• The currents from the secondary side of the power transformer are used for
calculating the circulating current in the Negative Reactance Principle (NRP) and
Minimizing Circulating Current (MCC) operation modes.
Both voltage U_AB and the phase currents from the secondary side (I_x, where
x is A, B or C) are always measured using the value of the filtered fundamental
frequency component (DFT). Hence, the harmonics are always suppressed.
Moreover, the measured voltage value is continuously average-filtered with
the eight-value-long sliding window where the resulting filtering delay is not
compensated. The phase-compensated voltage U_A is always used in calculations,
although it is not connected. U
m
is the averaged value used for control and its
magnitude can be read from the monitored data U_MEAS.
Similarly, the magnitude of the phase current of the own transformer, I_x, and
the phase angle difference between the internally phase-compensated voltage
U_A and phase current I_x are also average-filtered by the same length-fixed
window. The phase angle value can be read from the monitored data ANGL_UA_IA.
These currents and phase angle differences are used solely on circulating current
calculations.
The angle difference is used in
There are minimum limits for the voltage and current magnitudes, resulting in
the magnitude and phase angle difference values diverging from zero. The voltage
magnitude must exceed three percent of U
n
and the current I_A must exceed two
percent of I
n
.
9.5.4.2
Tap changer position inputs
The position value of the tap changer can be brought to OLATCC as a resistance
value, a mA signal or as a binary-coded signal. More information on how the
resistance value, the mA signal or a binary-coded interface are implemented can
be found in TPOSYLTC in the technical manual of the IED.
The indicated tap changer position of the own transformer is internally connected
to the
TAP_POS
input, and the tap changer positions of the parallel transformers
are fed to the other
TRx_TAP_POS
inputs. This also defines the connection identity
so that follower 1 is connected to
TR1_TAP_POS
, follower 2 is connected to
TR2_TAP_POS
and follower 3 is connected to
TR3_TAP_POS
. The own transformer
position can be read from the monitored data
TAP_POS
. The follower tap changer
positions can also be read from the input data
TRx_TAP_POS
, where x is a value
between 1 and 3.
The tap changer position value is given in parentheses. For example, (0) indicates
that there is no tap changer position connected or the tap changer position value
quality is bad. Typically, if no tap changer position is connected, all the TPOSYLTC
binary inputs are FALSE by default and the value shown is (0). A value other than
zero indicates bad quality. A bad-quality tap changer position is dealt by OLATCC
like unconnected tap position information.
9.5.4.3
Operation mode selection
OLATCC has the
Operation mode and Auto parallel mode settings for selecting the
desired operation mode. The
Operation mode setting can have any of the following
values: "Manual", "Auto single", "Auto parallel", "Input control" and “Command”. If
Control functions
1MRS757644 H
1048
620 series
Technical Manual
