ABB RED615 Technical Manual page 468

Section 4
Protection functions
462
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:
k
[ ]
t s =
2
 
I
2
 
I
 
r
GUID-D8A4A304-6C63-4BA4-BAEA-E7891504557A V1 EN
t[s] Operate time in seconds
Machine time Mult
k Set
I Negative-sequence current
2
Rated current
I Set
r
If the negative-sequence current drops below the Start value setting, the reset time
is defined as:
b
 
[ ]
t s = × a
 
100
 
GUID-8BE4B6AC-FB61-4D30-B77B-3E599D5BAE81 V1 EN
t[s] Reset time in seconds
Cooling time
a set
b percentage of start time elapse (START_DUR)
When the reset period is initiated, the time for which START has been active is
saved. Now, if the fault reoccurs, that is, the negative-sequence current rises above
the set value during the reset period, the operate calculations are continued using
the saved values. However, if the reset period elapses without a fault being
1YHT530004D05 D
(Equation 69)
(Equation 70)
615 series
Technical Manual