Siemens Siprotec 7VK61 Manual page 58

Functions
2.2 Automatic reclosure function (optional)
Adaptive Dead Time (ADT)
When operating with adaptive dead time, it must be ensured in advance that one end per line operates with
defined dead times and has an infeed. The other (or the others in multi-branch lines) may operate with adaptive
dead time. It is essential that the voltage transformers are located on the line side of the circuit breaker. Details
about this function can be found in Section 2.2 at margin heading „Adaptive Dead Time (ADT) and Close
Command-transfer (Remote-CLOSE)".
For the line end with defined dead times the number of desired reclose cycles must be set during the configu-
ration of the protective functions (Section 2.1.1) in address 133 Auto Reclose. For the devices operating
with adaptive dead time Auto Reclose = ADT must be set during the configuration of the protective functions
under address 133. Only the parameters described below are interrogated in the latter case. No settings are
then made for the individual reclosure cycles. The adaptive dead time implies functionality of reduced dead
time.
The adaptive dead time may be voltage-controlled or Remote–CLOSE–controlled. Both are possible at the
same time. In the first case, reclosure takes place as soon as the returning voltage, after reclosure at the remote
end, is detected. For this purpose the device must be connected to voltage transformers located on the line
side. In the case of Remote-CLOSE, the autoreclosure waits until the Remote-CLOSE command is received
from the remote end.
The action time T-ACTION ADT (address 3433) is the timeframe after initiation (fault detection) by any protec-
tive function which can start the automatic reclosure function within which the trip command must appear. If no
trip command is issued until the action time has expired, there is no reclosure. Depending on the configuration
of the protective functions (see Section 2.1.1.2), the action time may also be omitted; this applies especially
when an initiating protective function has no fault detection signal.
The dead times are determined by the reclosure command of the device at the line end with the defined dead
times. In cases where this reclosure command does not appear, e.g. because the reclosure was in the mean-
time blocked at this end, the readiness of the local device must return to the quiescent state at some time. This
takes place after the maximum wait time T-MAX ADT (address 3434). This must be long enough to include the
last reclosure of the remote end. In the case of single cycle reclosure, the sum total of maximum dead time plus
reclaim time of the other device is sufficient. In the case of multiple reclosure the worst case is that all reclosures
of the other end except the last one are unsuccessful. The time of all these cycles must be taken into account.
To save having to make exact calculations, it is possible to use the sum of all dead times and all protection
operating times plus one reclaim time.
At address 3435 ADT 1p allowed it can be determined whether single-pole tripping is allowed (provided that
single-pole tripping is possible). If NO, the protection trips three-pole for all fault types. If YES, the actual trip
signal of the starting protective functions is decisive. If the blocking time is unequal to 0 s and single-pole trip-
ping is allowed, single-pole tripping will be prevented during the blocking time. Each fault is thus disconnected
in three poles while the blocking time expires.
Address 3403 T-RECLAIM allows disabling the blocking time in ADT mode. In doing so, the ADT cycle includ-
ing its settings and release conditions is restarted after unsuccessful automatic reclosing. If the blocking time
is activated, the single-pole permission at address 3435 and the protection releases are disabled while the
blocking time expires.
Under address 3436 ADT CB? CLOSE it can be determined whether circuit breaker ready is interrogated
before reclosure after an adaptive dead time. With the setting YES, the dead time may be extended if the circuit
breaker is not ready for a CLOSE–OPEN–cycle when the dead time expires. The maximum extension that is
possible is the circuit breaker monitoring time; this was set for all reclosure cycles under address 3409 (see
above). Details about the circuit breaker monitoring can be found in the function description, Section 2.2, at
margin heading „Interrogation of the Circuit Breaker Ready State".
If there is a danger of stability problems in the network during a three-pole reclosure cycle, set address 3437
ADT SynRequest to YES. In this case a check is made before reclosure following a three-pole trip whether
the voltages of feeder and busbar are sufficiently synchronous. This is only done on condition that either the
internal synchronism and voltage check functions are available, or that an external device is available for syn-
chronism and voltage check. If only single-pole reclose cycles are executed or if no stability problems are ex-
58
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009