually in forward and reverse direction while the angle of the sector
is the same in all four quadrants.
1MRK 506 369-UUS -
Line distance protection REL670 2.2 ANSI
Application manual