• The highest phase current value is used for overcurrent blocking.
• The currents from the secondary side of the power transformer are used for
line drop compensation (average of the connected inputs).
• 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 Equation 91, Equation 92 and
Equation 94.
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
.
9.5.6 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 TPOSSLTC 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.
1YHT530004D05 D Section 9
Control functions
615 series 729
Technical Manual
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