ABB REC670 Applications Manual page 164

Section 8
Current protection
158
GlobalBaseSel: This is used to select GBASVAL function for reference of base
values.
The basic requirement is to assure selectivity, that is EFPIOC shall not be allowed
to operate for faults at other objects than the protected object (line).
For a normal line in a meshed system single phase-to-earth faults and phase-to-
phase-to-earth faults shall be calculated as shown in Figure
residual currents (3I ) to the protection are calculated. For a fault at the remote line
0
end this fault current is I
impedance Z and low source impedance Z
A
home busbar this fault current is I
low source impedance Z
A
Z
~
A
IED
IEC09000022 V1 EN-US
Figure 64: Through fault current from A to B: I
A
Z
~ A
IED
Fault
IEC09000023 V1 EN-US
Figure 65: Through fault current from B to A: I
The function shall not operate for any of the calculated currents to the protection.
The minimum theoretical current setting (Imin) will be:
 

Im in MAX I , I
f A fB
EQUATION284 V2 EN-US
. In this calculation the operational state with high source
fB
should be used. For the fault at the
B
. In this calculation the operational state with
fA
and high source impedance Z
A
I
fB
B
Z
L
Fault
I
fA
B
Z
L
1MRK 511 401-UEN A
64 and Figure 65. The
should be used.
B
Z
~
B
IEC09000022-1-en.vsd
fB
Z
~
B
IEC09000023-1-en.vsd
fA
(Equation 33)
Bay control REC670 2.2 IEC
Application manual