Siemens 7SR224 Technical Manual page 337

7SR224 Argus Applications
As can be seen from the above, the NOP and each Recloser will close sequentially at the User set (e.g. 5
seconds) intervals and each Recloser when it Closes will be primed to perform a single Fast Protection Line
Check Trip & Lockout for its Close whilst all other Reclosers/NOP have had their protection changed from Fast
Protection Line Check Trip & Lockout to a Delayed Line Check Trip & Lockout; this ensures that the Recloser
closing onto a faulted section will trip Fast Protection and clear the fault leaving all the other proven, unfaulted,
sections energised. This mode of operation does impose a fault, which will be cleared by a single high-speed
Fast-Protection Trip, onto an otherwise healthy system but it does result in 'as much of the System being
maintained in-service as possible'.
If, following a Loss of Voltage and LOV Automation initiation, a type Recloser does not see Voltage re-appear on
one side to allow the LOV Automation process to proceed, then on expiry of the LOV Sequence Time i.e. the LOV
Automation time-allowed-to-live timer, the LOV Sequence will be terminated and the Recloser will go to Lockout.
The NOP and the Reclosers involved in the restoration sequence must have their LOV Reclaim Time settings set
to a longer time, with grading margin > 5 secs, than the maximum time taken for the last Recloser X in the LOV
Sequence to complete its LOV sequence and Reclose, tripping to clear any permanent fault which presents itself
as necessary. This is necessary to ensure that the NOP and all Reclosers, which will see fault current when the
last Recloser in the sequence closes, remain programmed to perform a Delayed Trip without reclose until after all
Reclosers have completed their part in the Automation sequence and the system is restored unfaulted.
Once the NOP and feeder Reclosers have completed their LOV sequences and have LOV Reclaimed then they
must now have co-ordinated grading to be able to deal correctly with a second fault on one of the healthy
sections. This co-ordinated grading, under back-feed conditions following NOP(TIE) closure, is achieved by
programming all the Reclosers in the LOV back-feed loops to be bi-directional, their settings in both directions can
be co-ordinated by a Grading Study to ensure correct grading for faults fed from either the normal Forward or
NOP(TIE) Closed back-feed, Reverse directions.
LOV Element has two main outputs i.e. three pole LOV Trip and three pole LOV Close these can be mapped to
the existing CB Open and 79 AR Close outputs, it is not necessary to create new outputs in the output matrix, all
other outputs are intended for alarm/indication purposes.
It should be noted that in a typical interconnected system at each feeder end there could be up to 3 NOP (TIE) at
that node anyone of which could be closed to back feed supply to that feeder, therefore, there must be a user-set
pecking order. The NOP LOV Action Delay timer User settings with grading margins e.g. 75 s - 80 s - 85 s,
ensures that the optimum reconfiguration of the system occurs but with redundancy built-in to ensure that supply
is restored via a third path should the first or second, choice path not be available or fails, see Error! Reference
source not found. .
Loss of Voltage at the NOP on V /V /V selects the LOVa Action Delay timer setting; Loss of voltage on V /V /V
A B C X Y Z
selects the LOVx Action Delay timer setting. As can be seen the result is that each Feeder can have a preferential
first choice, a second choice and third choice back-feed feeder, the user can set these independently to suit his
system. NOP (TIE) to Feeders from other Sub/Stations will typically always be set to third choice e.g. 85 second
Action Delay time. NB the NOP LOV Automation Action Delay on either side can be set to OFF which means that
the User can select NOP LOV Close so as to supply power in a single first required direction only, not a second.
The bubbles show examples of the flexibility of the grading arrangement at the node on the end of each feeder,
st nd rd
showing how the user can select the 1 , 2 and 3 choice back-feed feeders for each feeder. Other
arrangements can be set-up by User. Note the NOP (TIE) feeders between Sub/Stations end up with the same
Action Delay time settings on both sides.
The LOV Automation function can be Enabled or Disabled, by the User setting and can be switched In/Out
dynamically via any Binary Inputs, LOV can also be switched In/Out by Function Key or SCADA General
Commands. LOV is automatically inhibited by Voltage Transformer Supervision if a VTS failure is detected.
For a controller with LOV Plant Device Type set as Recloser to perform its LOV Automation sequence, only the
downstream voltage needs to be monitored and therefore addition primary voltage transformers are not required.
Reclosers should be mounted and connected so that the standard Voltage measuring devices are on the
downstream side as this voltage is monitored for voltage recovery to prompt reclosure. The controller monitors will
respond to voltage restoration on either side of the recloser and therefore connections can be made to the 'A' or
'X' side.
For a NOP (TIE) to perform its LOV Automation sequence, the voltage levels on both sides of the NOP i.e. both
downstream and upstream voltages, must be monitored. Voltage levels must be continuously monitored as pre-
LOV memory of condition states is necessary.
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