ABB REL650 Applications Manual page 290

Section 10
Secondary system supervision
284
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Figure 127: Constant test current flow in parallel trip contacts and trip-circuit
supervision
Several trip-circuit monitoring functions parallel in circuit
Not only the trip circuit often have parallel trip contacts, it is also possible that the circuit
has multiple TCSSCBR circuits in parallel. Each TCSSCBR circuit causes its own
supervising current to flow through the monitored coil and the actual coil current is a sum
of all TCSSCBR currents. This must be taken into consideration when determining the
resistance of R .
ext
Setting the TCSSCBR function in a protection IED not-in-use does not
typically affect the supervising current injection.
Trip-circuit monitoring 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 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 TCSSCBR circuit
1MRK 506 334-UUS A
Application manual