ABB RELION 620 Series Technical Manual page 598

Section 6
Supervision functions
592
when unbalance occurs in the phase currents even if there was nothing
wrong with the measurement circuit.
Reference current measured with core-balanced current transformer
CCM compares the sum of phase currents to the current measured with the core-balanced
CT.
IL1
IL2
IL3
GUID-DA7A48EF-0F07-4665-9A09-87188E5A9982 V1 EN
Figure 301: Connection diagram for reference current measurement with core-
balanced current transformer
Current measurement with two independent three-phase sets of CT cores
Figure 302 and Figure 303
measured with two independent three-phase sets of CT cores.
I_A
I_B
I_C
I_REF
show diagrams of connections where the reference current is
1MAC504801-IB E
IED
CCM
FAIL
I_A
I_B
ALARM
I_C
I_REF
BLOCK
620 series ANSI
Technical Manual