ABB REG670 Applications Manual page 572

Section 15
Control
566
I
cc....T2
T1
I
cc....T1
I
T1
I
T1
U
B
I L
Load
U
L
IEC06000512 V1 EN
Figure 289: Capacitor bank on the LV-side
From figure 289 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
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
capacitive current I needs to be compensated for regardless of the operating
C
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:
2
U
=
X
C
Q 1
EQUATION1871 V1 EN
Thereafter the current I
C
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
T2
I
T2
I
C
. Thus, if the actual connection is as in the left figure the
cc
at the actual measured voltage U
1MRK 502 071-UEN -
I
cc....T2
T1
I
cc....T1
I
T1
I I
T1 T2
U
B
I L
Load
U
L
en06000512.vsd
that goes to the HV side will divide
C
can be calculated as:
B
Application manual
T2
I
T2
I
C
(Equation 274)