Siemens siprotec 7SD5 User Manual page 293

If none of the cycles is successful, the short-circuit protection initiates a final three-pole
trip after the last permissible reclosure, following a protection stage active without
auto-reclosure. The automatic reclosure is blocked dynamically (see also margin
heading „Reclose Block", above).
Handling Evolving When single-pole and single-and three-pole reclose cycles are executed in the net-
Faults work, particular attention must be paid to sequential faults.
Sequential faults are faults which occur during the dead time after clearance of the first
fault.
There are various ways of handling sequential faults in the 7SD5 depending on the
requirements of the network:
For the Detection of an evolving fault you can select whether the trip command of a
protective function during the dead time or every further pickup is the criterion for an
evolving fault.
There are also various selectable possibilities for the response of the internal auto-
reclose function to a detected evolving fault.
• EV. FLT. MODE Stops AutoRecl:
• EV. FLT. MODE starts 3p AR:
If reclosure is blocked due to a sequential fault without the protection issuing a three-
pole trip command (e.g. for sequential fault detection with starting), the device can
send a three-pole trip command so that the circuit breaker does not remain open with
one pole (forced three-pole coupling).
Forced Three-pole If reclosure is blocked during the dead time of a single-pole cycle without a three-pole
Trip trip command having been initiated, 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. You can achieve by a setting param-
eter that the tripping logic of the device sends immediately a three-pole trip command
in this case. This forced three-pole trip pre-empts the pole discrepancy supervision of
the CB because the forced three-pole trip of the device is initiated as soon as the re-
closure is blocked following a single-pole trip or if the CB auxiliary contacts report an
implausible breaker state.
When different internal protection functions of the device initiate a single-pole trip in
different phases, the device will issue a three-pole trip command due to the tripping
logic of the entire device (Section 2.23.1), independent of this forced three-pole trip
function. This is true also for trip commands given via the direct local trip inputs (Sec-
7SD5 Manual
C53000-G1176-C169-1
The reclosure is blocked as soon as an evolving fault is detected. Tripping as a
result of the sequential fault is three-pole. This applies irrespective of whether three-
pole cycles are permitted or not. There are no further reclosure attempts; the auto-
reclosure is blocked dynamically (see also margin heading „Reclose Block",
above).
As soon as a sequential fault is detected the recloser switches over to a three-pole
reclose cycle. All trip commands are now three-pole. The separately settable dead
time for sequential faults starts with the clearance of the sequential fault; after the
dead time the circuit breaker receives a close command. The further sequence is
the same as for single and three-pole cycles.
The complete dead time in this case consists of the portion of the single-pole dead
time up to clearance of the sequential fault plus the dead time for the sequential
fault. This makes sense because the duration of the three-pole dead time is most
important for the stability of the network.
2.15 Automatic Reclosure Function (optional)
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