ABB REF615 Applications Manual page 196

Section 7
Supervision functions
190
A070970 V1 EN
Figure 94: Improved connection for parallel trip contacts
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 .
ext
Setting the TCS function in a protection IED not-in-use does not
typically effect the supervising current injection.
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 may be too high for the
protection IED 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 protection IED trip
contact is destroyed since the contact is obliged to disconnect high level of
electromagnetic energy accumulated in the trip coil.
An auxiliary relay can be used between the protection IED trip contact and the circuit
breaker coil. This way the breaking capacity question is solved, but the TCS circuit
1MRS756378 D
REF615
Application Manual