Rockwell Automation 865 Differential Protection Relay - Manual (Page 80)

3-36 Protection
Functions
865-UM001A-EN-P – July 2009
Table 3.22 – Available Standard Delay Families and Types
Curve family
Delay type
DT IEC
IEEE IEEE2
RI
DT Definite time X
NI1 Normal inverse X X
VI Very inverse X X X
EI Extremely inverse X X X
LTI Long time inverse X X
LTEI Long time extremely inverse X
LTVI Long time very inverse X
MI Moderately inverse X X
STI Short time inverse X
STEI Short time extremely inverse X
RI Old ASEA type X
RXIDG Old ASEA type X
IEC Inverse Time Operation
The operation time depends on the measured value and other
parameters according Equation 6. 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 6
1 −
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
B
pickup
I
I
A k
t
t = Operation delay in seconds
k = User’s multiplier
I = Measured value
I pickup = User’s pick up setting
A, B = Constants parameters according Table 3.23.
There are three different delay types according IEC 60255-3, Normal
inverse (NI), Extremely inverse (EI), Very inverse (VI) and a VI
extension, Long time inverse (LTI).