MC30-BC
Doc. N°
MO-0365-ING
Copyright 2008
FW 980.09.01.X
Date
15.06.2022
Rev.
1
Pag.
7
of
37
r
s
a
t
T
K
B
1
Is
I
A
t(I)
+
•
•
+
−
=
α
2.2.2.4 - Algorithm of the time current curves
The Time Current Curves are generally calculated with the following equation:
(1)
where:
t(I) =
Actual trip time delay when the input current equals “I”
I = Maximum of the three input currents.
Is = Set minimum pick-up level
K =
T
s
= Set time delay: t(I) = T
s
when
tr = Operation time of the output relay on pick-up (7ms).
The parameters “
A
” and “
a
” have different
values for the different Time Current Curves.
Curve Name
Curve Identifier
A
B
a
IEC A Inverse
A
0.14
0
0.02
IEC B Very Inverse
B
13.5
0
1
IEC C Extremely Inverse
C
80
0
2
IEEE Moderate Inverse
MI
0.0104
0.0226
0.02
IEEE Short Inverse
SI
0.00342
0.00262
0.02
IEEE Very Inverse
VI
3.88
0.0963
2
IEEE Inverse
I
5.95
0.18
2
IEEE Extremely Inverse
EI
5.67
0.0352
2
The maximum measuring current is “40xIn” for phase elements and “10xOn” for the neutral
element.
1
a
1
10
A
−
−
10
I
I
s
=
