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APPENDIX
357
NVA100X-D - Manual - 02 - 2016
8.4
APPENDIX A3 - Inverse time - RECTIFIER, I2t and EM curves
Mathematical formula
The mathematical formula for RECTIFIER, I-squared-t (I
2
t) and Electromechanical curves (EM) 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
= 2351 for RECTIFIER curve (RI)
K
= 16 for I
2
t curve
K
= 0.28 for Electromechanical curve (EM)
α
= curve shape constant:
α
= 5.6 for RECTIFIER curve (RI)
α
= 2 for I-squared-t (I
2
t) curve
α
= -1 for Electromechanical curve (EM)
A
= coeffi cient:
A
= 1 for RECTIFIER curve (RI)
A
= 1 for I-squared-t (I
2
t) curve
A
= -0.236 for Electromechanical curve (EM)
B
= coeffi cient:
B
= 1 for RECTIFIER curve (RI)
B
= 0 for I-squared-t (I
2
t) curve
B
= -0.339 for Electromechanical curve (EM)
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
·
A·(
I
/
I
>
inv
)
α
-B]
K
t
=
t
>
inv
·
A·(
I
/
I
>
inv
)
α
-B]
K