ABB Relion 670 Series Applications Manual page 343

1MRK 511 358-UUS A
TR1ATCC (90) then compares this voltage with the set voltage,
should be taken. To avoid unnecessary switching around the setpoint, a deadband (degree of
insensitivity) is introduced. The deadband is symmetrical around
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
transformer's tap changer voltage step (typically 75–125% of the tap changer step).
*)
0
ANSI06000489 V2 EN-US
Figure 164: Control actions on a voltage scale
During normal operating conditions the busbar voltage V
(interval between V1 and V2 in figure 164). In that case no actions will be taken by TR1ATCC (90).
However, if V
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
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
A situation where V
When V
B
or rises above
(refer to table 33).
If the busbar voltage rises above
commands (VLOWER commands) in order to bring the voltage back into the security range
(settings
following three ways: off /auto/auto and manual, according to the setting
command, in fast step down mode, is issued with the settable time delay
The measured RMS magnitude of the busbar voltage V
BUSVOLT under Main menu/Test/Function status/Control/
TransformerVoltageControl(ATCC,90)/TR1ATCC:x/TR8ATCC:x.
Time characteristic
The time characteristic defines the time that elapses between the moment when measured
voltage exceeds the deadband interval until the appropriate VRAISE or VLOWER command is
initiated.
Application manual
Security Range
*)
D V
Raise Cmd
Vblock Vmin V
1
*) Action in accordance with setting
becomes smaller than V1, or greater than V2, an appropriate raise or lower timer will
B
. The inner deadband ΔV
in
Vmin and Vmax .
falls outside this range will be regarded as an abnormal situation.
B
Vblock , or alternatively, falls below setting Vmin but still above Vblock ,
falls below setting
Vmax , actions will be taken in accordance with settings for blocking conditions
Vmin , and Vmax ). The fast step down function operation can be set in one of the
Vdeadband should be set to a value near to the power
*)
D
V
Lower Cmd
DV DV
in in
Vset V Vmax
2
VDeadbandInner should be set to a value smaller
, setting
in
Vmax , TR1ATCC (90) can initiate one or more fast step down
is shown on the local HMI as value
B
VSet and decides which action
VSet , see figure 164, and it is
Voltage Magnitude
ANSI06000489-2-en.vsd
, stays within the outer deadband
B
FSDMode . The VLOWER
tFSD .
Section 13
Control
SEMOD159053-82 v5
337