ABB RELION SMU615 Technical Manual page 139

1MRS758407 C
Figure 90: Improved connection for parallel trip contacts where the test current
flows through all wires and joints
Several trip circuit supervision functions parallel in circuit
Not only the trip circuit often have parallel trip contacts, it is also possible that
the circuit has multiple TCS circuits in parallel. Each TCS circuit causes its own
supervising current to flow through the monitored coil and the actual coil current is
a sum of all TCS currents. This must be taken into consideration when determining
the resistance of R
Trip circuit supervision with auxiliary relays
Many retrofit projects are carried out partially, that is, the old electromechanical
relays are replaced with new ones but the circuit breaker is not replaced. This
creates a problem that the coil current of an old type circuit breaker can be too
high for the merging unit trip contact to break.
The circuit breaker coil current is normally cut by an internal contact of the circuit
breaker. In case of a circuit breaker failure, there is a risk that the merging unit
trip contact is destroyed since the contact is obliged to disconnect high level of
electromagnetic energy accumulated in the trip coil.
SMU615
Technical Manual
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ext
Setting the TCS function in a merging unit not-in-use does not typically
affect the supervising current injection.
Supervision functions
139