Emax Low voltage air circuit-breakers - ABB Download Center

Primary and secondary distributionSelective protectionDual Setting6non-priority loadsThanks to the new PR123 tripunit, it is also possible to programtwo different sets of parametersand, through an externalcommand, to switchfrom one set to the other.This function is useful whenthere is an emergency source(generator) in the system, onlysupplying voltage in the caseof a power loss on the networkside.In the system described below,in the case of a loss of thenormal supply on the networkside, by means of the ABBSACE ATS010 automatictransfer switch, it is possibleto switch the supply from thenetwork to the emergencypower unit and to disconnectthe non-primary loads byopening the QS1 switchdisconnector.Under normal service conditionsof the installation, the circuit-breakersC are set in orderto be selective with bothcircuit-breaker A, on the supplyside, as well as with circuitbreakersD on the load side.By switching from the networkto the emergency power unit,circuit-breaker B becomes thereference circuit-breaker onthe supply side of circuitbreakersC. This circuitbreaker,being the protectionof a generator, must be set totrip times shorter than A andtherefore the setting values ofthe circuit-breakers on the loadside might not guarantee theselectivity with B.By means of the “dual setting”function of the PR123 trip unit,it is possible to switch circuitbreakersC from a parameterset which guarantees selectivitywith A, to another set whichmake them selective with B.However, these new settingscould make the combinationbetween circuit-breakers Cand the circuit-breakers on theload side non-selective.1SDC200316F00016/8ABB SACE