Self-Supervision - ABB REX 521 Technical Reference Manual, General

REX 521
4.1.11.
20
Protection Relay
Technical Reference Manual, General
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If there are more auxiliary contacts available, an opening contact can be series
connected with the R -resistor. The shunt-resistor circuit is opened when the CB is
ext
closed. Therefore the supervision of the auxiliary contact is also possible.

Self-supervision

In order to avoid false operations due to relay faults and to maximize the overall
availability of the protection, a set of autodiagnostic circuit arrangements have been
implemented in the relay modules.
The different memory circuits, i.e. the RAM and the non-volatile memories, are
continuously tested with different methods.
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1MRS 751108-MUM