VAMP 52 - Page 101

Technical description 2 Protection functions 2.23 Inverse time operation
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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
14.050.0
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.