Woodward
Manual MRIK3-C EN
48
DOK-TD-MRIK3-C Rev. A
6.7.4
CB
failure
protection
The CB failure protection is based on supervision of phase currents during tripping events. Only af-
ter tripping this protective function becomes active. The test criterion is whether all phase currents
are dropped to <1% x I
N
within t
CBFP
(Circuit Breaker Failure Protection - adjustable between
0.1 - 2.0 s). If not all of the phase currents have dropped to <1%xI
N
within this time, CB failure is
detected and the related relay activated. The CB failure protection function is deactivated again as
soon as the phase currents have dropped to 0 within t
CBFP
.
6.7.5
Release of the pickup relay for CB failure protection
This function is working similar to the Block / Trip function. In the case of a fault the function is acti-
vated. The pickup is indicated via a alarm relay to the upstream CB protection unit. At the upstream
CB protection unit the blocking input is activated. During the clearing of the fault a CB failure take
place, the alarm relay switch off after the settable CB failure time (Chap 6.7.4) and clear the block
input of the upstream protection unit and activated the tripping.
Figure 6.5:
I>
+
+
+
tI>
t
1
0
tI>
t
1
0
I>
t
CBFP
Protection Block
Trip
Block
t
1
0
