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Technical description
2 Protection functions
2.23 Inverse time operation
VM50.EN004
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101
and a VI extension. Additional there is a de facto standard
Long time inverse (LTI).
Table 2.23.1-2 Constants for IEC inverse delay equation
Parameter
Delay type
A B
NI Normal
inverse
0.14
0.02
EI Extremely
inverse
80
2
VI Very
inverse
13.5
1
LTI
Long time inverse
120
1
Example for Delay type "Normal inverse (NI) ":
k
=
0.50
I
= 4 pu (constant current)
I
pickup
= 2 pu
A
=
0.14
B
=
0.02
0
.
5
1
2
4
14
.
0
50
.
0
02
.
0
t
The operation time in this example will be 5 seconds. The same
result can be read from Figure 2.23.1-1.
Figure 2.23.1-1 IEC normal inverse
delay.
Figure 2.23.1-2 IEC extremely
inverse delay.