ABB 615 series Technical Manual page 497

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615 series ANSI
Technical Manual
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Figure 241: Line differential applications
Communication supervision
A typical line differential protection application includes 87L as the main protection.
Backup over current functions is needed if a protection communication failure occurs.
When the communication supervision function detects a failure in the communication
between the protective units, the safe operation of the line is still guaranteed by blocking
the line differential protection and unblocking the over current functions.
When a communication failure is detected, the protection communication supervision
function issues block for the 87L line differential protection and unblock for the
instantaneous and high stages (instance 2) of the over current protection. These are used
to give backup protection for the remote end feeder protection relay. In situations where
the selectivity is weaker than usually, the protection should still be available for the
system.
Section 4
Protection functions
491