Siemens 7SR23 DAD, Manual

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Chapter 7) 7SR23 DAD Applications Guide
©2013 Siemens Protection Devices Limited Chapter 7 Page 31 of 42
6.2 Busbar Protection
Figure 6-2 Single Busbar Protection
6.2.1 Primary Operate Current (Fault Setting)
To achieve correct sensitivity to in-zone faults, the protection scheme must typically operate for a primary current
of 10-30% of the minimum primary fault current,
For solidly earthed systems, where the fault current will be very high, it is acceptable practice to use a primary
fault setting of 50% of the Busbar full load current.
6.2.2 CT Supervision Settings
Generally a current setting of 2 - 10% of the full load rating of the busbar is acceptable.
Typically a setting of 2 to 10 seconds is applied.
6.2.3 Stability Level
The assigned through fault current shall be taken as the switchgear breaking capacity.
6.2.4 Double Busbar Protection
On double busbar systems, where there will be a significant number of switching operations, it is usual to provide
an extra level of tripping security by fitting a Check Zone relay. This monitors the current of every incomer and
outgoing feeder on the Busbar, but not the internal Busbar Sections and Couplers.
A Check Zone relay is also sometimes installed on single busbar systems of high importance.
The outputs of the relays protecting each Busbar zone are then connected in series with the Check Zone relay’s
outputs. Only when both operate will a trip be issued.