IDMT Curve formula of IEC

IEC 60255 Curves Equation:

Where,

       TMS   denoted time multiplier setting

       Is          denoted the current setting.

       I           denoted the actual current.

       k and α  denoted the curve type constants. See table below.

Curve type	k	α
Standard inverse	0.140	0.020
Very inverse	13.5	1
Extremely inverse	80	2
Long time standard inverse	120	1