ABB REG670 Applications Manual page 229

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
One can also notice that the following relationship exists between the zero sequence
currents:
3 ⋅ 0 = 3 0 ⋅ 0 2
I Z I Z
0 L p L
EQUATION1279 V3 EN
Simplification of equation 45, solving it for 3I0
equation 44 gives that the voltage can be drawn as:

= ⋅ +
U p ZI I K

A
L ph N

IECEQUATION1280 V2 EN
If we finally divide equation
to the IED as

I + KN

ph

Z = ⋅ p ZI
L

I
ph


EQUATION1379 V3 EN
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
0m
Z< Z<
IEC09000251_1_en.vsd
IEC09000251 V1 EN
Figure 101: 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 87.
( )
−
p

3 I ⋅ p
0
⋅ 3 + ⋅
I K

0 Nm
2 − p

46 with equation 41

3 I ⋅ p
0
⋅ 3 I + KN ⋅

0 m
2 − p


+ 3 I KN ⋅
0


B
Section 8
Impedance protection
and substitution of the result into
p
we can draw the impedance present
(Equation 91)
(Equation 92)
(Equation 93)
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