ABB RED670 Handbuch Seite 203

1MRK 505 186-UDE B
Applikationshandbuch
æ ×
3 0 I KNm
= +
Z Z 1
ç
L
+
Iph 3 0 I
è
EQUATION1277 V1 DE
Where:
KNm = Z0m/(3*Z1L)
The second part in the parentheses is the error introduced to the measurement of
the line impedance.
If the current on the parallel line has negative sign compared to the current on the
protected line i.e. the current on the parallel line has an opposite direction
compared to the current on the protected line, the distance function will overreach.
If the currents have the same direction, the distance protection will underreach.
Maximum overreach will occur if the fault infeed from remote end is weak. If we
consider a single line to earth fault at "p" unit of the line length from A to B on the
parallel line for the case when the fault infeed from remote end is zero, we can
draw the voltage V in the faulty phase at A side as in equation 100.
(
= × +
V p Z 1 Iph KN
A L
EQUATION1278 V1 DE
One can also notice that the following relationship exists between the zero
sequence currents:
× = ×
3 I Z 0 3 0 I p Z 0 (2
0 L
EQUATION1279 V1 DE
Simplification of equation 101, solving it for 3I0p and substitution of the result into
equation 100 gives that the voltage can be drawn as:
æ
= × +
V p Z 1 Iph K
ç
A L
è
EQUATION1280 V1 DE
If we finally divide equation
present to the IED as
ö
÷
×
KN
ø
)
× + ×
3 I KNm I 3
0 0 p
-
p )
L
×
3 0 I p
× + ×
3 0 I KN
N m
-
2 p
102 with equation
Abschnitt 4
IED Anwendung
ö
÷
ø
97 we can draw the impedance
(Gleichung 99)
(Gleichung 100)
(Gleichung 101)
(Gleichung 102)
199