Siemens SIPROTEC 7SD610 Manual page 133

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 (if necessary different for various fault types and/or reclose cycles) at
one line end only and to configure the adaptive dead time at the other end. This can be done provided that the
voltage transformers are located on the line side of the circuit breaker or that a means for transfer of a close
command to the remote line end exists.
Figure 2-46 shows an example with voltage measurement. It is assumed that device I operates with defined
dead times whereas the adaptive dead time is configured 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.
When using the adaptive dead time, the automatic reclosing function at line end II decides autonomously
whether to allow reclosing or not. Its decision is based on the line voltage at end II, which was reapplied from
end I following reclosure. Device II will thus initiate reclosing as soon as it is evident that the line has been re-
energized from end I. 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, and II. In I reclosure takes
place after the configured dead time.
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 mea-
suring time). The fault is cleared.
If the fault has not been cleared after reclosure at I (unsuccessful reclosure), the line will be disconnected again
in position I with the result that no healthy voltage is detected at location II so that the circuit breaker there does
not reclose.
In the case of multiple reclosure the sequence may be repeated several times following an unsuccessful reclo-
sure until one of the reclosure attempts is successful or a final trip takes place.
Figure 2-46
A, B
I, II
As is shown by the example, the adaptive dead time has the following advantages:
• The circuit breaker at position II is not reclosed if the fault persists and is not unnecessarily stressed as a
result.
• With non-selective tripping outside the protected zone by an overreaching time-graded protection, no further
reclosure cycles can be generated there because the fault current path via busbar B and position II remains
interrupted even after several reclosures.
• 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.
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
Example of adaptive dead time (ADT)
Busbars
Relay locations
2.10 Automatic Reclosure Function (optional)
Functions
133