ABB REF 54 Series, Техническое справочное руководство, общее

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1MRS750527-MUM Feeder Terminal
Technical Reference Manual, General
REF 54_
5.1.6.3. Calculated analog channels
The REF 54_ feeder terminal includes virtual channels to obtain phase-to-phase
voltages, residual voltage and neutral current when sensors are used. Current sensors
and voltage dividers are connected to the feeder terminal via coaxial cables.
Therefore a phase-to-phase voltage connection, an open-delta connection of phase
voltages or a residual connection of phase currents cannot be made. Both the
amplitude and the phase angle are calculated for the virtual channels.
The virtual channel voltages and currents are numerically derived from the phase
voltages and phase currents according to Table . Though primarily meant to be used
with sensors, the calculated analog channels can also be used with conventional
current and voltage transformers.
The virtual channels will be numbered according to the priority numbers in Table .
The virtual channels used first will be numbered as 11 and the following as 12, 13
and so on. For example, U
0s
is numbered as 11 and U
12s
as 12, if these virtual
channels are selected for use.
1) A minus in front of the parenthesis means, that the default direction of neutral current is assumed to
be from the line to the busbar, while the normal power flow is from the busbar to the line.
2) This virtual channel is supported in the feeder terminal revisions of Release 2.5 or later, refer to the
section “Revision identification” on page 105.
When sensitive earth-fault protection is needed, core balance
transformers are not recommended to be replaced with the
numerically derived sum of phase currents. Normally, an earth-fault
setting below 10% of the rated value requires the use of a core
balance transformer.
Table 5.1.6.3-1 Virtual analog channels
Virtual channel Numeric derivation Priority number
I
0s
= -(I
L1
+ I
L2
+ I
L3
)
1) 1
I
0bs
2)
= -(I
L1b
+ I
L2b
+ I
L3b
)
1) 2
U
0s
= (U
1
+ U
2
+ U
3
)/3 3
U
0bs
2) = (U
1b
+ U
2b
+ U
3b
)/3 4
U
12s
2) = (U
1
- U
2
) 5
U
23s
2)
= (U
2
- U
3
) 6
U
31s
2) = (U
3
- U
1
) 7
U
12bs
2) = (U
1b
- U
2b
) 8
U
23bs
2) = (U
2b
- U
3b
) 9
U
31bs
2) = (U
3b
- U
1b
) 10