ABB RELION REX640 Technical Manual page 766

Section 4
Protection functions
760
calculation or integration starts immediately when the current exceeds the set Start
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 settings define 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:
k
t s
[ ]
=
2
I
 
2
 
I
 r 
GUID-4CA25794-D742-4FAD-A8C9-4E910D8B04AD V1 EN
t[s] Operate time in seconds
Machine time Mult
k Set
I Negative-sequence current
2
Rated current
I Set
r
1MRS759142 C
(Equation 191)
REX640
Technical Manual