ABB Relion REB500, Техническое руководство

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max
Ω/ph
2 1.25
V
set
B
U
Z
I

 
where:
• Z
set
is the maximum value of the impedance, that is, the maximum value of the expression:
2 2 2 2
or XA RA XB RB
 
• 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 RLoad. The healthy phases
must be checked for the case of a ground fault.
Current release (low-current check)
GUID-73E85CC0-A645-4715-B6C2-D4A775931D71 v1
For a phase to be included in the phase selection, it must be conducting a current higher than
I
min
. A typical setting is 0.2 I
N
.
Ground fault detector
GUID-052C389C-6C20-4342-BD93-8C51FCC560F8 v1
There are five alternative methods of detecting ground faults; the desired one shall be
selected by the setting of the parameter
GndFaultMode. The neutral current can either be used
on its own or in conjunction with the neutral voltage. The following operating modes are
available:
• I
0
: (I
E
> 3I
0min
) AND (I
E
> 0.25 I
max
)
• I
0
OR U
0
: (I
E
> 3I
0min
) AND (I
E
> 0.25 I
max
) OR (U
E
> 3U
0min
)
• I
0
AND U
0
: (I
E
> 3I
0min
) AND (I
E
> 0.25 I
max
) OR (U
E
> 3 U
0min
)
• I
0
(I
2
): (I
E
> 3I
0min
) AND (I
E
> 0.23 I2)
• I
0
(I
2
) OR U
0
: (I
E
> 3I
0min
) AND (I
E
> 0.23 I2) OR (U
E
> 3U
0min
)
The criterion for the highest
3I0min setting is:
• 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
3I0min setting are:
• 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
3I0min = 0.5 IN.
Section 5 1MRK 505 406-UEN B
Bay protection functions
40 Bay protection functions REB500
Technical manual
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