VAMP 259 - Page 141

Technical description
2 Protection functions
2.24 Inverse time operation
VM259.EN007
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141
Figure 2.24.1-13 IEEE2 very inverse
delay
Figure 2.24.1-14 IEEE2 extremely
inverse delay
RI and RXIDG type inverse time operation
These two inverse delay types have their origin in old ASEA
(nowadays ABB) earth fault relays.
The operation delay of types RI and RXIDG depends on the
measured value and other parameters according Equation
2.24.1-4 and Equation 2.24.1-5. Actually these equations can
only be used to draw graphs or when the measured value I is
constant during the fault. Modified versions are implemented
in the device for real time usage.
Equation 2.24.1-4. RI










pickup
RI
I
I
k
t
236.0
339.0
Equation 2.24.1-5 RXIDG
pickup
RXIDG
Ik
I
t ln35.18.5 
t = Operation delay in seconds
k = User‘s multiplier
I = Measured value
I
pickup
= User‘s pick up setting