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

1MRK 504 165-UUS -
12.1.2
12.1.3
Transformer protection RET670 2.2 ANSI
Commissioning manual
physical wiring or the current direction convention selected for the CT analogue input as
part of the setting in the PST setting.

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 Enabled except the parameter corresponding to the IED itself. For
example, do not set T1RXOP to Enabled in IED T1 or T2RXOP to Enabled in IED T2.
For example, if IEDs T1, T2 and T3 are connected,
• In instance 1 of TR8ATCC (90), set T2RXOP and T3RXOP to Enabled.
• In instance 2 of TR8ATCC (90), set T1RXOP and T3RXOP to Enabled.
• In instance 3 of TR8ATCC (90), set T1RXOP and T2RXOP to Enabled.

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
(VB) 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 VB values is calculated.
The resulting value VBmean is then used in each IED instead of VB 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/
Section 12
Primary injection testing
289