Siemens Siprotec 7VK61 Manual page 51

Figure 2-6
A, B, C
I, II, III
X
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 (or ends). This requires the voltage
transformers to be connected to the device and to be located on the line side of the circuit breaker. This func-
tionality is only available if the device is connected across three voltage transformers.
Figure 2-7 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 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.
With the adaptive dead time, the automatic reclosure function at line end II decides independently if and when
reclosure is sensible and allowed and when it is not. The criterion 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. All phase-to-phase and phase-to-earth voltages are
monitored.
In the illustrated example, the lines are disconnected at positions I, II and III. At I reclosure 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 mea-
suring 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 following an unsuccessful reclo-
sure until one of the reclosures attempts is successful or a final trip takes place.
Figure 2-7
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009
Example of a reduced dead time (RDT)
Busbars
Relay locations
Tripped circuit breakers
Example of adaptive dead time (ADT)
2.2 Automatic reclosure function (optional)
Functions
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