ABB REL650 Applications Manual page 224

Section 7
Current protection
218
Source impedance
Z (pos. seq)
sc
Z (pos. seq)
T,1
Z (zero seq)
T,0
3I
0
Phase to ground fault
ANSI06000654 V1 EN
Figure 109: Equivalent of power system for calculation of setting
The residual fault current can be written:
3V
phase
=
3I
0
× + + ×
2 Z Z 3 R
1 0
EQUATION2023-ANSI V1 EN
Where
V 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:
R
N
V Substation A
0A
Z (pos. seq)
lineAB,1
Z (zero seq)
lineAB,0
V Substation B
0B
Z (pos. seq)
lineBC,1
Z (zero seq)
lineBC,0
en06000654_ansi.vsd
f
1MRK 506 334-UUS A
(Equation 131)
= Z +Z +Z +Z
1 sc T,1 lineAB,1 lineBC,1
= Z +3R +Z +Z
0 T,0 N lineAB,0 lineBC,0
Application manual