IM30-SA
Doc. N° MO-0089-ING
Rev.
1
FW:
1.01
Pag.
5
of
25
Copyright 2010 - Microener
r
s
a
t
T
K
B
1
Is
I
A
t(I)
2.2 - ALGORITHM OF THE TIME CURRENT CURVES
The Time Current Curves are generally calculated with the following equation :
where :
t(I)
= Actual trip time delay when the input current equals
I
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.
The constants
A
,
B, K
and
a
have different values for the different Time Current Curves.
Curve Name
Curve Identifier
A
B
a
K
IEC A Inverse
A
0.14
0
0.02
0.3366
IEC B Very Inverse
B
13.5
0
1
0.6667
IEC C Extr. Inverse
C
80
0
2
1.2375
IEEE Moderate Inverse
MI
0.0104
0.0226
0.02
4.1106
IEEE Short Inverse
SI
0.00342
0.00262
0.02
13.3001
IEEE Very Inverse
VI
3.88
0.0963
2
7.3805
IEEE Inverse
I
5.95
0.18
2
4.1649
IEEE Extremely Inverse
EI
5.67
0.0352
2
10.814
Independent Definite time
D
t = Ts
Curves are user selectable for the following relay’s functions
1F51
(FI>)
= Low-set phase overcurrent
1F51N
(FO>)
= Low-set Earth Fault current
F46
(FI
2
>)
= Negative Sequence overcurrent
For functions
2F51
(I>>, tI>>)
= High-set phase overcurrent
2F51N
(O>>, tO>>) = High -set Earth Fault current
the operation is Independent Definite time only
1
a
B
1
10
A
10
I
I
s
