Short Line Application; Long Transmission Line Application - ABB RELION 670 Series Applications Manual

Section 7
Impedance protection
could preferably be switched off. See section
encroachment
The settings of the parameters for load encroachment are done in FDPSPDIS function.
IEC09000248 V2 EN-US
Figure 110: Load encroachment phenomena and shaped load encroachment
7.3.2.4

Short line application

In short line applications, the major concern is to get sufficient fault resistance coverage. Load
encroachment is not so common. The line length that can be recognized as a short line is not a
fixed length; it depends on system parameters such as voltage and source impedance, see
table 23.
Table 23:
Line category
Very short line
Short line
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-earth fault
together with load encroachment algorithm improves the possibility to detect high resistive
faults without conflict with the load impedance, see figure 110.
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.
Load encroachment is normally no problem for short line applications.
7.3.2.5

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-earth fault at remote line end of long lines when the line is heavy
loaded.
202
function".
X
Z1
Load impedance
area in forward
direction
characteristic defined in Phase selection with load encroachment function
FDPSPDIS
Definition of short and very short line
Un
110 kV
1.1-5.5 km
5.5-11 km
"Load impedance limitation, without load
R
RLdRv
Un
500 kV
5-25 km
25-50 km
1MRK 504 152-UEN B
X
Z1
ArgLd
R
RLdFw
IEC09000248-2-en.vsd
Application manual
M17048-97 v4
M17048-516 v5