ABB Relion 670 Series Applications Manual page 374

Section 14
Control
Parallel control with the master-follower method
In the master-follower method, one of the transformers is selected to be master, and will regulate
the voltage in accordance with the principles for Automatic voltage control. Selection of the
master is made by activating the binary input FORCMAST in TR8ATCC (90) function block for one
of the transformers in the group.
The followers can act in two alternative ways depending on the setting of the parameter
When this setting is
the master, will initiate the corresponding command in all follower TR8ATCCs (90) simultaneously,
and consequently they will blindly follow the master irrespective of their individual tap positions.
Effectively this means that if the tap positions of the followers were harmonized with the master
from the beginning, they would stay like that as long as all transformers in the parallel group
continue to participate in the parallel control. On the other hand for example, one transformer is
disconnected from the group and misses a one tap step operation, and thereafter is reconnected
to the group again, it will thereafter participate in the regulation but with a one tap position
offset.
If the parameter
master and adopt to the same tap position or to a tap position with an offset relative to the
master, and given by setting parameter
setting parameter
for each follower when setting
Selecting a master is made by activating the input FORCMAST in TR8ATCC (90) function block.
Deselecting a master is made by activating the input RSTMAST. These two inputs are pulse
activated, and the most recent activation is valid that is, an activation of any of these two inputs
overrides previous activations. If none of these inputs has been activated, the default is that the
transformer acts as a follower (given of course that the settings are parallel control with the
master follower method).
When the selection of master or follower in parallel control, or automatic control in single mode, is
made with a three position switch in the substation, an arrangement as in figure
arranged with application configuration.
Figure 178: Principle for a three-position switch Master/Follower/Single
Parallel control with the reverse reactance method
Consider Figure
The tap positions will diverge and finally end up in a runaway tap situation if no measures to avoid
this are taken.
368
Follow Cmd , raise and lower commands (VRAISE and VLOWER) generated by
MFMode is set to Follow Tap , then the followers will read the tap position of the
TapPosOffs (positive or negative integer value). The
tAutoMSF introduces a time delay on VRAISE/VLOWER commands individually
MFMode has the value Follow Tap .
179 with two parallel transformers with equal rated data and similar tap changers.
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1MRK 511 401-UUS F
SEMOD159053-140 v5
MFMode .
178 below is
SEMOD159053-145 v4
Bay control REC670
Application manual