Homing (operation with the circulating current method)
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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 L
V 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 = On 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 U
set
for
control of a single transformer. The “disconnected transformer” will then
automatically initiate URAISE or ULOWER 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)
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If one (or more) follower has its LV circuit breaker open and its HV circuit breaker
closed, and if OperHoming = On, 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
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Adapt mode (operation with the circulating current method)
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When the circulating current method is used, it is also possible to manually control
the transformers as a group. To achieve this, the setting OperationAdapt must be
set On, then the control mode for one TR8ATCC shall be set to “Manual” via the
binary input MANCTRL or the local HMI under Main menu/Control/
Commands/TransformerVoltageControl(ATCC,90)/TR8ATCC:x whereas the
other TR8ATCCs are left in “Automatic”. TR8ATCCs in automatic mode will then
observe that one transformer in the parallel group is in manual mode and will then
automatically be set in adapt mode. As the name indicates they will adapt to the
manual tapping of the transformer that has been put in manual mode.
Section 12 1MRK 506 375-UEN A
Control
304 Railway application RER670 2.2 IEC
Application manual
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