ABB RELION 650 Series Applications Manual page 116

Section 7
Impedance protection
Simplification of equation 43, solving it for 3I0
gives that the voltage can be drawn as:
U = ⋅ p ZI
A
IECEQUATION1280 V2 EN-US
If we finally divide equation
as
Z = ⋅ p ZI
EQUATION1379 V3 EN-US
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
A
Z<
IEC09000251 V1 EN-US
Figure 59: 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 60.
I
A
B
IEC09000252 V1 EN-US
Figure 60: Equivalent zero sequence impedance circuit for the double-circuit line that
Here the equivalent zero-sequence impedance is equal to Z
Z +Z
0m 0m
110

I + K ⋅ 3 I +

L ph N 0

44

I + KN ⋅ 3 I + KN

ph 0

L

I + 3 I KN
ph 0


B
Z
0m
Z<
IEC09000251_1_en.vsd
-
Z Z
0 0m
0
Z
0m
-
Z
Z
0 0m
IEC09000252_1_en.vsd
operates with one circuit disconnected and earthed at both ends
which is equal to equation 46.
and substitution of the result into equation
p

3 I ⋅ p
0
K ⋅

Nm
2 − p

with equation 39 we can draw the impedance present to the IED

3 I ⋅ p
0
⋅

m
2 − p


⋅


I
0
C
1MRK 505 363-UEN A
GUID-574F8EE5-EAEC-40B8-A615-FDAD2808CD6D v1 GUID-8EB3A8EF-119D-4530-8F01-0879A7478E1F v1
-Z m in parallel with (Z
0 0
Application manual
42
(Equation 44)
(Equation 45)
-Z )/Z -
0 0m 0