ABB REL650 - Page 206

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
96 and figure 97. The residual
currents (3I
0
) to the protection are calculated. For a fault at the remote line end this fault
current is I
fB
. In this calculation the operational state with high source impedance Z
A
and
low source impedance Z
B
should be used. For the fault at the home busbar this fault current
is I
fA
. In this calculation the operational state with low source impedance Z
A
and high
source impedance Z
B
should be used.
~
~
Z
A
Z
B
Z
L
A B
IED
I
fB
Fault
ANSI09000022-1-en.vsd
ANSI09000022 V1 EN
Figure 96: Through fault current from A to B: I
fB
ANSI09000023-1-en.vsd
~ ~
Z
A
Z
B
Z
L
A B
IED
I
fA
Fault
ANSI09000023 V1 EN
Figure 97: Through fault current from B to A: I
fA
The function shall not operate for any of the calculated currents to the protection. The
minimum theoretical current setting (Imin) will be:
Section 7 1MRK 506 334-UUS A
Current protection
200
Application manual