VDeadband, the tap changer of T1 will try to decrease the controlled voltage. In the
opposite case, that is, the voltage is close to the lower limit of VDeadband, the tap
changer at T1 will not try to decrease the controlled voltage. The tap changer for T2
and T3 will not operate due to the fact that the detected 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.
12.1.4 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 504 165-UUS - Section 12
Primary injection testing
Transformer protection RET670 2.2 ANSI 291
Commissioning manual
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