ABB REC670 Applications Manual page 418

Section 14
Control
412
Automatic voltage control for a single transformer
Automatic voltage control for tap changer, single control TR1ATCC (90) measures the
magnitude of the busbar voltage V
voltage drop compensation), this voltage is further used for voltage regulation.
TR1ATCC (90) then compares this voltage with the set voltage, VSet 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
VSet, 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 ΔV. The setting
of ΔV, setting Vdeadband 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 Vblock Vmin
*) Action in accordance with setting
ANSI06000489 V2 EN-US
Figure 170: Control actions on a voltage scale
During normal operating conditions the busbar voltage V
deadband (interval between V1 and V2 in figure 170). In that case no actions will be
taken by TR1ATCC (90). However, if V
V2, 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 (90) will initiate that the appropriate VLOWER
or VRAISE 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 the
inner deadband is denoted ΔV
should be set to a value smaller than ΔV. It is recommended to set the inner deadband
to 25-70% of the ΔV value.
This way of working is used by TR1ATCC (90) while the busbar voltage is within the
security range defined by settings Vmin and Vmax.
A situation where V falls outside this range will be regarded as an abnormal situation.
B
. If no other additional features are enabled (line
B
Security Range
D V D
V
Lower Cmd
DV DV
in in
V Vset V Vmax
1 2
becomes smaller than V1, or greater than
B
. The inner deadband ΔV
in
1MRK 511 401-UUS A
SEMOD159053-73 v6
*)
Voltage Magnitude
ANSI06000489-2-en.vsd
, stays within the outer
B
, setting VDeadbandInner
in
Bay control REC670 2.2 ANSI
Application manual