VAMP 259 - Page 137

Technical description
2 Protection functions
2.24 Inverse time operation
VM259.EN007
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137
Table 2.24.1-3 Constants for IEEE/ANSI inverse delay equation
Delay type
Parameter
A
B
C
LTI
Long time inverse
0.086
0.185
0.02
LTVI
Long time very inverse
28.55
0.712
2
LTEI
Long time extremely
inverse
64.07
0.250
2
MI
Moderately inverse
0.0515
0.1140
0.02
VI
Very inverse
19.61
0.491
2
EI
Extremely inverse
28.2
0.1217
2
STI
Short time inverse
0.16758
0.11858
0.02
STEI
Short time extremely
inverse
1.281
0.005
2
Example for Delay type "Moderately inverse (MI)":
k = 0.50
I = 4 pu
I
pickup
= 2 pu
A = 0.0515
B = 0.114
C = 0.02
9.11140.0
1
2
4
0515.0
50.0
02.0























t
The operation time in this example will be 1.9 seconds. The
same result can be read from Figure 2.24.1-8.
Figure 2.24.1-5 ANSI/IEEE long
time inverse delay
Figure 2.24.1-6 ANSI/IEEE long
time very inverse delay