VAMP 265 - Page 90

2.13 Inverse time operation
2 Protection functions
Technical description
90
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VM265.EN011
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 2.13.1-2, which in VAMP
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 2.13.1-1.
The old electromechanical induction disc relays have inverse
delay for both trip and release operations. However, in VAMP
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 2.13.1-2. 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 2.13.1-2












































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 = Constant parameter according Table 2.13.1-1.
Table 2.13.1-1 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