181
NC20 - Manual - 01 - 2015
APPENDIX
Phase overcurrent 50/51 RMS - Extremely inverse time curve (ANSI/IEEE type EI)
F_51-ANSIEI-Char.ai
1.1
2
3
4
5
6
7
8 9 10
20
I
RMS
/
I
>
inv
0.01
0.1
1
10
100
1000
10000
t
[s]
t
>
inv
=
10 s
t
>
inv
=
60 s
t
>
inv
=
5 s
t
>
inv
= 0.5 s
t
>
inv
= 1 s
t
>
inv
= 0.2 s
t
>
inv
= 0.1 s
t
>
inv
= 0.02 s
t
=
t
>
inv
·
[(
I
RMS
/
I
>
inv
)
2
-1]
5.64
+ 0.024
Note: match of operating and setting time takes place when
I
RMS
/
I
>
inv
= 2.789
