Micom P721, Technical Manual

Page: 164 / 334

P72x/EN AP/C21 Application Guide
Page 28/52 MiCOM P721/P723
3.4 Circuit breaker failure
The P72x has one circuit breaker failure function. The current considered by the CBF
function is the differential current, therefore the current flowing through a particular circuit
breaker is not considered. If the CBF function in the P72x is asserted and the breaker is still
closed, the 86BF associated to that particular breaker should be energized. Meanwhile the
86BF associated to the other breakers should not be energized. This is done by wiring one
52a contact in the 86BF circuit of each breaker in the high impedance scheme. Consider the
single busbar scheme shown in FIGURE 26.
- - -
-
86BF1
50BF-P72x
BK1- 52a
+
86BF2
50BF-P72x
BK2- 52a
+
86BF3
50BF-P72x
BK3- 52a
+
86BF4
50BF-P72x
BK4- 52a
+
b) 86BF-x circuits
BUS
VTs
BK4 BK3
1 2
4 3
BK2 BK1
a) Single busbar
P4496ENa
FIGURE 26: CIRCUIT BREAKER FAILURE APPLICATION