ABB rec670 Commissioning Manual page 200

Section 11
Primary injection testing
194
3. Connect all transformers in the parallel group to the same busbar on the
secondary side.
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 IPRIM is below the overcurrent blocking level (Iblock)
7. Check that the value of ICIRCUL is below the circulating current limit
(CircCurLimit).
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/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
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 UDeadband, 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
UDeadband, 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
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Bay control REC670 2.1 IEC
Commissioning manual