Rockwell Automation 865 Differential Protection Relay - Manual (Page 87)

Protection Functions 3-43
865-UM001A-EN-P – July 2009
Figure 3.28 – IEEE2 Very Inverse Delay Figure 3.29 – IEEE2 Extremely
Inverse Delay
RI and RXIDG type Inverse Time Operation
These two inverse delay types have their origin in old ASEA (ABB)
earth fault relays.
The operation delay of types RI and RXIDG depends on the
measured value and other parameters according Equation 9 and
Equation 10. 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 9 – RI
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
=
pickup
RI
I
I
k
t
236 . 0
339 . 0