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1MRK 506 369-UEN B
Line distance protection REL670 2.2 IEC
Application manual
-
Z
Z
0
0m
A
-
Z
Z
0
0m
B
IEC09000253 V1 EN-US
Figure 174:
Equivalent zero sequence impedance circuit of the double-circuit,
parallel, operating line with a single phase-to-earth fault at the
remote busbar
When mutual coupling is introduced, the voltage at the relay point A will be
changed according to equation 295.
æ
Z
0
=
×
+
×
U
Z
1
I
3
I
ç
ph
0
ph
L
3
è
IECEQUATION1276 V3 EN-US
By dividing equation
295
write the impedance present to the relay at A side as:
æ
×
3 0
I
KNm
=
+
Z
Z
1 1
ç
L
+
I ph
3 0
I
è
EQUATION1277 V3 EN-US
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, that is, 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 current infeed from remote line end is
weak. If considering a single phase-to-earth fault at 'p' unit of the line length from
A to B on the parallel line for the case when the fault current infeed from remote
line end is zero, the voltage U
(
U
= ⋅
p ZI
I
+
K
A
L
ph
N
IECEQUATION1278 V2 EN-US
Z
0m
IEC09000253_1_en.vsd
ö
-
Z
0
Z
1
+
m
L
L
3
I
÷
0
p
×
×
Z
1
3
Z
1
ø
L
L
by equation
294
and after some simplification we can
ö
÷
×
KN
ø
in the faulty phase at A side as in equation 297.
A
)
⋅
3
I
+
K
⋅
3
I
0
Nm
0
p
Section 8
Impedance protection
C
(Equation 295)
(Equation 296)
(Equation 297)
341
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