Thytronic NC20 User Manual

165
NC2 0 - Manual - 01 - 2015
APPENDIX
8 A P P E N D I X
8 APPENDIX
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
K = coeffi cient:
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>
inv
Minimum operate time: 0.1 s
Range where the equation is valid:
[2][3]
1.1 ≤ I /I>
inv
≤ 20
If I> pickup ≥ 2.5 I
n
, the upper limit is 50 I
n
Note 1 Symbols are concerning the overcurrent element. The comprehensive overview of the inverse time characteristics concerning the 50/51 and
50N/51N elements is dealt within the PROTECTIVE ELEMENTS section
Note 2 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
Nota 3 With setting more than 2.5 In for the 50/51 elements and 0.5 IEn for the 50N/51N elements, the upper limit of the measuring range is limited to 50
In and 10 IEn respectively.
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t =
t>
inv
·
[(I/I>
inv
)
α
-1]
K
t =
t>
inv
·
[(I/I>
inv
)
α
-1]
K

Thytronic NC20 Specifications

General

Brand	Thytronic
Model	NC20
Category	Power distribution unit
Language	English