• T1RXOP and T2RXOP shall be set to On in instance 3 of TR8ATCC
• T2RXOP and T3RXOP shall be set to On in instance 1 of TR8ATCC
and so on.
The parameter corresponding to the own IED must not be set.
T1RXOP should thus not be set in IED T1, T2RXOP not in
IED T2, and so on.
6. Set the parallel operation (OperationPAR) to Off.
7.
Set the control mode, for each transformer in the parallel control group, to
Manual in the local HMI for that IED.
8. Undertaking switching operations to connect all transformers to the same bus
on the secondary side.
9. Manually execute RAISE commands from the local HMI to step up the tap
changer for transformer T1, two steps above the setting for the other
transformers in the parallel group.
10. Change the setting of USet in each of the remaining transformers to
correspond to the manually set busbar voltage being measured by T1, which
can be located on the local HMI under Main menu/Control/Command/
TansformerVoltageControl(ATCC,90)/VCSx/VCPx
11. Set in all the parallel connected transformers the parameter OperationPAR to
CC.
12. On the lcoal HMI, set the control mode to Automatic for all transformers.
13. For transformer T1 adjust the parameter Comp in the local HMI under Main
menu/Settings/Setting group N/Control/
TransformerVoltageControl(ATCC,90)/VCPx/ParCtrl/Comp so that the
LOWER output is activated due to circulating current, based on guidelines
below.
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. Values
less 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.
Example of Comp behavior
If there are three transformers connected in parallel, and the
tap changer of transformer T1 lies 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
1MRK 504 088-UEN C Section 14
Primary injection testing
209
Installation and commissioning manual
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