Step 1: Calculate the fault current (I) by multiplying it by the setting current (I set)., IEC Normal, IEC Very Inverse, etc. Step 3: Enter K, P, & TMS values into the formula. There are three main types of overcurrent relay: (1) Instantaneous, (2) Time-Dependent (Definite time or inverse), and (3) Mixed (Definite time and Inverse). Instantaneous relays have operating times usually less than 3 cycles. What is a Time Overcurrent Relay? Inverse Definite Minimum Time (IDMT) relays activate when current exceeds a predetermined pickup value with the. Relay coordination is the process of selecting settings that will assure that the relays will operate in a reliable and selective way. Was this calculator helpful? Input the rated primary current of the Current Transformer (CT), typically. 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. These tools assist in determining the trip time of relays if a fault current exceeds.
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