Short Line Application; Long Transmission Line Application - ABB RELION 650 Series Applications Manual

Section 7
Impedance protection
IEC09000248 V2 EN-US
Figure 56: Load encroachment phenomena and shaped load encroachment
[1]
7.1.2.4

Short line application

In short line applications, the major concern is to get sufficient fault resistance coverage. Load
encroachment is not such a common problem. 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 13.
Table 13:
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.
For very short line applications, the underreaching zone 1 can not be used due to the fact that
the voltage drop distribution throughout the line will be too low causing risk for overreaching.
7.1.2.5

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.
What can be recognized as long lines with respect to the performance of distance protection
can generally be described as in table 14. Long lines have Source impedance ratio (SIR's) less
than 0.5.
[1] RLdRv=RLdRvFactor*RLdFw
106
X
Z1
Load impedance
area in forward
direction
characteristic
Definition of short and very short line
Un
110 kV
1.1-5.5 km
5.5-11 km
R
RLdRv
Un
500 kV
5-25 km
25-50 km
1MRK 505 363-UEN A
X
Z1
ArgLd
R
RLdFw
IEC09000248-2-en.vsd
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Application manual