VAMP 259 - Page 139

Technical description
2 Protection functions
2.24 Inverse time operation
VM259.EN007
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139
IEEE2 inverse time operation
Before the year 1996 and ANSI standard C37.112
microprocessor relays were using equations approximating the
behaviour of various induction disc type relays. A quite
popular approximation is Equation 2.24.1-3, which in VAMP
devices 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 2.24.1-4.
The old electromechanical induction disc relays have inverse
delay for both trip and release operations. However, in VAMP
devices only the trip time is inverse the release time being
constant.
The operation delay depends on the measured value and other
parameters according
Equation 2.24.1-3. 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 device for
real time usage.
Equation 2.24.1-3
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

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
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

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






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32
C
I
I
E
C
I
I
D
C
I
I
B
Akt
pickuppickup
pickup
t = Operation delay in seconds
k = User‘s multiplier
I = Measured value
I
pickup
= User‘s pick up setting
A,B,C,D,E = Constant parameter according Table 2.24.1-4.
Table 2.24.1-4 Constants for IEEE2 inverse delay equation
Delay type
Parameter
A
B
C
D
E
MI
Moderately inverse
0.1735
0.6791
0.8
-0.08
0.1271
NI
Normally inverse
0.0274
2.2614
0.3
-.1899
9.1272
VI
Very inverse
0.0615
0.7989
0.34
-0.284
4.0505
EI
Extremely inverse
0.0399
0.2294
0.5
3.0094
0.7222