ABB PQFM Instruction Manual page 65

S1, k
S2, l
P1 P2
S1 S2
k
PQF 1
Figure 45: CT connections for the case of two independent transformers (to be done for each
For each phase, 3 CTs must be installed:
- one to measure I1
- one to measure I2
- one to measure I0.
The CTs must be identical: X/5 A.
CT I1 and CT I0 feed a summation CT which is connected to PQF1.
CT I2 and CT I0 feed a summation CT which is connected to PQF2.
The summation CTs must be rated 5+5 / 5 A.
Condition 1: the tie is open.
The filter PQF1 sees I1 and the filter PQF2 sees I2 (I0 = 0). The two transformers work
independently and the total current to be compensated is I1 + I2.
Condition 2: the tie is closed but both transformers feed the loads.
In this configuration, the filter PQF1 sees (I1-I0) and the filter PQF2 sees (I2+I0). The total
current seen by the two filters is I1 + I2.
Condition 3: the tie is closed but only one transformer feeds the loads (degraded mode).
If only T1 feeds the loads with the tie closed, PQF1 sees (I1-I0) and PQF2 sees I0 (I2 is
zero). If only T2 feeds the load, I1 will be zero.
Please note that the above described connection must be done for each phase. The CT
ratio to be programmed in the filter is: 2×X/5.
T1
P1, K
I1
I0
P1
K
P2, L
S1 S2
k
P1 P2
I'1-I'0
l
phase)
Manual Power Quality Filter PQFM ç Electrical design and installation 65
S1, k
P1, K
I2
S2, l
P2
L
P2, L
l
P1 P2
S1 S2
k
PQF 2
T2
P1 P2
I'2+I'0
l