ABB Relion 670 Series Applications Manual page 240

Section 10
Unbalance protection
Differential CT
IEC19000197 V1 EN-US
Figure 110: Grounded/ungrounded single WYE connected SCB with CT arrangement
For a grounded/ungrounded H-bridge connection, each phase is divided into two main strings
and the midpoints of the strings are tied together. The unbalance current flowing through the
common point can be measured by using a normal CT.
L1
L2
L3
Strings
IEC19000198 V1 EN-US
Figure 111: Grounded/ungrounded H-bridge connected SCB with CT arrangement
234
L1
I
L1
L2
L3
C
C
C
Strings
C
I
UNB1
I
L1
Normal CT
C
C
I
UNB1
C
C
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I
L2
C
C C
C
C C
C
C C
C
C C
I
UNB2
Grounded/Ungrounded
I
L2
C
C
I
UNB2
C
C
N
Grounded/Ungrounded
1MRK 511 401-UEN Rev. K
I
L3
C C
C C
C C
C C
C C
C C
C C
C C
I I
UNB3 UNB3
IEC19000197-1-en-us.vsdx
I
L3
C
C
I
UNB3
C
C
IEC19000198-1-en-us.vsdx
Bay control REC670
Application manual