ABB RELION 620 Series Technical Manual page 254

Section 4
Protection functions
248
If the negative sequence current drops below the Pickup 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 pickup time elapse (PICKUP_DUR)
When the reset period is initiated, the time for which PICKUP 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 trip calculations are continued using the saved values. If the reset
period elapses without a fault being detected, the trip timer is reset and the saved values
of pickup time and integration are cleared.
Inv. curve B
The inverse time equation for curve type B is:
k
[ ]
t s =
2 2
   
I I
2 S
 −
  
I I
   
r r
GUID-805DCB50-71D2-4721-830B-3343E1A5500B V1 EN
t[s] Trip time in seconds
Machine time Mult
k
I Negative-sequence current
2
Pickup value
I Set
S
Rated current
I Set
r
If the fault disappears, the negative-sequence current drops below the Pickup value setting
and the PICKUP output is deactivated. The function does not reset instantaneously.
Resetting depends on the equation or the Cooling time setting.
The timer is reset in two ways:
• When the negative sequence current drops below pickup value, the subtraction in the
denominator becomes negative and the cumulative sum starts to decrease. The
decrease in the sum indicates the cooling of the machine and the cooling speed
1MAC504801-IB E
(Equation 6)
(Equation 7)
620 series ANSI
Technical Manual