ABB Relion SMU615 Technical Manual page 132

Section 5
Supervision functions
126
A051906 V4 EN
Figure 86: Operating principle of the trip-circuit supervision without an external
resistor. The circuit breaker open indication is set to block TCSSCBR
when the circuit breaker is open.
Trip circuit supervision and other trip contacts
It is typical that the trip circuit contains more than one trip contact in parallel, for
example in transformer feeders where the trip of a Buchholz relay is connected in
parallel with the feeder terminal and other relays involved. The supervising current
cannot detect if one or all the other contacts connected in parallel are not connected
properly.
1MRS758407 B
SMU615
Technical Manual