ABB ret650, Руководство по применению, Страница: 211 / 392

The calculated circulating current I
cc_i
for transformer “i” is shown on the HMI as
a service value ICIRCUL under Main menu/Test/Function status/Control/
TransformerVoltageControl(ATCC,90) .
When the circulating current is known, it is possible to calculate a no-load voltage
for each transformer in the parallel group. To do that the magnitude of the
circulating current in each bay, is first converted to a voltage deviation, U
di
, with
equation 50 :
_ di i cc i i
U C I X
= ´ ´
EQUATION1869 V1 EN-US
(Equation 50)
where X
i
is the short-circuit reactance for transformer i and C
i
, is a setting
parameter named Comp which serves the purpose of alternatively increasing or
decreasing the impact of the circulating current in TR8ATCC control calculations.
It should be noted that U
di
will have positive values for transformers that produce
circulating currents and negative values for transformers that receive circulating
currents.
Now the magnitude of the no-load voltage for each transformer can be
approximated with:
i Bmean di
U U U
= +
EQUATION1870 V1 EN-US
(Equation 51)
This value for the no-load voltage is then simply put into the voltage control
function for single transformer. There it is treated as the measured busbar voltage,
and further control actions are taken as described previously in section
"Automatic
voltage control for a single transformer" . By doing this, the overall control strategy
can be summarized as follows.
For the transformer producing/receiving the circulating current, the calculated no-
load voltage will be greater/smaller than the measured voltage U
Bmean
. The
calculated no-load voltage will then be compared with the set voltage USet . A
steady deviation which is outside the outer deadband will result in ULOWER or
URAISE being initiated alternatively. In this way the overall control action will
always be correct since the position of a tap changer is directly proportional to the
transformer no-load voltage. The sequence resets when U
Bmean
is inside the inner
deadband at the same time as the calculated no-load voltages for all transformers in
the parallel group are inside the outer deadband.
In parallel operation with the circulating current method, different USet values for
individual transformers can cause the voltage regulation to be unstable. For this
reason, the mean value of
USet for parallel operating transformers can be
automatically calculated and used for the voltage regulation. This is set On / Off by
setting parameter OperUsetPar . The calculated mean USet value is shown on the
local HMI as a service value USETPAR under Main menu/Test/Function status/
Control/TransformerVoltageControl(ATCC,90) .
1MRK 504 169-UEN A
Section 11
Control
Transformer protection RET650 2.2 IEC 205
Application manual