VAMP 265 - LTI Long Time Inverse; NI1 Normal Inverse; Very Inverse; EI Extremely Inverse

Technical description
2 Protection functions
2.13 Inverse time operation
VM265.EN011
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85
Equation 2.13.1-1
1









B
pickup
I
I
Ak
t
t = Operation delay in seconds
k = User‟s multiplier
I = Measured value
Ipickup = User‟s pick up setting
A, B = Constants parameters according Table.
There are three different delay types according IEC 60255-3,
Normal inverse (NI), Extremely inverse (EI), Very inverse (VI)
and a VI extension, Long time inverse (LTI).
Table 2.13.1-2 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