ABB Relion 670 Series Applications Manual page 427

1MRK 511 401-UEN Rev. K
selected to a value near the power transformer's tap changer voltage step (typically 75 - 125%
of the tap changer step).
UDeadbandInner : Setting value for one half of the inner deadband, to be set in percent of
UBase . The inner deadband is symmetrical around USet , see section
control for a single
The setting shall be smaller than
25-70% of the
Umax : This setting gives the upper limit of permitted busbar voltage (see section
voltage control for a single
is set to
that only lower commands are permitted.
Umin This setting gives the lower limit of permitted busbar voltage (see section
voltage control for a single
is set to
blocking such that only raise commands are permitted.
Ublock : Voltages below Ublock normally correspond to a disconnected transformer and
therefore it is recommended to block automatic control for this condition (setting
Ublock is set in percent of UBase .
Time
t1Use : Selection of time characteristic (definite or inverse) for t1 .
t1 : Time delay for the initial (first) raise/lower command.
t2Use : Selection of time characteristic (definite or inverse) for t2 .
t2 : Time delay for consecutive raise/lower commands. In the circulating current method, the
second, third, etc. commands are all executed with time delay
transformer in the parallel group that is tapping. In the master-follower method with the
follow tap option, the master is executing the second, third, etc. commands with time delay
The followers on the other hand read the master's tap position, and adapt to that with the
additional time delay given by the setting
tMin : The minimum operate time when inverse time characteristic is used (see section
characteristic", figure 205).
Line voltage drop compensation (LDC)
OpertionLDC : Sets the line voltage drop compensation function On / Off .
OperCapaLDC : This setting, if set On , will permit the load point voltage to be greater than the
busbar voltage when line voltage drop compensation is used. That situation can be caused by
a capacitive load. When the line voltage drop compensation function is used for parallel control
with the reverse reactance method, then
Rline and Xline : For line voltage drop compensation, these settings give the line resistance and
reactance from the station busbar to the load point. The settings for
in primary system ohms. If more than one line is connected to the LV busbar, equivalent
and Xline values should be calculated and given as settings.
When the line voltage drop compensation function is used for parallel control with the reverse
reactance method, then the compensated voltage which is designated "load point voltage" U
is effectively an increase in voltage up into the transformer. To achieve this voltage increase,
Xline must be negative. The sensitivity of the parallel voltage regulation is given by the
magnitude of
control of the busbar voltage. This can be realized in the following way. Figure
vector diagram for a transformer controlled in a parallel group with the reverse reactance
Bay control REC670
Application manual
transformer",figure 204. In that figure
UDeadband value.
transformer", figure 204). It is set in percent of
Auto&ManBlock , then busbar voltages above Umax will result in a partial blocking such
transformer", figure 204). It is set in percent of
Auto Block or Auto&ManBlock , then busbar voltages below Umin will result in a partial
Rline and Xline settings, with Rline being important in order to get a correct
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UDeadband . Typically the inner deadband can be set to
tAutoMSF and set individually for each follower.
OperCapaLDC must always be set On .
"Automatic voltage
UDeadbandInner is equal to DU
UBase . If OVPartBk
"Automatic
UBase . If UVPartBk
t2 independently of which
Rline and Xline are given
206
Section 15
Control
.
in
"Automatic
UVBk ).
t2 .
"Time
Rline
L
shows the
421