ABB Relion REC670 Applications Manual page 305

1MRK 511 358-UEN A
Measured Quantities
In normal applications, the LV side of the transformer is used as the voltage measuring point.
If necessary, the LV side current is used as load current to calculate the line-voltage drop to the
regulation point.
Automatic voltage control for tap changer, TR1ATCC for single control and TR8ATCC for
parallel control function block has three inputs I3P1, I3P2 and U3P2 corresponding to HV-
current, LV-current and LV-voltage respectively. These analog quantities are fed to the IED via
the transformer input module, the Analog to Digital Converter and thereafter a Pre-Processing
Block. In the Pre-Processing Block, a great number of quantities for example, phase-to-phase
analog values, sequence values, max value in a three phase group etc., are derived. The
different function blocks in the IED are then "subscribing" on selected quantities from the pre-
processing blocks. In case of TR1ATCC or TR8ATCC, there are the following possibilities:
• I3P1 represents a three-phase group of phase current with the highest current in any of
the three phases considered. As only the highest of the phase current is considered, it is
also possible to use one single-phase current as well as two-phase currents. In these
cases, the currents that are not used will be zero.
• For I3P2 and U3P2 the setting alternatives are: any individual phase current/voltage, as
well as any combination of phase-phase current/voltage or the positive sequence current/
voltage. Thus, single-phase as well as, phase-phase or three-phase feeding on the LV-side
is possible but it is commonly selected for current and voltage.
High Voltage Side
(Load Current) I
Low Voltage Side
IEC10000044 V2 EN-US
Figure 150: Signal flow for a single transformer with voltage control
On the HV side, the three-phase current is normally required in order to feed the three-phase
over current protection that blocks the load tap changer in case of over-current above harmful
levels.
The voltage measurement on the LV-side can be made single phase-earth. However, it shall be
remembered that this can only be used in solidly earthed systems, as the measured phase-
Application manual
I ,I ,I
L1 L2 L3
p r
e
a
g
T
n
d
a
a
h
o
C
L
L
3ph or ph-ph or 1ph Current
3ph or ph-ph or 1ph Voltage
Line Impedance R+jX
Load Center
raise,lower
BOM
signals/alarms
position
MIM
TRM
U (Busbar Voltage)
B
UL (Load Point Voltage)
IEC10000044-2-en.vsd
Section 13
SEMOD159053-61 v4
SEMOD159053-65 v6
IED
BIM
Control
299