ABB RELION REX640 - Page 1737

Y G j Basymm asymm asymm= + ⋅
(Equation 387)
(only connected in phase A)
• The single-phase earth fault in the network is presented with admittance Y
f
= G
f
+ j · B
f
. Fault impedance can be assumed to be purely resistive (fault resistance
R
f
) which is connected between phase A, B or C and earth depending on the
faulted phase.
• The zero-sequence impedance of the earthing (or main) transformer with the
neutral point connected to the coil is represented with impedance Z
oTr
(in the
three-phase equivalent scheme one third must be applied).
E
A
E
B
E
C
Icoil
U
0
U
0coil
Z
oTr
3
I
A
I
B
I
C
Y
d
U
A
U
B
U
C
A
B
C
Y
f
I
f
Y
A
= Y
symm
/3 + Y
asymm
Y
B
= Y
symm
/3 Y
C
= Y
symm
/3
Y
coil
BUSBAR
Figure 926: Simplified three-phase equivalent circuit of a compensated distribution
network
E
A
Phase A to earth voltage of the source
E
B
Phase B to earth voltage of the source
E
C
Phase C to earth voltage of the source
U
A
Phase A to earth voltage at busbar (= E
A
+ U
o
)
U
B
Phase B to earth voltage at busbar (= E
B
+ U
o
)
U
C
Phase C to earth voltage at busbar (= E
C
+ U
o
)
U
0
Zero-sequence voltage = (U
A
+ U
B
+U
C
)/3
U
0coil
Zero-sequence voltage measured at coil
I
A
Phase A current at the source
I
B
Phase B current at the source
I
C
Phase C current at the source
I
coil
Current through the central compensation coil
Y
A
Phase A to earth admittance of the network
Y
B
Phase B to earth admittance of the network
Y
C
Phase C to earth admittance of the network
Y
coil
Admittance of central compensation coil including the parallel resistor
Z
oTr
Zero-sequence impedance of the earthing transformer or the main transform-
er through which the coil is connected to the network. Settings R0Transformer
1MRS759142 F Control functions
REX640
Technical Manual
1737