3I0BC,step1 = 4 000 A and we getAI sel 1060298079040003 ,0 =×=GUID-F6D8356A-6802-4076-8240-0290B2C9C500 V1 EN (Equation 25)This calculation is made for fault out on each of the lines out from the remote busbar.To assure both sufficient reach of step 2 and selectivity the setting of step 2 must bechosen:1.2 · max(3I0,sel) ≤ INstep2 ≤ 0.7 · 3I0ABmin1.2 · 1 060 ≤ INstep2 ≤ 0.7 · 2 390 or 1 272 ≤ Nstep2 ≤ 1 673Setting: Pickup2= 140 % of IBase which corresponds to 1400 A2. Set t2 to 0.4 s3.1.10.4 Calculating settings for step 4The current setting of step 4 should be chosen according to standard procedure in the grid.From experience it can be concluded that the setting down to about 100 A can be used. Thissetting is however highly dependent on the line configuration, manly if the line istransposed or not.If definite time delay is used there is some risk of unselective trip at high resistive ground-faults or series faults. If dependent time delay (inverse time) is used some degree ofselectivity can be achieved.1. Set Pickup4 to 10 % of IBase which corresponds to 100 ACharacteristic 4: RD Type.2. Set TD4 to 0.33. Set: t4Min to 1.2 s3.1.11 Calculating settings for scheme communication for residualovercurrent protection ECPSCH (85)The communication logic is used to assure fast fault clearance for all ground-faults alongthe line, that is also for faults outside the reach of step 1 of the four step residualovercurrent protection. The logic for the communication schemes requires acommunication link between the four step residual overcurrent protections on the two lineends. The communication link alternatives are:Section 3 1MRK 506 334-UUS AREL650 setting examples74Application manual
