Emax Low voltage air circuit-breakers - ABB Download Center

Directional protectionDirection (OUT-IN)Bw ➞ BwBw ➞ FwFw ➞ FwReference DirectionArrow4) in the case of a fault in D, circuit-breaker QF3 is passed through by a current from busbar B1;this current flows in the same direction as the one set. The OUT Fw bus of QF3 “blocks” the INFw bus of circuit-breakersQF1 +PR123AG1I>INFw BwOUTFw BwQF2 +PR123BG2I>INFw BwOUTFw BwQF1 and QF2: in fact, bothcircuit-breakers are passedthrough by fault currents concordantwith the direction set(the active “block” signals areindicated by wider arrows).CB1QF3 +PR123I>INFw BwOUTFw BwDM1SDC200194F0001The following example analyses a network with a bus-tie and takes the behavior of the protectiondevices in the presence of faults into consideration:6Direction (OUT-IN)Fw ➞ FwFw ➞ BwBw ➞ FwReference DirectionArrow-B1INFw BwOUTFw BwAI>-TM1IkQF1 +PR123INFw BwOUTFw BwI>QF2 +PR123I>-TM2INFw BwOUTFw Bw-B21) Fault in B1 with the bus-tie closed: only circuit-breakers QF1 and QF3 must interrupt the fault: inparticular, circuit-breaker QF3 is passed through by a current from busbar B2 (therefore in thesame direction as the one set); the OUT Fw bus sends a “block” signal to the IN Fw bus of circuitbreakerQF2 (passed throughby a current flowing from transformerTM2 and consequentlyin a direction concordant withthe one set), and to the IN Bwbus of circuit-breaker QF5(passed through from a currentflowing from the motor andconsequently in a direction discordantwith the one set).INFw BwOUTFw BwI>QF4 +PR123QF3 +PR123QF5 +PR123I>INFw BwOUTFw BwLM1SDC200320F00016/18ABB SACE