Master Follower (Mf) Method - ABB RET670 Commissioning Manual

Section 11
Primary injection testing
4. Open the test display for Transformer Voltage Control on the LHMI in Main menu/Test/
Function status/Control/TransformerVoltageControl(ATCC,90).
5. Manually execute Raise commands to step up the tap changer for transformer T1 to two
steps above the setting for the other transformers in the parallel group.
6. Check that the value of
7. Check that the value of
8. Set the control mode to
9. For transformer T1, adjust the parameter
Setting group N/Control/TransformerVoltageControl(ATCC,90)/TR8ATCC: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
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
decrease the controlled voltage. In the opposite case, that is, the voltage is close to the lower
limit of
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
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
10. Set 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
General settings/Control/TransformerVoltageControl(ATCC,90)/TR8ATCC:x/Voltage/
Umax,Umin.
2. Check that
settings/Control/TransformerVoltageControl(ATCC,90)/TR8ATCC:x/MFMode.
If this setting is
the Master, while
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
222
IPRIM is below the overcurrent blocking level ( Iblock )
ICIRCUL is below the circulating current limit ( CircCurLimit ).
Automatic for all transformers.
VDeadband , the tap changer at T1 will not try to decrease the controlled voltage. The
Comp parameter for T2 and T3 in the same manner as for T1. According to the
MFMode is set to Follow Tap or Follow Cmd in Main menu/Settings/General
Follow Tap , all Follower transformers shall match the actual tap setting of
Follow Cmd requires that Follower transformers follow the RAISE and
Comp on the local HMI in Main menu/Settings/
Comp should be appropriate to
VDeadband , the tap changer of T1 will try to
Comp .
OVPartBK and UVPpartBK in Main menu/Settings/
1MRK 504 154-UUS B
Comp then
SEMOD176327-244 v3
Commissioning manual