Modeling the thermal part of the time current curve

[IbrahimAIbrahim]

G’ day,

I am working on designing protection devices for my research work and I am struggling to model the thermal part for the low voltage circuit breakers based on IEC standards.

Based on the standards, the time current curve for types B, C and D are as mentioned on the attached figure. I could not find the proper formula which represents the thermal characteristic for these types. Please, assist on this matter.

Thank you for your cooperation in advance.

 

[Careful_Bodger]

G'day cobber,
I think you'd be better off posting this on a maths Q&A site (maybe starting here .....https://math.stackexchange.com/search?q=curve+fit).
I assume you've tried a curve fit in Excel and searching some the original literature in fusing currents (e.g. https://ieeexplore.ieee.org/document/4499200)