Voltage Control Of Parallel Transformers; Minimum Circulating Current (Mcc) Method - ABB RET670 Commissioning Manual

1MRK 504 165-UEN A
12.1.2
12.1.3
Transformer protection RET670 2.2 IEC
Commissioning manual

Voltage control of Parallel Transformers

In parallel operation, each transformer protection IED must be connected to the
station communication bus for data exchange. The following procedure assumes
that the necessary pre-configuration in the Parameter Setting tool and the Signal
Matrix tool has been performed and tested to enable data exchange between IEDs
or between instances of voltage control in the same IED.
For parallel operation, it is also recommended to confirm the setting for the general
parallel arrangement of transformers in Main menu/Settings/Setting group N/
Control/TransformerVoltageControl(ATCC,90)/TR8ATCC:x/ParCtrl. General
parallel arrangement 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.

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/
General settings/Control/TransformerVoltageControl(ATCC,90)/
TR8ATCC: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/General settings/Control/
TransformerVoltageControl(ATCC,90)/TR8ATCC:x/ParCtrl/
CircCurrLimit.
Section 12
Primary injection testing
SEMOD176327-186 v3
SEMOD176327-195 v3
279