Thytronic NG10 - Appendix; APPENDIX A1 - Inverse Time IEC Curves; Mathematical Formula

APPENDIX
119
NG10 - Manual - 04 - 2022
8 APPENDIX8 APPENDIX
8.1 APPENDIX A1 - Inverse time IEC curves
 Mathematical formula
The mathematical formula, according the IEC 60255-3/BS142 standards is:
Where:
• t = operate time (in seconds)
• t
E>inv
= setting time multiplier (in seconds)
• I
E
= residual current input
• I
E
>
inv
= threshold setting
K = coefficient:
• K = 0.14 for IEC-A curve (Normal inverse)
• K = 13.5 for IEC-B curve (Very inverse)
• K = 80 for IEC-C curve (Extremely inverse)
α = curve shape constant:
• α = 0.02 for IEC-A curve (Normal inverse)
• α = 1 for IEC-B curve (Very inverse)
• α = 2 for IEC-C curve (Extremely inverse)
For all inverse time characteristics, following data applies:
• Asymptotic reference value (minimum pickup value): 1.1 I
E
>
inv
• Minimum operate time: 0.1 s
• Range where the equation is valid:
[1]
1.1 ≤ I
E
/I
E
>
inv
≤ 20
• If I
E
> pickup ≥ 0.6 I
En
, the upper limit is 12 I
En
Note 1 When the input value is more than 20 times the set point , the operate time is limited to the value corresponding to 20 times the set point
t =
t
E
>
inv
·
[(I
E
/I
E
>
inv
)
α
-1]
K