ABB RED650, Applications Manual

Page: 123 / 454

One can also 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 40)
Simplification of equation 40 , solving it for 3I0
p
and substitution of the result into
equation 39 gives that the voltage can be drawn as:
U p ZI I K I K
I p
p
A
L ph N Nm
= ⋅ + ⋅ + ⋅
⋅
−






3
3
2
0
0
IECEQUATION1280 V2 EN-US
(Equation 41)
If we finally divide equation 41 with equation 36 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 42)
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-574F8EE5-EAEC-40B8-A615-FDAD2808CD6D v1 GUID-8EB3A8EF-119D-4530-8F01-0879A7478E1F v1
Z
0m
A B
Z< Z<
IEC09000251_1_en.vsd
IEC09000251 V1 EN-US
Figure 57: The parallel line is out of service and earthed
1MRK 505 393-UEN B
Section 7
Impedance protection
Line differential protection RED650 2.2 IEC 117
Application manual