ABB RELION REX640 Technical Manual page 670

Protection functions
When the test mode is active, the
differential protection function as in the normal operation mode. The setting can
be used for shifting the phase (0 or 180 degrees).
Figure 378: An example of a test mode situation where three-phase currents are
injected to the local end protection relay
4.3.1.7 Application
LNPLDF is designed for the differential protection of overhead line and cable
feeders in a distribution network. LNPLDF provides absolute selectivity and fast
operating times as unit protection also in short lines where distance protection
cannot be applied.
LNPLDF provides selective protection for radial, looped and meshed network
topologies and can be used in isolated neutral networks, resistance earthed
networks, compensated (impedance earthed) networks and solidly earthed
networks. In a typical network configuration where the line differential protection
scheme is applied, the protected zone, that is, the line or cable, is fed from two
directions.
Figure 379: Line protection with phase segregated line differential with in-zone
transformer
LNPLDF can be utilized for various types of network configurations or topologies.
Case A shows the protection of a ring-type distribution network. The network is
also used in the closed ring mode. LNPLDF is used as the main protection for
different sections of the feeder. In case B, the interconnection of two substations
is done with parallel lines and each line is protected with the line differential
protection. In case C, the connection line to mid scale power generation (typical size
670
CT connection type is still used by the line
RED 615
Communication
PROTECTED ZONE
1MRS759142 F
RED 615
REX640
Technical Manual