Emax Low voltage air circuit-breakers - ABB Download Center

Directional protectionDirectional protection is based on the ability to correlate the circuit-breaker’s behavior with thedirection of the fault current.Two different trip times can be set on the PR123 trip unit depending on the current direction:– a time (t7Fw) for a direction of current concordant (Fw) with the reference direction set;– a time (t7Bw) for a direction of current discordant (Bw) with the reference direction set.A current threshold only (I7) can be set on the PR123 trip unit.If the fault current is discordant (Bw) with the reference direction, the protection shall intervenewhen the threshold I7 is reached within the set time t7Bw (provided that the functions S and Ihave not been set as to intervene before function D).If the fault current is concordant (Fw) with the reference direction, the protection shall intervenewhen the threshold I7 is reached within the set time t7Fw (provided that the functions S and Ihave not been set as to intervene before function D).Moreover, if function I is active and the short-circuit current exceeds the set value I 3, the circuitbreakerwill trip instantaneously independently of the direction of the current.The reference direction set by ABB is from the top of the circuit-breaker (the zone where the tripunit is located) towards the bottom.G1G2ReleaseReleaseReferencedirectionset byABBReferencedirectioninvertedthroughsoftwareReferencedirectionset byABB1SDC200189F00016The figure above shows the actual configuration the circuit-breakers have in the system. Thered arrow shows the reference direction set by default on the circuit-breaker.If the power supply direction of the circuit-breaker is from top to bottom (supply from G2), thereference direction must remain the one set by ABB.If the power supply direction of the circuit-breaker is from bottom to top (supply from G1), thenew PR123 trip unit allows the default setting to be inverted by operating on its software.ReferencedirectionACG1I>Contribution to theshort-circuit by each generator:10 kAQF1 withPR123DI>OtherpassiveloadsQF3 withPR222ReferencedirectionI>MEBG2I>QF4QF2 withPR123Contribution of themotor to theshort-circuit: 5 kA1SDC200190F0001In this way, all the quantities measured by the PR123 trip unit can be evaluated as they actuallyflow through the installation. Furthermore, in the wiring diagram of the system, the referencedirection to carry out a selectivitystudy and consider thetripping directions Bw or Fwcorrectly still remains from topto bottom.In the following wiring diagramthe reference directionsare shown in red. By consideringthe circuit-breakers suppliedas in the figure above, itcan be seen that for QF2 thisis the default direction,whereas for QF1 the directionhas been inverted by meansof the software.6/14ABB SACE