Use this Protection Relay Setting Calculator to calculate pickup current, time multiplier settings (TMS), operating time, coordination time interval (CTI), and plug setting multiplier (PSM) using fault current, CT ratio, and IEC 60255 curve parameters. Relay coordination is the process of selecting settings that will assure that the relays will operate in a reliable and selective way. For overcurrent. Selective short-circuit protection can be achieved in different ways, such as: Time-graded protection Time- and current-graded protection A straightforward way of obtaining selective protection is to use time grading. They can then directly compare th e relay voltage. Professional protection relay testing calculator implementing IEEE C37.