ABB RELION SMU615 Technical Manual page 137

1MRS758407 C
Figure 88: 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.
SMU615
Technical Manual
Supervision functions
137