ABB Relion 670 Series Applications Manual page 412

Section 15
Control
The follower in manual mode will of course disregard any possible tapping of the master.
However, as one transformer in the parallel group is now exempted from the parallel control,
the binary output signal ADAPT on TR8ATCC function block will be activated for the rest of the
parallel group.
Plant with capacitive shunt compensation (for operation with the circulating current
method)
If significant capacitive shunt generation is connected in a substation and it is not
symmetrically connected to all transformers in a parallel group, the situation may require
compensation of the capacitive current to the ATCC.
An asymmetric connection will exist if for example, the capacitor is situated on the LV-side of a
transformer, between the CT measuring point and the power transformer or at a tertiary
winding of the power transformer, see figure 211. In a situation like this, the capacitive current
will interact in opposite way in the different ATCCs with regard to the calculation of circulating
currents. The capacitive current is part of the imaginary load current and therefore essential in
the calculation. The calculated circulating current and the real circulating currents will in this
case not be the same, and they will not reach a minimum at the same time. This might result in
a situation when minimizing of the calculated circulating current will not regulate the tap
changers to the same tap positions even if the power transformers are equal.
However if the capacitive current is also considered in the calculation of the circulating
current, then the influence can be compensated for.
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IEC06000512 V2 EN-US
Figure 211: Capacitor bank on the LV-side
From figure
completely the same regarding the currents in the primary network. However the CT measured
currents for the transformers would be different. The capacitor bank current may flow entirely
to the load on the LV side, or it may be divided between the LV and the HV side. In the latter
case, the part of I
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211 it is obvious that the two different connections of the capacitor banks are
that goes to the HV side will divide between the two transformers and it
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IEC06000512-2-en.vsd
1MRK 511 401-UEN Rev. K
SEMOD159053-238 v4
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Bay control REC670
Application manual