ABB REL650 series, Applications Manual

Page: 124 / 516

a A B
A L f
A A
V I I
Z p Z R
I I
+
= = × + ×
EQUATION1274 V2 EN
(Equation 42)
The infeed factor (I
A
+I
B
)/I
A
can be very high, 10-20 depending on the differences in
source impedances at local and remote end.
21
ZL
21
Es
A
V
A
VA
A
B
Es
B
I
A
I
B
R
f
p*ZL
(1-p)*ZL
Z
SA
Z
SB
en05000217_ansi.vsd
ANSI05000217 V1 EN
Figure 52: Influence of fault current infeed from remote line end
The effect of fault current infeed from remote line end is one of the most driving factors
for justify complementary protection to distance protection.
When the line is heavily loaded, the distance protection at the exporting end will have a
tendency to overreach. To handle this phenomenon, the IED has an adaptive built-in
algorithm, which compensates the overreach tendency of zone 1, at the exporting end. No
settings are required for this function.
6.1.2.3 Short line application
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.
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
7 .
Section 6
1MRK 506 334-UUS A
Impedance protection
118
Application manual