ABB RELION REX640, Техническое руководство, Страница: 1314 / 1960

Open CT circuits create extremely high voltages in the circuits, which may
damage the insulation and cause further problems. This must be taken
into consideration especially when the protection functions are blocked.
When the reference current is not connected to the protection relay, the
function should be turned off. Otherwise, the
FAIL
output is activated
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
CCSPVC compares the sum of phase currents to the current measured with the
core-balanced CT.
Figure 747: Connection diagram for reference current measurement with core-
balanced current transformer
Current measurement with two independent three-phase sets of CT cores
Figure 748
and
Figure 749
show diagrams of connections where the reference
current is measured with two independent three-phase sets of CT cores.
Supervision functions 1MRS759142 F
1314 REX640
Technical Manual