ABB RELION 620 Series Technical Manual page 589

1MAC504801-IB E
620 series ANSI
Technical Manual
A070970-ANSI V1 EN
Figure 294: 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 TCM circuits in parallel. Each TCM circuit causes its own supervising
current to flow through the monitored coil and the actual coil current is a sum of all TCM
currents. This must be taken into consideration when determining the resistance of R
Setting the TCM function in a protection relay not-in-use does not
typically affect 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 can be too high for the protection relay 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 relay trip contact is
Section 6
Supervision functions
.
ext
583