circulating current will be half of the current detected at T1. The setting of the
parameter Comp then might need to be increased a little. At least one tap changer
step difference between the different transformers should be allowed in order to
avoid the tap changers to operate too often. If the allowed difference is, for
example, two steps, the tap changer shall be stepped up three steps when setting
the parameter Comp.
10. Set the Comp parameter for T2 and T3 in the same manner as for T1. According
to the described procedure when the tap changer of one transformer is two steps
above the others, it shall automatically step down. When there are only two
transformers in the group either shall one step down or the other step up
depending on the voltage level at the ATCC.
11.1.4 Master Follower (MF) method
The Master Follower method requires a Master to be nominated in a parallel group. It
is responsible for measuring secondary bus voltage and executing commands to raise
and lower tap changers, which are repeated by Follower transformers in the group.
1. Confirm the voltage blocking levels OVPartBK and UVPpartBK in Main
menu/Settings/General settings/Control/
TransformerVoltageControl(ATCC,90)/TR8ATCC:x/Voltage/
Umax,Umin.
2. Check that MFMode is set to Follow Tap or Follow Cmd in Main menu/
Settings/General settings/Control/TransformerVoltageControl(ATCC,
90)/TR8ATCC:x/MFMode.
If this setting is Follow Tap, all Follower transformers shall match the actual tap
setting of the Master, while Follow Cmd requires that Follower transformers
follow the RAISE and LOWER commands executed by the Master.
3. Confirm the maximum difference in tap positions for parallel transformers. The
number of taps is determined by the setting in the Parameter Setting tool under
Main menu/Settings/Setting group N/Control/
TransformerVoltageControl(ATCC,90)/TR8ATCC:x/ParCtrl/
MFPosDiffLim
4. Connect all transformers in the parallel group to the same busbar on both the
primary and secondary sides.
5. Set the control mode to Manual for each transformer in the parallel control group
6. Open the test display for Transformer Voltage Control on the LHMI in Main
menu/Test/Function status/Control/TransformerVoltageControl (ATCC,
90).
1MRK 511 360-UEN A Section 11
Primary injection testing
Bay control REC670 2.1 IEC 195
Commissioning manual
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