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Figure 8.3 shows two parallel lines, A and B, protected with
overcurrent relays R1, R2, R3 and R4. The relays R3 and R4 are
directional.
If there is a fault in one of the lines, only the faulty line will be
switched off because of the direction functions of the relays R3 and
R4. A detailed schematic of e.g. the relay R3 is shown in Figure 8.4.
Figure 8.4 – Example Connection of Allen-Bradley 857
Applications
Note: Both short-circuits and earth-faults
will be detected. The outgoing line is one of
several parallel lines or the line is feeding a
ring network.
857-UM001A-EN-P – July 2009
8-3
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