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184
NC20 - Manual - 01 - 2015
APPENDIX
Residual overcurrent 50N/51N - Extremely inverse time curve (ANSI/IEEE type EI)
F_51N-ANSIEI-Char.ai
1.1
2
3
4
5
6
7
8 9 10
20
I
EC
/
I
E
>inv
0.01
0.1
1
10
100
1000
10000
t
[s]
t
E
>
inv
=
10 s
t
E
>
inv
=
60 s
t
E
>
inv
=
5 s
t
E
>
inv
= 0.5 s
t
E
>
inv
= 1 s
t
E
>
inv
= 0.2 s
t
E
>
inv
= 0.1 s
t
E
>
inv
= 0.02 s
t
=
t
E
>
inv
·
[(
I
EC
/
I
E
>
inv
)
2
-1]
5.64
+ 0.024
Note: match of operating and setting time takes place when I
EC
/I
E
>
inv
= 2.789
