Threestage overcurrent protection (Ⅰ, Ⅱ, Ⅲ) ensures selective, fast, and reliable fault clearance in power systems. This guide explains its necessity, coordination logic, and stepbystep setting methods for each stage. 1 shows a time-graded protection arrangement in a radial network. For the low-set stage (3I>), either inverse time or definite time cha-racteristic can be given. They are intended to quickly identify a fault and isolate it so the balance of the system. with a pickup setting of 480 amperes and 1-1/2 time-dial setting.