1MRS755225
Transformer Terminal
Technical Reference Manual, General
RET 54_
41
5.1.6.3.
Calculated analog channels
The RET 54_ transformer terminal includes virtual channels to obtain phase-to-
phase voltages, residual voltage and neutral current. Both the amplitude and the
phase angle arecalculated for the virtual channels.
The virtual channel voltages and currents are numerically derived from the phase
voltages and phase currents according to the Table 5.1.6.3-1. Though primarily
meant to be used with sensors, the calculated analog channels can also be usedwith
conventional current and voltage transformers.
The virtual channels will be numbered according to the priority numbers in the
Table 5.1.6.3-1. The virtual channels used first will be numbered as 11 and the
following as 12, 13 etc. For example, U0s is numbered as 11 and U12s 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.
Table 5.1.6.3-1
Virtual analog channels
1) A minus in front of the parenthesis means, that the default direction of the neutral current is assumed
to be from the line to the busbar, while the normal power flow is from the busbar to the line.
5.1.7.
Digital inputs
The RET 541, RET 543 and RET 545 transformer terminals differ from each other
regarding the number of digital inputs available.
The digital inputs of the RET 54_ transformer terminals are voltage-controlled and
optically isolated. For technical data of the digital inputs, refer to Table 5.2.1-3 on
page 90.
The parameters for input filtering, input inversion and pulse counters (see sections
below) can be set in the Configuration menu under each I/O card (e.g.
Configuration/BIO1/Input filtering
).
Virtual channel
Numeric derivation
Priority number
I
0s
= -(I
L1
+ I
L2
+ I
L3
)
1)
1
I
0bs
= -(I
L1b
+ I
L2b
+ I
L3b
)
1)
2
U
0s
= (U
1
+ U
2
+ U
3
)/3
3
U
0bs
= (U
1b
+ U
2b
+ U
3b
)/3
4
U
12s
= (U
1
- U
2
)
5
U
23s
= (U
2
- U
3
)
6
U
31s
= (U
3
- U
1
)
7
U
12bs
= (U
1b
- U
2b
)
8
U
23bs
= (U
2b
- U
3b
)
9
U
31bs
= (U
3b
- U
1b
)
10
!
