Application Guide - NP900 Series
115 (504
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A996A
In case when the current based protection activates so that either Iset and/or I0Sset
current threshold setting are exceeded the counter for CBFP is halted until the monitored
output contact is controlled (primary protection operates). From the tripping signal of the
primary protection stage the counter for CBFP start to calculate the set operating time.
The tripping of the primary protection stage is constantly monitored in this configuration
and if the current is not decreased under the setting limit and the trip signal from primary
stage is not reset CBFP will be issued to upstream breaker. If the primary protection
function clears the fault e.g. the circuit breaker operates normally the counter for CBFP is
reset immediately the current is measured below the threshold settings or the trip signal is
reset. This configuration allows the CBFP to be controlled on current based functions only
and other function trips can be excluded from the CBFP functionality.
Figure 3.2.9.4-56 CBFP when selected criteria is current or DO.
The counter for CBFP starts to calculate the set operating time either from current
exceeding the setting limit or from the primary protection stage trip signal. The tripping of
the primary protection stage is constantly monitored in this configuration regardless of the
current status. The pick-up of CBFP is active until current is not decreased under the
setting limit or the trip signal from primary stage is not reset. In case if either of these
conditions are met until the timers set time first is issued retrip and if either of the
conditions is active also CBFP will be issued to upstream breaker. If the primary
protection function clears the fault e.g. the circuit breaker operates normally the counter
for CBFP is reset immediately the current is measured below the threshold settings and
the trip signal is reset. This configuration allows the CBFP to be controlled on current
based functions with added security from the current monitoring of the CBFP function and
other function trips can be also included to the CBFP functionality.
