ABB REC670 Applications Manual page 404

Section 14
Control
398
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.
I cc....T2
T1
I cc....T1
I
T1
I
T1
U
B
I L
Load
U
L
IEC06000512 V1 EN-US
Figure 177: Capacitor bank on the LV-side
From figure 177 it is obvious that the two different connections of the capacitor
banks are 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
to the HV side will divide between the two transformers and it will be measured
with opposite direction for T2 and T1. This in turn would be misinterpreted as a
circulating current, and would upset a correct calculation of I
connection is as in the left figure the capacitive current I
for regardless of the operating conditions and in ATCC this is made numerically.
The reactive power of the capacitor bank is given as a setting Q1, which makes it
possible to calculate the reactive capacitance:
T2
I
T2
I
C
1MRK 511 401-UEN A
I cc....T2
T1
I cc....T1
I
T1
I I
T1 T2
U
B
I L
Load
U
L
en06000512.vsd
that goes
C
. Thus, if the actual
cc
needs to be compensated
C
Bay control REC670 2.2 IEC
Application manual
T2
I
T2
I
C