94
DMC3S - Manual - 08 - 2021
—
Breaker failure - BF
Preface
Should a fault cause a protection to open the breaker but, due to a fault, the breaker cannot open, the
BF protection opens another or other breaker/s to shut off the fault current.
The BF protection can be started when the relay's internal protection trips, so long as the latter is
mapped to the BF protection, or when an external protection connected to one of the relay's logical
inputs trips.
Operating logic
The BF timer starts when both the following conditions are satisfied:
1) The relay's internal protection functions have started and tripped (BF protection thresholds tripped)
or, if enabled, an external protection mapped to one of the relay's logical inputs has tripped.
2) The state of the breaker's auxiliary contacts 52a and 52b corresponds to breaker closed or the
value of the fundamental component of at least one phase current
I
L1
,
I
L2
,
I
L3
is greater than an ad-
justable threshold
I
BF
> or the fundamental component of the residual current
I
E
is greater than an
adjustable threshold
I
EBF
>. If no information about the state of the breaker is available (e.g.: aux-
iliary contacts not accessible or no free logical inputs on the relay), this control must be disabled.
If the two above conditions persist for the duration of the set operating time
t
BF
>, when the time
expires the BF protection trips, otherwise the timer and protection are both reset.
To reset the BF protection as quickly as possible, following the start of the protection itself (condition
1), the relay's internal protections must not only trip but also start (resetting the start of the protection
functions is faster than resetting their trip).
The protection can be enabled or disabled by setting to
ON
or
OFF
the parameter
BF Enable
in
the menu
Set \ Protections \ Breaker failure - BF
.
Starting BF with a switch:
set to
ON
the parameter
CB Input
, if two logical inputs are configured
to acquire the state of the breaker's auxiliary contacts 52a and 52b, breaker state control is enabled.
Breaker state control is enabled in the menu
Set \ Protections \ Breaker failure - BF
, while the
acquisition of the breaker position is mapped to the logical inputs (
52a
and
52b
) in the menu
Set
\ Input board inputs \ Input IN1-1...IN1-6
.
If no information about the state of the breaker is available,
the control must be disabled by setting to
OFF
the parameter
CB Input
.
All parameters
I
BF>
,
I
EBF
and
t
BF
can be programmed separately; they are available in the menu
Set \
Protections \ Breaker failure - BF.
all-FBF.ai
General block diagram of the breaker failure function (BF)
Block1
BLK1 BF
IL1...IL3
IE
52a/ 52b
Trip ProtE x t
Star t BF
Trip BF
Block1
&
BF-BLK1
BF Enable
IBF>
IEBF>
tBF
TR
IP
PI
NG M
AT
RI
X
(LE
D+R
EL
AY
S)
Start BF
Start IBF>
Trip BF
&
Start BF
ON
≡
CB Closed
Trip BF
52a
52a
I
BF
>
Max
I
L1
...
I
L3
≥
I
BF
>
I
L1
I
L2
I
L3
I
EBF
>
I
E
≥
I
EBF
>
I
E
≥
1
RESET
t
BF
0
T
t
BF
Binary input INx
T
0
Logic
INx
t
ON
INx
t
ON
INx
t
OFF
T
0
n.o.
n.c.
INx
t
OFF
52b
Binary input INx
T
0
Logic
INx
t
ON
INx
t
ON
INx
t
OFF
T
0
n.o.
n.c.
INx
t
OFF
52b
Start IEBF>
“0”
CB Input
CB Input OFF
CB Input ON
Functional diagram of the breaker failure function - BF
