Manual

Protection Functions 3-37
865-UM001A-EN-P – July 2009
Table 3.23 – 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 3.16.
Figure 3.16 – IEC Normal Inverse Delay Figure 3.17 – IEC Extremely Inverse Delay