Siemens SIPROTEC 7UT613 series Manual page 270

2 Functions
Initiation
Delay Time and
Breaker Failure Trip
270
busbar side is supervised. The adjacent circuit breakers are those of the busbar illus-
trated.
With generators the breaker failure protection usually affects the network breaker. In
cases other than that, the supply side must be the relevant one.
The breaker failure protection can be initiated by internal protective functions of the
7UT613/63x, i.e. trip commands of protective functions or via CFC (internal logic func-
tions), or by external trip signals via a binary input. Both sources are processed in the
same way but separately annunciated.
The breaker failure protection checks now the continuation of current flow through the
breaker to be monitored. Additionally, the breaker position (read from the feedback of
the auxiliary contacts) is checked provided associated feedback information is avail-
able.
The current criterion is met if at least one of the three phase currents exceeds a set-
table threshold, e.g. PoleOpenCurr.S1 if the breaker failure protection is assigned
(see also Subsection 2.1.4 under margin heading „Circuit Breaker Status". Special fea-
tures detect the instant of current interruption. In case of sinusoidal currents the
current interruption is detected after approximately
current components in the fault current and/or in the current transformer secondary
circuit after interruption (e.g. current transformers with linearized core), or saturation
of the current transformers caused by the DC component in the fault current, it can
take one AC cycle before the interruption of the primary current is reliably detected.
Evaluation of the breaker auxiliary contacts is carried out only when no current flow is
detected at the instant of initiation, i.e. the trip command of a protection function (in-
ternal or external) which is to start the breaker failure protection. In this case the
breaker is assumed to be open as soon as the auxiliary contact criterion indicates
open breaker.
Once the current flow criterion has picked up before the trip signal from the initiating
protection, the circuit breaker is assumed to be open as soon as the current disap-
pears, even if the associated auxiliary contact does not (yet) indicate that the circuit
breaker has opened. This gives preference to the more reliable current criterion and
avoids false operation due to a defect e.g. in the auxiliary contact mechanism or cir-
cuit. If the auxiliary contacts indicate open breaker even though current is flowing, an
alarm is given (FNos 30135 to 30144).
If both positions of the breaker are indicated (NO contact and NC contact via double
point indication) the auxiliary contact criterion is not evaluated if, at the instant of initi-
ation, an intermediate position is indicated, but only the current criterion. On the other
hand, if the breaker failure protection is already started, the breaker is assumed to
have opened as soon as it is no longer indicated as closed, even if it is actually in in-
termediate position.
Initiation can be blocked via the binary input „>BLOCK BkrFail" (No 047.2404 (e.g.
during test of the feeder protection relay).
The breaker failure protection can be operated single-stage or two-stage
With single-stage breaker failure protection, the trip command is routed to the adjacent
circuit breakers should the local feeder breaker fail. The adjacent circuit breakers are
all those which must trip in order to interrupt the fault current, i.e. the breakers which
feed the busbar or the busbar section to which the feeder under consideration is con-
nected.
1
/ AC cycle. With aperiodic DC
2
7UT613/63x Manual
C53000-G1176-C160-2