Ri And Rxidg Type Inverse Time Operation - Allen-Bradley Rockwell Automation 857 User Manual

3-88
Protection Functions
857-UM001A-EN-P – July 2009
Figure 3.52 – IEEE2 Very 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 3.7 and
Equation 3.8. 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 relay for real time usage.
Equation 3.7 – RI
=
t
RI
−
. 0 339
Figure 3.53 – IEEE2 Extremely
k
. 0 236
⎛ ⎞
I
⎜ ⎟
⎜ ⎟
I
⎝ ⎠
pickup
Inverse Delay