ABB Relion 670 series, Руководство по применению

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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 overreaches. If the currents have the same
direction, the distance protection underreaches.
Maximum overreach occurs if the fault infeed from remote end is weak. If we consider 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 infeed from remote end is zero, we can draw the voltage V in the faulty phase at
A side as in equation 51 .
( )
0 0
p 3 3
= 1 +
A L ph N Nm p
V Z I K I K I
× × + ×
EQUATION1278 V4 EN-US
(Equation 51)
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 52)
Simplification of equation 52 , solving it for 3I0p and substitution of the result into equation 51
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 53)
If we finally divide equation 53 with equation 48 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 54)
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 infeed in the line 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 under-reach scheme.
Parallel line out of service and earthed
SEMOD168232-227 v3 SEMOD168232-229 v3
Section 7 1MRK 505 343-UEN B
Impedance protection
152
Application manual