![background image](http://html1.mh-extra.com/html/abb/relion-670-series/relion-670-series_applications-manual_3052129281.webp)
(
)
L
ph
N
0
Nm
0p
p Z1 I
K 3I
K
3I
A
U
= ×
+
×
+
×
EQUATION2313 V1 EN-US
(Equation 262)
One can also notice that the following relationship exists between the zero sequence currents:
3
0
3 0
0
2
0
I
Z
I
Z
p
L
p
L
⋅
=
⋅
−
(
)
EQUATION1279 V3 EN-US
(Equation 263)
, solving it for 3I0p and substitution of the result into equation
gives that the voltage can be drawn as:
0
0
3
p
p
3
2
p
1
A
L
ph
N
Nm
I
V
Z
I
K
I
K
×
= ×
+
×
+
×
-
æ
ö
ç
÷
è
ø
EQUATION1280 V2 EN-US
(Equation 264)
If we finally divide equation
with equation
we can draw the impedance present to the
IED as
Z
p ZI
I
KN
I
KN
I
p
p
I
I
KN
L
ph
m
ph
=
⋅
+
⋅
+
⋅
⋅
−
+
⋅
3
3
2
3
0
0
0
EQUATION1379 V3 EN-US
(Equation 265)
Calculation for a 400 kV line, where we for simplicity have excluded the resistance, gives with
X1L=0.303 Ω/km, X0L=0.88 Ω/km, zone 1 reach is set to 90% of the line reactance p=71% that
is, the protection is underreaching with approximately 20%.
The zero sequence mutual coupling can reduce the reach of distance protection on the
protected circuit when the parallel line is in normal operation. The reduction of the reach is
most pronounced with no current infeed in the IED closest to the fault. This reach reduction is
normally less than 15%. But when the reach is reduced at one line end, it is proportionally
increased at the opposite line end. So this 15% reach reduction does not significantly affect
the operation of a permissive underreaching scheme.
Parallel line out of service and earthed
GUID-0242E2DB-A7F8-4D7F-91D1-1C744E3378BF v1
Z
0m
A
B
Z<
Z<
IEC09000251_1_en.vsd
IEC09000251 V1 EN-US
Figure 168: The parallel line is out of service and earthed.
When the parallel line is out of service and earthed at both line ends on the bus bar side of the
line CTs so that zero sequence current can flow on the parallel line, the equivalent zero
sequence circuit of the parallel lines will be according to figure
1MRK 505 343-UEN B
Section 7
Impedance protection
275
Application manual
Содержание Relion 670 series
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