Master Follower (Mf) Method - ABB Relion 670 Series Commissioning Manual

Section 12
Primary injection testing
8. Set the control mode to Automatic for all transformers.
9. For transformer T1, adjust the parameter Comp on the local HMI in Main menu/Settings/IED
Settings/Control/TransformerVoltageControl(90, U↕) /TR8ATCC(90, U↕||):x/ParCtrl /Compso
that the LOWER output is activated due to circulating current.
Comp is a setting for circulating current Compensating Factor, and it is effectively a multiplier value
to change the sensitivity of the voltage regulation function to measured values of circulating current.
A nominal value of 200 for Comp should be appropriate to achieve sensitive voltage regulation.
Smaller values may lead to a normal state where tap changers for parallel transformers are well out
of step, and values significantly higher will cause over-sensitivity in the voltage control function and
tap changer hunting behavior. It is an important outcome of the testing process that the
compensating factor is checked for each transformer to ensure sensitive but stable operation for
circulating currents.
For example, if there are three transformers connected in parallel, and the tap changer of
transformer T1 is two steps over the tap changer of T2 and T3, the circulating current detected by
the VCTR for T1 will be the sum (with opposite sign) of the current measured at T2 and T3. The
currents measured at T2 and T3 will ideally be about the same values. If the voltage is close to the
upper limit of the 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 /IED
Settings/Control /TransformerVoltageControl(90, U↕)/TR8ATCC(90, U↕||):x/Voltage/
Umax,Umin .
2. Check that MFMode is set to Follow Tap or Follow Cmd in Main menu/Settings/IED Settings /
Control/TransformerVoltageControl(90, U↕) /TR8ATCC(90, U↕||):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/IED Settings/
Control/TransformerVoltageControl(90, U↕) /TR8ATCC(90, U↕||):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 (90, U↕).
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