REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-287
Tripping delays t1 and t2
The tripping delay settings enable the BFP to be adapted to its
particular operating environment (e.g. circuit-breaker character-
istics etc.). Fig. 3.5.28.1 shows a typical timing diagram for
clearing a fault.
Tripping time
t
CB open
Delay t1
Delay t2
t
Reset
+ t
Margin
t
CB open
t
Reset
+ t
Margin
Start (2)
CB
open (3)
Repeat
trip (4)
CB
open (5)
Backup
trip (6)
Fault
incidence (1)
Fig. 3.5.28.1 Operation of the BFP/UT timers t1 and t2
Timing in the case of breaker failure:
(1) A fault has occurred and been detected by a protective de-
vice.
(2) A tripping command is transmitted to the circuit-breaker
after the unit protection operating time which also starts the
BFP. The tripping command can be either single (Start Lx)
or three-phase (Start L1L2L3). The redundant signals are
also activated at the same time.
(3) The circuit-breaker ruptures the fault current.
(4) After the reset delay t
Reset
plus a safety margin t
Margin
, the
BFP either detects that the fault current has been inter-
rupted and the protection function resets, or the fault cur-
rent continues to flow and a second attempt is made by the
BFP to trip the circuit-breaker.
(5) The second attempt to trip the circuit-breaker is successful
and the fault current is interrupted.
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