ABB Relion 620 Series - Page 625

are selected, the functionality is only affected by the Operate delay time and Reset
delay time settings.
The protection relay provides two user-programmable IDMT characteristics curves,
"Inv. curve A" and "Inv. curve B".
Current-based inverse definite minimum time curve (IDMT)
In inverse-time modes, the operate time depends on the momentary value of the
current: the higher the current, the shorter the operate time. The operate time
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 130)
t[s] Operate time in seconds
k Set Machine time Mult
I
2
Negative-sequence current
I
r
Set Rated current
1MRS757644 H Protection functions
620 series
Technical Manual
625