ABB RELION REB500 Technical Manual page 46

Section 5
Bay protection functions
Z
where:
• Z
set
• U is the lowest phase voltage of the healthy phases for aground fault on one phase (U =
0.85 × min. system voltage). The factor 0.85 takes account of a negligibly small zero-
sequence source impedance.
• Uv is the lowest phase-to-phase system voltage.
• 1.25 is the safety factor
• 2 is the factor, which takes account of the fact that phase currents and not phase-to-
phase currents are used.
These requirements are generally fulfilled for most applications. If the first inequality is not
satisfied, the right-hand side must be expressed vectorially and compared with the
underimpedance starting characteristic in relation to the setting
must be checked for the case of a ground fault.
Current release (low-current check)
For a phase to be included in the phase selection, it must be conducting a current higher than
I . A typical setting is 0.2 I
min
Ground fault detector
There are five alternative methods of detecting ground faults; the desired one shall be
selected by the setting of the parameter
on its own or in conjunction with the neutral voltage. The following operating modes are
available:
• I : (I
0
• I OR U
0
• I AND U
0
• I (I
0
• I (I
0
The criterion for the highest
• The ground fault detector must pick up for all ground faults within the reach of the
underimpedance starters in solidly grounded power systems and all cross-country faults
in ungrounded or impedance grounded power systems.
The criteria for the lowest
• The ground fault detector must not pick up for a ground fault on ungrounded systems or
systems with Petersen coils
• The ground fault detector must not pick up for phase faults, although CT errors can cause
false neutral currents.
The recommended setting is
40
U

V
2   1.25
set
I
max
B
is the maximum value of the impedance, that is, the maximum value of the expression:

2 2
XA RA or XB
.
N
> 3I ) AND (I > 0.25 I
E 0min E
: (I > 3I ) AND (I
0 E 0min
: (I > 3I ) AND (I
0 E 0min
): (I > 3I ) AND (I > 0.23 I2)
2 E 0min E
) OR U : (I > 3I ) AND (I
2 0 E 0min
3I0min setting is:
3I0min setting are:
3I0min = 0.5 IN.
© Copyright 2019 ABB. All rights reserved
Ω/ph

2 2
RB
GndFaultMode . The neutral current can either be used
)
max
> 0.25 I ) OR (U > 3U
E max E
> 0.25 I ) OR (U > 3 U
E max E
> 0.23 I2) OR (U > 3U
E E
RLoad . The healthy phases
GUID-73E85CC0-A645-4715-B6C2-D4A775931D71 v1
GUID-052C389C-6C20-4342-BD93-8C51FCC560F8 v1
)
0min
)
0min
)
0min
Bay protection functions REB500
1MRK 505 406-UEN B
Technical manual