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1MRK 504 165-UEN Rev. K
of transformers are defined by setting TnRXOP to On or Off. The following rules are applicable for
the settings of T1RXOP – T8RXOP.
•
In each instance of TR8ATCC, set all TnRXOP parameters corresponding to the connected
IEDs to On except the parameter corresponding to the IED itself. For example, do not set
T1RXOP to On in IED T1 or T2RXOP to On in IED T2.
For example, if IEDs T1, T2 and T3 are connected,
•
In instance 1 of TR8ATCC, set T2RXOP and T3RXOP to On.
•
In instance 2 of TR8ATCC, set T1RXOP and T3RXOP to On.
•
In instance 3 of TR8ATCC, set T1RXOP and T2RXOP to On.
12.1.3
Minimum Circulating Current (MCC) method
Voltage control of parallel transformers with the circulating current method means minimizing the
circulating current at a given voltage target value. The busbar voltage (UB) is measured individually
for each transformer in the parallel group by its associated TR8ATCC function. These measured
values are then exchanged between the transformers, and in each TR8ATCC block, the mean value
of all UB values is calculated. The resulting value UBmean is then used in each IED instead of UB for
the voltage regulation.
1.
Check the overcurrent blocking level (Iblock) in Main menu /Settings/IED Settings /Control/
TransformerVoltageControl(90, U↕) /TR8ATCC(90, U↕||):x/TCCtrl/Iblock.
2.
Check that the circulating current blocking (OperCCBlock) is set On, and the check the correct
settings for circulating current limit (CircCurLimit) in Main menu/Settings /IED Settings/
Control /TransformerVoltageControl(90, U↕)/TR8ATCC(90, U↕||):x/ParCtrl/CircCurrLimit .
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(90, U↕) .
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/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
Transformer protection RET670
Commissioning manual
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IEC13000252-1-en.vsd
Section 12
Primary injection testing
SEMOD176327-195 v5
281
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