APPENDIX
341
NVA100X-D - Manual - 02 - 2016
8.3
APPENDIX A3 - Inverse time ANSI/IEEE curves
Mathematical formula
The mathematical formula, according the ANSI/IEEE 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
= 0.01 for ANSI/IEEE Moderately inverse curve
K
= 3.922 for ANSI/IEEE Very inverse curve
K
= 5.64 for ANSI/IEEE Extremely inverse curve
α
= curve shape constant:
α
= 0.02 for ANSI/IEEE Moderately inverse curve
α
= 2 for ANSI/IEEE Very inverse curve
α
= 2 for ANSI/IEEE Extremely inverse curve
L
= coeffi cient:
L
= 0.023 for ANSI/IEEE Moderately inverse curve
L
= 0.098 for ANSI/IEEE Very inverse curve
L
= 0.024 for ANSI/IEEE Extremely inverse curve
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.
—
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
t
=
t
>
inv
·
[(
I
/
I
>
inv
)
α
-1]
K
+ L
t
=
t
>
inv
·
[(
I
/
I
>
inv
)
α
-1]
K
+ L
