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Technical Reference Manual, General
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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 and
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 the table 4.1.6.3.-1. Though primarily
meant to be used with sensors, the calculated analogue channels can also be used
with conventional current and voltage transformers.
The virtual channels will be numbered according to the priority numbers in the table
4.1.6.3.-1. The virtual channels used first will be numbered as 11 and the following
as 12, 13 etc. For example, U
0s
is numbered as 11 and U
12s
as 12, if these virtual
channels are selected for use.
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.
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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 the Release 2.5 or later, refer to
the section “Revision identification” on page 90.
Amplitude error at the whole measuring range
(e = error in per cent)
Amplitude correction factor
= 1 / ( 1+ e/100 )
Phase displacement error at the whole measuring
range (e = error in degrees)
Phase displacement error = - e
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I
0s
= -(I
L1
+ I
L2
+ I
L1
)
1)
1
I
0bs
2)
= -(I
L1b
+ I
L2b
+ I
L1b
)
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
!
