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3-86
Protection Functions
857-UM001A-EN-P – July 2009
IEEE2 Inverse Time Operation
Before the year 1996 and ANSI standard C37.112, microprocessor
relays were using equations approximating the behavior of various
induction disc type relays. A quite popular approximation is
Equation 8, which in Allen-Bradley device is called IEEE2. Another
name could be IAC, because the old General Electric IAC relays
have been modeled using the same equation.
There are four different delay types according Table 3.53. The old
electromechanical induction disc relays have inverse delay for both
trip and release operations. However, in Allen-Bradley device only
the trip time is inverse, the release time being constant.
The operation delay depends on the measured value and other
parameters according Equation 3.6. Actually this equation can only
be used to draw graphs or when the measured value I is constant
during the fault. A modified version is implemented in the relay for
real time usage.
Equation 3.6
⎡
⎢
⎢
=
+
⎢
t
k
A
⎛
⎢
⎜
⎜
⎢
⎝
⎣
t
=
k
=
I
=
I
=
pickup
A,B,C,D
=
Table 3.53 – Constants for IEEE2 Inverse Delay Equation
Delay type
MI
Moderately inverse
NI
Normally inverse
VI
Very inverse
EI
Extremely inverse
B
D
+
⎞
⎛
I
⎟
I
−
⎜
−
C
⎟
⎜
I
⎠
I
⎝
pickup
pickup
Operation delay in seconds
User's multiplier
Measured value
User's pick up setting
Constant parameter according Table 3.53
A
0.1735
0.6791
0.0274
2.2614
0.0615
0.7989
0.0399
0.2294
E
+
2
3
⎞
⎛
⎞
I
⎟
⎜
⎟
−
C
C
⎟
⎜
⎟
I
⎠
⎝
⎠
pickup
Parameter
B
C
D
0.8
-0.08
0.3
-.1899
0.34
-0.284
0.5
3.0094
⎤
⎥
⎥
⎥
⎥
⎥
⎦
E
0.1271
9.1272
4.0505
0.7222
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