Thytronic SIF5600 - 8 APPENDIX; 8.1 Appendix A1 - Inverse Time IEC Curves; Mathematical Formula

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SIF5600 - Manual - 03 - 2008
8 A P P E N D I X
8.1 APPENDIX A1 - Inverse time IEC curves
Mathematical formula
The mathematical formula, according the IEC 60255-3/BS142 standards is:
[1]
Where:
t = operate time (in seconds)
t
I>inv
= setting time multiplier (in seconds)
I = input current
I>
inv
= threshold setting
Coefficient
[2]
K = 0.14 for IEC-A curve (Normal inverse)
K = 13.5 for I
EC-B curve (Very inverse)
K = 80 for I
EC-C curve (Extremely inverse)
Curve shape constant
α = 0.02 for IEC-A curve (Normal inverse)
α = 1 for I
EC-B curve (Very inverse)
α = 2 for I
EC-C curve (Extremely inverse)
For all inverse time characteristics, following data applies:
Asymptotic reference value (minimum pickup value): 1.1 I>
inv
Minimum operate time: 0.05 s
Range where the equation is valid: 1.1 ≤ I
/I>
inv
≤ 20
Note 1 Symbols are concerning the overcurrent element.
Note 2 For SIF5600 devices with previous 2.00 fw release (normalization at fourfold threshold), the K coefficient is:
K = 0.028 for IEC-A curve (Normal inverse)
K = 3 for IEC-B curve (Very inverse)
K = 15 for IEC-C curve (Extremely inverse)
The “SIF5600-Manual-10-2006” reference document must be used
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t =
t>
inv
·
[(I/I>
inv
)
α
-1]
K