ABB RELION REX640 - Page 844

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:
t s
k
I
I
r
[ ]
=






2
2
(Equation 237)
t[s] Operate time in seconds
k Set Machine time Mult
I
2
Negative-sequence current
I
r
Set Rated current
Protection functions 1MRS759142 F
844 REX640
Technical Manual