ABB RELION REX640 Technical Manual page 844

Protection functions
calculation or integration starts immediately when the current exceeds the set
value and the START output is activated.
The OPERATE output of the component is activated when the cumulative sum of the
integrator calculating the overcurrent situation exceeds the value set by the inverse
time mode. The set value depends on the selected curve type and the setting values
used.
The
minimum operate time and maximum operate time possible for the IDMT mode.
For setting these parameters, a careful study of the particular IDMT curves is
recommended.
Inv. curve A
The inverse time equation for curve type A is:
[ ]
t s
t[s]
k
I
2
I
r
844
Minimum operate time and Maximum operate time settings define the
k
=
2
 
I
2
 
I
 
r
Operate time in seconds
Machine time Mult
Set
Negative-sequence current
Rated current
Set
1MRS759142 F
Start
(Equation 237)
REX640
Technical Manual