ABB REL650 Applications Manual page 206

Section 7
Current protection
200
The basic requirement is to assure selectivity, that is EFPIOC (50N) 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-ground faults and phase-to-phase-
to-ground faults shall be calculated as shown in figure
currents (3I ) to the protection are calculated. For a fault at the remote line end this fault
0
current is I . In this calculation the operational state with high source impedance Z
fB
low source impedance Z
B
is I . In this calculation the operational state with low source impedance Z
fA
source impedance Z should be used.
B
A
Z
~
A
IED
ANSI09000022 V1 EN
Figure 96: Through fault current from A to B: I
A
Z
~
A
IED
Fault
ANSI09000023 V1 EN
Figure 97: 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:
should be used. For the fault at the home busbar this fault current
I
fB
Z
L
Fault
I
fA
Z
L
1MRK 506 334-UUS A
96 and figure 97. The residual
B
Z
~
B
ANSI09000022-1-en.vsd
fB
B
Z
~
B
ANSI09000023-1-en.vsd
fA
Application manual
and
A
and high
A