ABB ret650, Applications Manual

Page: 212 / 392

The use of mean USet is recommended for parallel operation with the circulating
current method, especially in cases when Load Voltage Adjustment is also used.
Line voltage drop compensation for parallel control
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The line voltage drop compensation for a single transformer is described in section
"Line voltage drop" . The same principle is used for parallel control with the
circulating current method and with the master – follower method, except that the
total load current, I
L
, is used in the calculation instead of the individual transformer
current. (See figure 73 for details). The same values for the parameters Rline and
Xline shall be set in all IEDs in the same parallel group. There is no automatic
change of these parameters due to changes in the substation topology, thus they
should be changed manually if needed.
Avoidance of simultaneous tapping
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Avoidance of simultaneous tapping (operation with the circulating current
method)
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For some types of tap changers, especially older designs, an unexpected
interruption of the auxiliary voltage in the middle of a tap manoeuvre, can jam the
tap changer. In order not to expose more than one tap changer at a time,
simultaneous tapping of parallel transformers (regulated with the circulating
current method) can be avoided. This is done by setting parameter
OperSimTap to
On . Simultaneous tapping is then avoided at the same time as tapping actions (in
the long term) are distributed evenly amongst the parallel transformers.
The algorithm in Automatic voltage control for tap changer, parallel control
TR8ATCC will select the transformer with the greatest voltage deviation U
di
to tap
first. That transformer will then start timing, and after time delay t1 the appropriate
URAISE or ULOWER command will be initiated. If now further tapping is
required to bring the busbar voltage inside
UDeadbandInner , the process will be
repeated, and the transformer with the then greatest value of U
di
amongst the
remaining transformers in the group will tap after a further time delay t2 , and so
on. This is made possible as the calculation of I
cc
is cyclically updated with the
most recent measured values. If two transformers have equal magnitude of U
di
then
there is a predetermined order governing which one is going to tap first.
Avoidance of simultaneous tapping (operation with the master follower
method)
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A time delay for the follower in relation to the command given from the master can
be set when the setting
MFMode is Follow Tap that is, when the follower follows
the tap position (with or without an offset) of the master. The setting parameter
tAutoMSF then introduces a time delay on UVRAISE/ULOWER commands
individually for each follower, and effectively this can be used to avoid
simultaneous tapping.
Homing
SEMOD159053-200 v2
Section 11
1MRK 504 169-UEN A
Control
206 Transformer protection RET650 2.2 IEC
Application manual