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7SV512
V1
4.2.3
Processing of the circuit breaker auxiliary contacts
Current flow is not a reliable criterion for proper oper-
ation of the circuit breaker for faults which do not
cause detectable current flow (e.g. Buchholz pro-
tection). Information about the position of the circuit
breaker auxiliary contacts is required in these cases
to check correct response of the circuit breaker. If
the breaker poles can be switched individually, infor-
mation about the position of each individual circuit
breaker pole is useful (but not always a precondi-
tion).
The relay incorporates a circuit breaker position log-
ic (Figure 4.7), which offers various possibilities, de-
pendent of which auxiliary contacts are available
from the circuit breaker and how they are connected
to binary inputs of the relay.
If the circuit breaker is switched only three-pole, its
auxiliary contact is connected to a binary input mod-
ule which is assigned to the input function ">CB
Aux. 1p C" (BI 20 in Figure 4.7). The remaining
inputs in the figure are not used then.
If the circuit breaker poles can be switched individu-
ally but only the parallel connected auxiliary con-
tacts are available, then the binary input for this con-
nection must be assigned exclusively to the input
function ">CB Aux. 1p C" (BI 20 in Figure 4.7).
The remaining inputs in the figure are not used then.
If the circuit breaker poles can be switched individu-
ally and each individual auxiliary contact is available
then it is recommended to connect the auxiliary con-
tact of each individual pole to an individual binary in-
put. This connection allows maximum information to
be processed in the relay. The assignment of the
binary inputs is as follows:
--- auxiliary contact of pole L1 assigned to input func-
tion ">CB Aux. L1" (BI 16 in Figure 4.7),
--- auxiliary contact of pole L2 assigned to input func-
tion ">CB Aux. L2" (BI 17 in Figure 4.7),
--- auxiliary contact of pole L3 assigned to input func-
tion ">CB Aux. L3" (BI 18 in Figure 4.7).
Binary inputs BI 19 and BI 20 are not used in this
case. This connection mode is recommended if the
breaker failure protection can be initiated by a feeder
protection function which may trip at low-current or
no-current conditions and which shall operate in
conjunction with single-pole auto-reclosure (e.g.
weak-infeed trip with carrier transmission).
C53000---G1176---C91
If the circuit breaker poles can be switched individu-
ally but only two binary inputs can be used, one can
connect the parallel connection of one set of auxilia-
ry contacts to a binary input and the series connec-
tion to another. The inputs are assigned to the func-
tion ">CB Aux. 1p C" (BI 20 in Figure 4.7) for the
parallel connection and to ">CB Aux. 3p C" (BI 19
in Figure 4.7) for the series connection. A single-pole
trip command is assumed to be executed, when the
series connection is interrupted.
Note that Figure 4.7 shows the total logic for all the
connection possibilities. In the actual case a part of
the inputs and logic is only used, as described
above.
The 8 outputs of the circuit breaker position logic are
processed by the protection functions. The output
signals are blocked as long as the input signals are
not plausible: e.g. a circuit breaker pole cannot be
open and closed at the same time.
Evaluation of the breaker auxiliary contacts is car-
ried out in the breaker failure protection function only
as long as the current flow monitoring has not
picked up. Once the current flow criterion has been
detected during trip signal of the protection, the cir-
cuit breaker is assumed to be open as soon as the
current has disappeared, even when the associated
auxiliary contact does not (yet) indicate that the cir-
cuit breaker has opened (Figure 4.6). This gives
preference to the more reliable current criterion and
avoids overfunctioning due to a defect e.g. in the
auxiliary contact mechanism or circuit. This interlock
feature is provided for each individual phase as well
as for three-pole trip; in the latter case the "any pole
closed" output as illustrated in Figure 4.7 is decisive
for the "CB aux. contact" signal of Figure 4.6.
current
&
flow
prot.
trip
CB aux.
contact
Figure 4.6
Interlock of the auxiliary contact cri-
terion
Method of operation
S Q
Auxiliary
contact
R
criterion
&
Aux
27
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