Broken Conductor Example; Circuit-Breaker Maintenance - Siemens 7SR10 Argus Series Manual

7SR10, 7SR11, 7SR12 Applications Guide

5.6.1 Broken Conductor example

Information recorded during commissioning:
I full load = 500A
I NPS = 50A
Therefore the ratio is given by 50/500 = 0.1
To allow for tolerances and load variation a setting of 200% of this value is recommended and
therefore the ratio for 46BC setting should be set at 20%.
To allow for adequate time for short circuit fault clearance by time delayed protection the 46BC delay
should be set to 50seconds.
To ensure the broken conductor protection does not operate incorrectly during low load conditions,
where the three phases are less than 10% of normal load, the element should be inhibited by setting
the 46BC U/C Guarded to Yes and selecting a 46BC U/C Guard Setting to 0.1 x In
5.7

Circuit-Breaker Maintenance

2
The Relay provides Total, Delta and Frequent CB Operation Counters along with an I t Counter to estimate the
amount of wear and tear experienced by a Circuit-Breaker. Alarm can be provided once set levels have been
exceeded.
Typically estimates obtained from previous circuit-breaker maintenance schedules or manufacturers data sheets
are used for setting these alarm levels. The relay instrumentation provides the current values of these counters.
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