ABB Relion 670 series - Page 240

A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN
Figure 115: Equivalent zero sequence impedance circuit of the double-circuit,
parallel, operating line with a single phase-to-ground fault at the remote
busbar
When mutual coupling is introduced, the voltage at the relay point A will be changed
according to equation
113.
0 0
0
0 1
1 3 3
3 1 3 1
m
L L
ph p
ph L
L L
Z
Z Z
V Z I I I
Z Z
æ ö
-
= × + × +
ç ÷
× ×
è ø
EQUATION1276 V4 EN (Equation 113)
By dividing equation 113 by equation 112 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 (Equation 114)
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-ground 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 V
A
in the faulty phase at A side as in equation
115.
Section 8 1MRK 506 369-UUS -
Impedance protection
234 Line distance protection REL670 2.2 ANSI
Application manual