ABB REC670 Applications Manual page 191

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
Source impedance
Z (pos. seq)
sc
Z (pos. seq)
T,1
Z (zero seq)
T,0
3I
0
Phase to earth fault
IEC06000654 V1 EN-US
Figure 80: Equivalent of power system for calculation of setting
The residual fault current can be written:
3U
=
phase
3I
0
× + + ×
2 Z Z 3 R
1 0 f
EQUATION1948 V1 EN-US
Where
U is the phase voltage in the fault point before the fault
phase
Z is the total positive sequence impedance to the fault point. Z
1
Z is the total zero sequence impedance to the fault point. Z
0
R is the fault resistance.
f
The residual voltages in stations A and B can be written:
(
= × +
U 3I Z 3R
0 A 0 T ,0 N
EQUATION1949 V1 EN-US
= × +
U 3I (Z 3R
OB 0 T ,0 N
EQUATION1950 V1 EN-US
R
N
U Substation A
0A
Z (pos. seq)
lineAB,1
Z (zero seq)
lineAB,0
U Substation B
0B
Z (pos. seq)
lineBC,1
Z (zero seq)
lineBC,0
en06000654.vsd
)
+
Z )
lineAB,0
Section 8
Current protection
(Equation 51)
= Z +Z +Z +Z
1 sc T,1 lineAB,1 lineBC,1
= Z +3R +Z +Z
0 T,0 N lineAB,0 lineBC,0
(Equation 52)
(Equation 53)
185