VAMP 259 - Page 135

Technical description
2 Protection functions
2.24 Inverse time operation
VM259.EN007
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135
Table 2.24.1-2 Constants for IEC inverse delay equation
Delay type
Parameter
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 2.24.1-1.
Figure 2.24.1-1 IEC normal inverse
delay.
Figure 2.24.1-2 IEC extremely inverse
delay.