ABB RELION REX640 Technical Manual page 589

1MRS759142 C
REX640
Technical Manual
small distribution transformer is located at the tapped load. The usage of LNPLDF is
not limited to these applications.
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Figure 321: Line differential applications
Communication supervision
A typical line differential protection application includes LNPLDF 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 LNPLDF 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
583