ABB Relion 670 series, Applications Manual

Page: 337 / 760

Where:
Uph is phase to earth voltage at the relay point.
Iph is phase current in the faulty phase.
3I0 is earth fault current.
Z1 is positive sequence impedance.
Z0 is zero sequence impedance.
Z
0m
A B
Z< Z<
IEC09000250_1_en.vsd
IEC09000250 V1 EN-US
Figure 204: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure 205 .
A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN-US
Figure 205: 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 364 .
0 0
0
0 1
1 3 3
3 1 3 1
m L L
ph p
ph L
L L
Z
Z Z
U Z I I I
Z Z
æ ö
-
= × + × +
ç ÷
× ×
è ø
IECEQUATION1276 V3 EN-US
(Equation 364)
By dividing equation 364 by equation 363 and after some simplification we can write the
impedance present to the relay at A side as:
3 0
1 1
3 0
æ ö
×
= +
ç ÷
+ ×
è ø
L
I KNm
Z Z
I ph I KN
EQUATION1277 V3 EN-US
(Equation 365)
Where:
KNm = Z0m/(3 · Z1L)
The second part in the parentheses is the error introduced to the measurement of the line
impedance.
1MRK 505 343-UEN B Section 7
Impedance protection
331
Application manual