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Figure 2-30
1
)
if phase-segregated auxiliary contacts are available
2
)
if series-connected NC contacts are available
On the other hand, current flow is not a reliable criterion for proper operation of the circuit breaker for faults
which do not cause detectable current flow (e.g. Buchholz protection). Information regarding the position of the
circuit breaker auxiliary contacts is required in these cases to check the correct response of the circuit breaker.
For this purpose, the binary input „>BF Start w/o I" No. 1439 is provided (Figure 2-32 left). This input
initiates the breaker failure protection even if no current flow is detected.
Common phase initiation
Common phase initiation is used, for example, in systems with only three-pole tripping, for transformer feeders,
or if the busbar protection trips. This is the only available initiation mode if the actual 7VK61 model can only trip
three-pole.
If the breaker failure protection is intended to be initiated by further external protection devices, it is recom-
mended, for security reasons, to connect two binary inputs to the device. Besides the trip command of the ex-
ternal protection to the binary input „>BF Start 3pole" no. 1415 it is recommended to connect also the
general device pickup to binary input „>BF release" no. 1432. For Buchholz protection it is recommended
that both inputs are connected to the device by two separate wire pairs.
Nevertheless, it is possible to initiate the breaker failure protection in single-channel mode should a separate
release criterion not be available. The binary input „>BF release" (No. 1432) must then not be assigned to
any physical input of the device during configuration.
Figure 2-32 shows the operating principle. When the trip signal appears from any internal or external feeder
protection and at least one current flow criterion according to Figure 2-29 is present, the breaker failure protec-
tion is initiated and the corresponding delay time(s) is (are) started.
If the current criterion is not fulfilled for any of the phases, the position of the circuit breaker auxiliary contact
can be queried as shown in Figure 2-31. If the circuit breaker poles have individual auxiliary contacts, the series
connection of the three normally closed (NC) auxiliary contacts is used. After a three-pole trip command the
circuit breaker has only operated correctly if current no longer flows over the poles or if all three NC auxiliary
contacts are closed.
Figure 2-31 illustrates how the internal signal „CB pole ≥ L1 closed" is created (see Figure 2-32 left) if at least
one circuit breaker pole is closed.
With binary input 1424 „>BF STARTonlyT2" the trip delay time 3906 T2 can be started. After this time has
elapsed, the breaker failure trip command 1494 „BF T2-TRIP(bus)" is generated.
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009
Interlock of the auxiliary contact criterion - example for phase L1
2.6 Circuit breaker failure protection (optional)
Functions
117
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