2 Functions
180
7SD610 Manual
C53000-G1176-C145-4
Figure 2-64 Interlock of the auxiliary contact criterion - example for phase L1
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 pro-
tection). 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 2-66
left). This input initiates the breaker failure protection even if no current flow is detect-
ed.
Common phase
initiation
Common phase initiation is used, for example, in systems with only three-pole trip-
ping, for transformer feeders, or if the busbar protection trips. This is the only available
initiation mode if the actual 7SD610 model can only trip three-pole.
If the breaker failure protection is intended to be initiated by further external protection
devices, it is recommended, 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 recom-
mended 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 2-66 shows the operating principle. When the trip signal appears from any in-
ternal or external feeder protection and at least one current flow criterion according to
Figure 2-63 is present, the 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 2-65. 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 2-65 illustrates how the internal signal „CB pole ≥L1 closed“ is created (see
Figure 2-66 left) if at least one circuit breaker pole is closed.
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