ABB Relion REC670 Applications Manual page 143

1MRK 511 358-UEN A
Phase to earth fault
IEC06000654 V1 EN-US
Figure 64: Equivalent of power system for calculation of setting
The residual fault current can be written:
=
3I
0
2 Z
EQUATION1948 V1 EN-US
Where
U
phase
Z
1
Z
0
R
f
The residual voltages in stations A and B can be written:
=
U
0 A
EQUATION1949 V1 EN-US
=
U
OB
EQUATION1950 V1 EN-US
The residual power, measured by the sensitive earth fault protections in A and B will be:
Application manual
Source impedance
Z (pos. seq)
sc
Z (pos. seq)
T,1
R
Z (zero seq)
T,0
U
0A
3I
0
Z
lineAB,1
Z
lineAB,0
U
0B
Z
lineBC,1
Z
lineBC,0
3U
phase
× + + ×
Z 3 R
1 0 f
is the phase voltage in the fault point before the fault
is the total positive sequence impedance to the fault point. Z
is the total zero sequence impedance to the fault point. Z
is the fault resistance.
( )
× +
3I Z 3R
0 T ,0 N
× + +
3I (Z 3R Z
0 T ,0 N lineAB,0
N
Substation A
(pos. seq)
(zero seq)
Substation B
(pos. seq)
(zero seq)
en06000654.vsd
)
= Z +Z +Z +Z
1 sc T,1 lineAB,1 lineBC,1
= Z +3R +Z +Z
0 T,0 N lineAB,0 lineBC,0
Section 7
Current protection
(Equation 51)
(Equation 52)
(Equation 53)
137