ABB REL670 2.2 IEC, Applications Manual

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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 241)
If we finally divide equation 241 with equation 236 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 242)
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 current infeed in the 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
underreaching scheme.
Parallel line out of service and earthed
GUID-0242E2DB-A7F8-4D7F-91D1-1C744E3378BF v1
Z
0m
A B
Z< Z<
IEC09000251_1_en.vsd
IEC09000251 V1 EN-US
Figure 152: The parallel line is out of service and earthed.
When the parallel line is out of service and earthed at both line ends on the bus bar
side of the line CTs 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
153 .
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 301
Application manual