Functions
2.17 Automatic Reclosure Function (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
326
If reclosure is blocked due to a sequential fault without the protection issuing a 3-pole trip command (e.g. for
sequential fault detection with starting), the device can send a 3-pole trip command so that the circuit breaker
does not remain open with one pole (forced 3-pole trip).
Forced 3-pole trip
If reclosure is blocked during the dead time of a 1-pole cycle without a 3-pole trip command having been initi-
ated, the breaker would remain open at one pole. In most cases, the circuit breaker is equipped with a pole
discrepancy supervision which will trip the remaining poles after a few seconds. By setting a parameter, you
can achieve that the tripping logic of the device immediately sends a 3-pole trip command in this case. This
forced 3-pole trip pre-empts the pole discrepancy supervision of the CB because the forced 3-pole trip of the
device is initiated as soon as the reclosure is blocked following a 1-pole trip or if the CB auxiliary contacts report
an implausible breaker state.
When different internal protection functions initiate a 1-pole trip in different phases, the device will issue a 3-
pole trip command due to the tripping logic (Section 2.25.1), independent of this forced 3-pole trip. This is also
true for trip commands given via the direct local trip inputs (Section 2.12) or the reception of a remote trip (Sec-
tion 2.13) since these signals directly affect the tripping logic of the device.
If the device trips 1-pole and if an external trip command in another phase only reaches the device via one of
the binary inputs, e.g.
„>Trip L1 AR“
to the internal automatic reclosure function, this is not routed to the
tripping logic. In this case, 3-pole trip is ensured only if the forced 3-pole trip is effective.
The forced 3-pole trip is also activated when only 3-pole cycles are allowed, but a 1-pole trip is signalled exter-
nally via a binary input.
Dead Line Check (DLC)
If the voltage of a disconnected phase does not disappear following a trip, reclosure can be prevented. A pre-
requisite for this function is that the voltage transformers are connected on the line side of the circuit breaker.
To select this function the dead line check must be activated. The automatic reclosure function then checks the
disconnected line for no-voltage: the line must have been without voltage for at least an adequate measuring
time during the dead time. If this was not the case, the reclosure is blocked dynamically.
This no-voltage check on the line is of advantage if a small generator (e.g. wind generator) is connected along
the line.
Adaptive Dead Time (ADT)
In all the previous alternatives it was assumed that defined and equal dead times were set at both line ends, if
necessary for different fault types and/or reclose cycles.
It is also possible to set the dead times (for different fault types and/or reclose cycles, if necessary) at one line
end only and to configure the adaptive dead time at the other end(s). This requires that the voltage transformers
are located on the line side of the circuit breaker or that a close command can be sent to the remote line end.
Figure 2-159 shows an example with voltage measurement. It is assumed that device I is operating with defined
dead times whereas the adaptive dead time is configured at position II. It is important that the line is fed at least
from busbar A, i.e. the side with the defined dead times.
With the adaptive dead time the automatic reclosure function at line ends II and III decides independently
whether and when reclosure is useful and permissible and when it is not. The criterion is the line voltage at
ends II and III. Thus, reclosure at ends II and III takes place as soon as it is apparent that voltage has been
applied to the line. All phase-to-phase and phase-to-earth voltages are monitored.
In the illustrated example of a short circuit, the lines are disconnected at positions I, II and III. At I reclosure
takes place after the parameterized dead time. At III the ADT function can be used for a reclosure after a short
delay (to ensure a sufficient voltage measuring time) since the voltage remains if there is also an infeed on
busbar B.
