ABB REM 54 Series, Technical Reference Manual

Page: 47 / 110

1MRS750915-MUM
REM 54_
47
Machine Terminal
Technical Reference Manual, General
5.1.6.3. Calculated analog channels
The machine terminal includes virtual channels to obtain neutral current and residual
voltage when sensors are used. Current sensors and voltage dividers are connected
to the machine terminal via coaxial cables and therefore a residual connection of
phase currents or an open-delta connection of phase voltages cannot be made. Both
the amplitude and the phase angle are calculated for the virtual channels.
Though primarily meant to be used with sensors, the calculated analog channels can
also be used with conventional current and voltage transformers.
The neutral current I
0
is numerically derived from the three phase currents:
. 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.
The residual voltage U
0
is numerically derived from the three phase voltages:
. U
0S
is used instead of the open-delta connection when
voltage dividers are used to measure phase-to-earth voltages.
If only one virtual channel is used, the channel will be numbered as 11. If both
calculations are used, the I
0S
channel will be given the number 11 and the U
0S
channel the number 12.
5.1.7. Digital inputs
The REM 543 and REM 545 machine terminals differ from each other regarding the
number of digital inputs available.
The digital inputs of the REM 54_ machine terminals are voltage-controlled and
optically isolated. For technical data of the digital inputs, refer to Table 5.2.1-3 on
page 81.
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
).
The events and parameters of I/O cards are included in the event and parameter lists
on the CD-ROM Technical Descriptions of Functions.
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.
I
os
I
L 1
I
L 2
I
L 3
+ +
( )
– =
U
os
U
1
U
2
U
3
+ + ( ) 3 ÷ =