ABB Relion 620 Series - Page 626

Figure 329: MNSPTOC Inverse Curve A
If the negative sequence current drops below the Start value setting, the reset time
is defined as:
t s a
b
[ ]
= ×






100
(Equation 131)
t[s] Reset time in seconds
a set Cooling time
b
percentage of start time elapse ( START_DUR)
When the reset period is initiated, the time for which START has been active is
saved. 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. If the reset period elapses without a fault being detected, the operate
timer is reset and the saved values of start time and integration are cleared.
Inv. curve B
The inverse time equation for curve type B is:
t s
k
I
I
I
I
r
S
r
[ ]
=






−






2
2 2
(Equation 132)
t[s]
Operate time in seconds
k Machine time Mult
I
2
Negative-sequence current
Table continues on the next page
Protection functions 1MRS757644 H
626 620 series
Technical Manual