ABB RELION RET670, Applications Manual

Page: 379 / 1016

The IED has a built in feature which shapes the characteristic according to the
characteristic shown in figure
176 . The load encroachment algorithm will increase the
possibility to detect high fault resistances, especially for phase-to-ground faults at
remote line end. For example, for a given setting of the load angle
LdAngle , the
resistive blinder for the zone measurement can be set according to figure 176 affording
higher fault resistance coverage without risk for unwanted operation due to load
encroachment. Separate resistive blinder settings are available in forward and reverse
direction.
The use of the load encroachment feature is essential for long heavily 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. Load encroachment is not a major problem. .
R
X
Zm
RldRev
R
Zm
RLdFwd
ZL
ANSI05000495_2_en.vsd
Load impedance area in
forward direction
LdAngle
LdAngle
LdAngle
LdAngle
ANSI05000495 V2 EN-US
Figure 176: Load encroachment phenomena and shaped load encroachment
characteristic
[1]
8.12.2.4 Short line application
GUID-331451C9-EA93-481A-BA2E-D729EDB98828 v4
Transmission line lengths for protection application purposes are classified as short,
medium and long. The definition of short, medium and long lines is found in IEEE Std
C37.113-1999. ). The length classification is defined by the ratio of the source
impedance at the protected line’s terminal to the protected line’s impedance (SIR).
SIR’s of about 4 or greater generally define a short line. Medium lines are those with
SIR’s greater than 0.5 and less than 4
[1] RLdRv=RLdRvFactor*RLdFw
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 373
Application manual