The reach of phase overcurrent line protection is dependent of the operation state and thefault type. Therefore the setting must be based on fault calculations made for differentfaults, fault points and switching states in the network. Although it is possible to makehand calculations of the different faults it is recommended to use computer based faultcalculations. Different time delay principles can be used. This is due to different praxis.The following principle for the phase overcurrent protection is proposed:• Step 1 (I>>>) with high current setting and zero delay. This step gives fast trip for theline short circuits close to the nearest line end.• Step 2 (I>>) with a current setting that enables detection of all short circuits on theprotected line and on the local and remote busbars. The function has a short delay toenable selectivity.• Step 3 (I>) with a current setting that enables detection of all short circuits on theadjacent lines connected to the local and remote busbars. The function has a longerdelay to enable selectivity.2 1456A B7891080 %Y YREL 6503ANSI11000114_1_en.vsdREL 650ANSI11000114 V1 ENFigure 21: Fault points for phase overcurrent setting calculationsThe phase overcurrent protection in line end A is considered in this example. The sameprinciple can be used for line end B.3.1.9.1 Calculating general settings1. Set GlobalBaseSel to 1The settings are made in primary values. These values are given in the base settingsin Global base 1.2. Set DirModeSel1(2,3) to Non-directionalIt is assumed that the phase overcurrent protection shall operate also when thedistance protection is deactivated due to fuse failure. Therefore the function shall benon-directional as the directional function must use voltage measurement.1MRK 506 334-UUS A Section 3REL650 setting examples67Application manual
