The fault current fed to the protection shall be calculated for the fault points 3, 4, 5and 6 (faults about 80 % out on the adjacent lines connected to the local and remotebusbar).The fault at point 3 is calculated with minimum source impedance at substation Aand with one line out from substation B taken out of service. This results in thecurrent Ifault3,max.= 1.56 kA.The fault at point 4 is calculated with minimum source impedance at substation Aand with one line out from substation B taken out of service. This gives the currentIfault4,max.= 1.4 kA.The fault at point 5 is calculated with minimum source impedance at substation Band with one line out from substation A taken out of service. This gives the currentIfault5,max.= 1.56 kAThe fault at point 6 is calculated with minimum source impedance at substation Band with one line out from substation A taken out of service. This gives the currentIfault6,max.= 1.35 kA.The current setting of step 2 is, if possible, chosen as:1.2 · max(Ifault3,4,5,6max) ≤ Istep2 ≤ 0.7 · min(IAB,min, IBA,min)1.2 · 1.56 ≤ Istep2 ≤ 0.7 · 2.50 or 1.9 ≤ Istep2 ≤ 1.75In this case, it is not possible to fulfil the requirement above. Priority is given toselectivity, choosing setting 1900 A and accepting a small risk that short circuitsclose to the remote busbar are not tripped. This is acceptable as the distanceprotection normally gives sufficient coverage of the whole line and remote busbarfrom zone 2.Setting: Pickup2= 190 % of IBase which corresponds to 1 900 A.2. Set t2 to 0.4 sIf possible the delay of step 2 should be set equal to the distance protection zone 2(normally 0.4 s). To assure selectivity with this time delay the function should notoverreach adjacent lines out from the remote busbar and out from the local busbar.3.1.9.4 Calculating settings for step 31. Set Pickup3 to 110 % of IBaseTo assure that step 3 detects all short circuits on the adjacent lines out from theremote busbar a phase-phase short circuit is applied at fault points 7 and 8. The1MRK 506 334-UUS A Section 3REL650 setting examples69Application manual
