ABB RET670 - Page 674

Avoidance of simultaneous tapping (operation with the master follower method)
A time delay for the follower in relation to the command given from the master can be
set when the setting MFMode is Follow Tap that is, when the follower follows the tap
position (with or without an offset) of the master. The setting parameter tAutoMSF then
introduces a time delay on VRAISE/VLOWER commands individually for each
follower, and effectively this can be used to avoid simultaneous tapping.
Homing
Homing (operation with the circulating current method)
This function can be used with parallel operation of power transformers using the
circulating current method. It makes possible to keep a transformer energized from the
HV side, but open on the LV side (hot stand-by), to follow the voltage regulation of
loaded parallel transformers, and thus be on a proper tap position when the LV circuit
breaker closes.
For this function, it is needed to have the LV VTs for each transformer on the cable
(tail) side (not the busbar side) of the CB, and to have the LV CB position hardwired to
the IED.
In TR8ATCC block for one transformer, the state "Homing" will be defined as the
situation when the transformer has information that it belongs to a parallel group (for
example, information on T1INCLD=1 or T2INCLD=1 ... and so on), at the same time
as the binary input DISC on TR8ATCC block is activated by open LV CB. If now the
setting parameter OperHoming = Enabled for that transformer, TR8ATCC will act in
the following way:
• The algorithm calculates the “true” busbar voltage, by averaging the voltage
measurements of the other transformers included in the parallel group (voltage
measurement of the “disconnected transformer” itself is not considered in the
calculation).
• The value of this true busbar voltage is used in the same way as V
set
for control of
a single transformer. The “disconnected transformer” will then automatically
initiate VRAISE or VLOWER commands (with appropriate t1 or t2 time delay) in
order to keep the LV side of the transformer within the deadband of the busbar
voltage.
Homing (operation with the master follower method)
If one (or more) follower has its LV circuit breaker open and its HV circuit breaker
closed, and if OperHoming = Enabled, this follower continues to follow the master just
as it would have made with the LV circuit breaker closed. On the other hand, if the LV
circuit breaker of the master opens, automatic control will be blocked and TR8ATCC
function output MFERR will be activated as the system will not have a master.
Adapt mode, manual control of a parallel group
Adapt mode (operation with the circulating current method)
Section 3 1MRK504116-UUS C
IED application
668
Application manual