Manual

Protection Functions 3-39
865-UM001A-EN-P – July 2009
Table 3.24 – Constants for IEEE/ASI 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
9.11140.0
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 3.23.
Figure 3.20 – ANSI/IEEE Long Time Figure 3.21 – ANSI/IEEE Long Time
Inverse Delay Very Inverse Delay