according to the expected maximum load since these settings are used internally in the
function as reference points to improve the performance of the phase selection.
R
X
Z1
Load impedance
area in forward
direction
RLdRv
R
Z1
ArgLd
RLdFw
IEC09000248-2-en.vsd
X
IEC09000248 V2 EN-US
Figure 202: Load encroachment phenomena and shaped load encroachment
characteristic
7.13.2.4
Short line application
GUID-7FA1B585-C979-4D51-A502-9C4070B99F0E v2
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
Table 29: Definition of short and very short line
Line category
Un
Un
110 kV
500 kV
Very short line
1.1-5.5 km
5-25 km
Short line
5.5-11 km
25-50 km
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
.
For very short line applications, the underreaching zone 1 cannot 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.
7.13.2.5
Long transmission line application
GUID-AD1A1A5B-B4F5-4B48-9DBD-59D28D71BA9C v2
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.
What can be recognized as long lines with respect to the performance of distance protection
can generally be described as in table
, long lines have Source impedance ratio (SIR’s) less
than 0.5.
Section 7
1MRK 505 343-UEN B
Impedance protection
328
Application manual
Содержание Relion 670 series
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