Siemens SIPROTEC 7SD610 Manual page 181

Figure 2-67
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 2-69 left). This input
initiates the circuit breaker failure protection even if no current flow is detected.
Common phase initiation
Common phase initiation is used, for example, in systems with only 3-pole tripping, for transformer feeders, or
if the busbar protection trips. It is the only available initiation mode when using the 7SD610 version capable of
3-pole tripping only.
If the circuit breaker failure protection is intended to be initiated by further external protection devices, it is rec-
ommended, for security reasons, to connect two binary inputs to the device. Besides the trip command of the
external 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 circuit breaker failure protection in single-channel mode should a sep-
arate release criterion not be available. The binary input „>BF release" (No. 1432) must then not be as-
signed to any physical input of the device during configuration.
Figure 2-69 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 2-66 is present, the circuit breaker failure
protection 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 2-68. If the circuit breaker poles have individual auxiliary contacts, the series
connection of the three normally closed (NC) auxiliary contacts is used. After a 3-pole trip command the circuit
breaker has only operated correctly if no current is flowing via any phase or alternatively all three auxiliary con-
tacts indicate the CB is open.
Figure 2-68 illustrates how the internal signal „CB pole ≥L1 closed" is created (see Figure 2-69 left) if at least
one circuit breaker pole is closed.
By means of the binary input 1424 „>BF STARTonlyT2", the tripping delay 3906 T2 can be started. After this
time stage has elapsed, the circuit breaker failure TRIP command 1494 „BF T2-TRIP(bus)" is issued.
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
Interlock of the auxiliary contact criterion - example for phase L1
Functions
2.13 Circuit Breaker Failure Protection
181