Technical description
2 Protection functions
2.23 Inverse time operation
VM50.EN004
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103
Table 2.23.1-3 Constants for IEEE/ANSI inverse delay equation
Parameter
Delay type
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
.
1
1140
.
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 2.23.1-8.
Figure 2.23.1-5 ANSI/IEEE long
time inverse delay
Figure 2.23.1-6 ANSI/IEEE long
time very inverse delay