ABB REC670 Applications Manual page 389

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
systems, as the measured phase-earth voltage can increase with as much as a factor
√3 in case of earth faults in a non-solidly earthed system.
The analog input signals are normally common with other functions in the IED for
example, protection functions.
The LV-busbar voltage is designated U
load point voltage U
Automatic voltage control for a single transformer
Automatic voltage control for tap changer, single control TR1ATCC measures the
magnitude of the busbar voltage U
(line voltage drop compensation), this voltage is further used for voltage
regulation.
TR1ATCC then compares this voltage with the set voltage, USet and decides which
action should be taken. To avoid unnecessary switching around the setpoint, a
deadband (degree of insensitivity) is introduced. The deadband is symmetrical
around USet, see figure 170, and it is arranged in such a way that there is an outer
and an inner deadband. Measured voltages outside the outer deadband start the
timer to initiate tap commands, whilst the sequence resets when the measured
voltage is once again back inside the inner deadband. One half of the outer
deadband is denoted ΔU. The setting of ΔU, setting Udeadband should be set to a
value near to the power transformer's tap changer voltage step (typically 75–125%
of the tap changer step).
*) *)
Raise Cmd
0 Ublock Umin
*) Action in accordance with setting
IEC06000489 V2 EN-US
Figure 170: Control actions on a voltage scale
During normal operating conditions the busbar voltage U
deadband (interval between U1 and U2 in figure 170). In that case no actions will
be taken by TR1ATCC. However, if U
U2, an appropriate raise or lower timer will start. The timer will run as long as the
measured voltage stays outside the inner deadband. If this condition persists longer
than the preset time delay, TR1ATCC will initiate that the appropriate ULOWER
or URAISE command will be sent from TCMYLTC or TCLYLTC function block
to the transformer tap changer. If necessary, the procedure will be repeated until the
magnitude of the busbar voltage again falls within the inner deadband. One half of
.
L
. If no other additional features are enabled
B
Security Range
D U D
U
Lower Cmd
DU DU
in
in
U Uset U Umax
2
1
becomes smaller than U1, or greater than
B
Section 14
Control
, the load current I and
B L
SEMOD159053-73 v6
*)
Voltage Magnitude
IEC06000489_2_en.vsd
, stays within the outer
B
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