VAMP 50, Operation And Configuration Manual

Page: 105 / 232

Technical description 2 Protection functions 2.23 Inverse time operation
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105
There are four different delay types according
Table 2.23.1-4. The old electromechanical induction disc relays
have inverse delay for both trip and release operations.
However, in VAMP relays only the trip time is inverse the
release time being constant.
The operation delay depends on the measured value and other
parameters according Equation 2.23.1-3. 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 relay for real time usage.
Equation 2.23.1-3











































 
3 2
C
I
I
E
C
I
I
D
C
I
I
B
A k t
pickup pickup
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 2.23.1-4.
Table 2.23.1-4 Constants for IEEE2 inverse delay equation
Parameter
Delay type
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
Example for Delay type "Moderately inverse (MI)":
k
= 0.50
I = 4 pu
I
pickup
= 2 pu
A = 0.1735
B = 0.6791
C = 0.8
D = -0.08
E = 0.127