ABB REL650 series, Applications Manual

Page: 135 / 516

to load encroachment. The part of the load encroachment sector that comes inside the mho
circle will not cause a trip if FMPSPDIS (21) is activated for the zone measurement. This
is valid in both directions.
R
X
RLd
RLd
LdAngle
LdAngle
LdAngle
LdAngle
en06000404_ansi.vsd
ANSI06000404 V1 EN
Figure 63: Load encroachment of Faulty phase identification with load
encroachment for mho function FMPSPDIS (21) characteristic
The use of the load encroachment feature is essential for long heavy loaded lines, where
there might be a conflict between the necessary emergency load transfer and necessary
sensitivity of the distance protection. The function can also preferably be used on heavy
loaded medium long lines. For short lines the major concern is to get sufficient fault
resistance coverage and load encroachment is not a major problem.
6.1.3 Setting guidelines
6.1.3.1 General
The settings for Five zone distance protection, quadrilateral and mho characteristic
function (ZQMPDIS, 21) are done in primary values. The instrument transformer ratio
that has been set for the analog input card is used to automatically convert the measured
secondary input signals to primary values used in ZQMPDIS(21).
1MRK 506 334-UUS A
Section 6
Impedance protection
129
Application manual