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Section 9
Current protection
388
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-US
Figure 190:
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-US
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:
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
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 502 071-UUS A
(Equation 193)
= 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
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