Siemens SIPROTEC 7SA522 Manual page 237

7SA522 Manual
C53000-G1176-C155-3
located on the line side of the circuit breaker or that facilities for transfer of a close
command to the remote line end exists.
Figure 2-101 shows an example with voltage measurement. It is assumed that the
device I is operating with defined dead times whereas the adaptive dead time is con-
figured at position II. It is important that the line is at least fed from busbar A, i.e. the
side with the defined dead times.
With the adaptive dead time the automatic reclosure function at line end II decides in-
dependently if and when reclosure is sensible and allowed and when it is not. The cri-
terion is the line voltage at end II, which was re-applied from end I following reclosure
there. Reclosure therefore takes place at end II as soon as it is apparent that voltage
has been re-applied to the line from end I.
In the illustrated example, the lines are disconnected at positions I, II and III. At I re-
closure takes place after the parameterized dead time. At III a reduced dead time can
take place (see above) if there is also an infeed on busbar B.
If the fault has been cleared (successful reclosure), line A - B is re-connected to the
voltage at busbar A through position I. Device II detects this voltage and also recloses
after a short delay (to ensure a sufficient voltage measuring time). The fault is cleared.
If the fault has not been cleared after reclosure at I (unsuccessful reclosure), a switch
on to fault occurs at I, no healthy voltage appears at II. The device there detects this
and does not reclose.
In the case of multiple reclosure the sequence may be repeated several times follow-
ing an unsuccessful reclosure until one of the reclosures attempts is successful or a
final trip takes place.
Figure 2-101 Example of adaptive dead time (ADT)
As is shown by the example, the adaptive dead time has the following advantages:
• The circuit-breaker at position II is not reclosed at all if the fault persists and is not
unnecessarily stressed as a result.
• With non-selective tripping by overreach at position III no further trip and reclose
cycles occur here because the short-circuit path via busbar B and position II
remains interrupted even in the event of several reclosure attempts.
• At position I overreach is allowed in the case of multiple reclosures and even in the
event of final tripping because the line remains open at position II and therefore no
actual overreach can occur at I.
The adaptive dead time also includes the reduced dead time because the criteria are
the same. There is no need to set the reduced dead time as well.
2.13 Automatic reclosure function (optional)
237