ABB Relion 620 Series, Technical Manual, Page: 1059 / 1224

The circulation current can be read from the monitored data I_CIR.
Using the circulating current, the compensation term U
ci
can be calculated with the
equation
U
I
I
U
ci
ci
CT n
n
=
−
⋅ ⋅
_ 1
100
Stability
(Equation 190)
I
ci
Circulating current, primary value
I
CT_n1
Nominal primary current of the CT
Stability
factor
Stability setting (the recommended value depends on the loop impedance)
Using the circulating current, a compensation term U
ci
can be calculated using
Equation 188
. The value of U
ci
, which can be positive or negative, is considered by
adding it to the
Band center voltage U
s
(
Equation 184
). According to
Figure 562
and
Equation 189
, the phasor information from the other IEDs is needed.
Parallel unit detection and the MCC mode
The network connection status information is essential for the MCC operation
mode. The status FALSE needs to be connected to the
CON_STATUS
input to ensure
a proper operation of the MCC calculation if the transformer is disconnected but
OLATCC remains in the MCC mode. This way the disconnected transformer is
excluded from the circulating current calculations.
The
CON_STATUS
input is used to identify if a certain transformer controller is able
to send the current information to other transformer controllers for circulating
current minimization purposes. As a result, this input has effect only in the MCC
or Manual acting operation modes. In these modes, if
CON_STATUS
is TRUE, the
information transmission is started. The circulating current information receiving
is allowed only in the MCC acting operation mode when
CON_STATUS
is TRUE.
PAR_UNIT_MCC can be seen in the monitored data view.
Communication and the MCC mode
The phasor information from the other parallel IEDs is needed for the circular
current calculation. Therefore, horizontal GOOSE communication is needed
between IEDs when the MCC principle is used.
The transferred current phasor contains the primary value of the measured
current. The received current phasor information can be read from the input data
TRx_I_AMPL
and
TRx_I_ANGL
for the magnitude and angle respectively. The value
"x" gives the connected parallel transformer number, a value between 1 and 3.
The sent phasor information always represents the difference between the voltage
phasor
U_A and I_A. This information regarding the current phasor can be read
from the output data
TR0_I_AMPL
and
TR0_I_ANGL
. The allowed acting operation
modes for sending data are MCC or Manual, both with the input
CON_STATUS
activated. The communication can be seen to be active when the sent and received
phasor magnitude is not clamped to zero. The communication phasor magnitude
found to be zero results either from a rejected acting operation mode or too low
signal magnitudes (see
Chapter 9.5.4.1 Voltage and current measurements
). Active
CON_STATUS
indicates that the corresponding transformer is connected to network
1MRS757644 H Control functions
620 series
Technical Manual
1059