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Table 1 Overcurrent relay characteristics coefficient, according to IEC-60255 std

From: Coordination of dual setting overcurrent relays in microgrid with optimally determined relay characteristics for dual operating modes

Characteristic curve of relay α β Relay characteristics identifier (RCI)
Very inverse (VI) 13.5 1 1
Extremely inverse (EI) 80 2 2
Normal inverse (NI) 0.14 0.02 3