ABB REL670 2.2 IEC - Page 162

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 32)
If we finally divide equation 32 with equation 27 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 33)
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 v3SEMOD168232-229 v3
Z0m
A B
Z< Z<
en05000222.vsd
DOCUMENT11520-IMG867 V1 EN-US
Figure 61: The parallel line is out of service and earthed
When the parallel line is out of service and earthed at both ends on the bus bar side
of the line CT 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 61.
Section 8 1MRK 506 369-UEN B
Impedance protection
156 Line distance protection REL670 2.2 IEC
Application manual