Siemens 7SR224 Technical Manual page 336

7SR224 Argus Applications
NOP (Tie): This device operates as a normally open point in the network which is closed automatically as part of
the sequence to provide a backfeed from a different, unfaulted feeder when voltage is detected as lost.
Feeder: The controller issues a trip on detection of LOV, followed by no further action to establish a new normally
open point in the network arrangement which results from the automated sequence.
The starting point is that on a normal healthy system all Reclosers A, B & C on both Feeders will be closed as
shown in
and the NOP will be open. All Devices will have the same voltage on their upstream and downstream sides and
voltage will be present on both sides of the NOP (TIE) point. It should be noted that Reclosers at different points
in the system are programmed to give the optimum, different, reaction to Loss Of Voltage and that their response
is not conditional on seeing fault current, only on detection of loss of voltage. An LOV sequence starts to operate
due to prolonged absence of voltage which occurs when a CB or Recloser goes to Lockout after a persistent fault
is isolated from the supply i.e. fault current no longer flows, following a complete but unsuccessful autoreclose
sequence. The actual cause of the fault still remains but is isolated on its normal source side from the supply and
from adjacent feeders by the NOP.
For a fault at the position shown on the Feeder 1- A section, the 1A CB/Source Recloser will go through a
sequence of Fast plus Delayed trips to attempt to clear the fault. For a permanent fault the outcome will be that
1A goes to Lockout and Feeder 1 will be left totally dead. Feeder 1 does however have healthy sections e.g. 1B to
1C and 1C to the NOP which can be given back-feed supply from Feeder 2 if a structured restoration cycle is
initiated by the automatic closure of the NOP. This is achieved as follows;- following the Lockout of the Source
Recloser/CB-1A, the Line Reclosers 1B and 1C will both see permanent Loss Of voltage (LOV), (this may also
have occurred temporarily, more than once during or for the whole, of the 1A recloser sequence).
1B and 1C can be set as type Recloser in the LOV Automation menu. In this case if LOV Recloser Opening in
each is set to Enabled and they see permanent LOV on both sides for more than a user set LOV Action Delay
e.g. 60 seconds, set by the user to cover a complete upstream sequence, then their LOV Elements will each take
action and give a 3 pole Trip output, both 1B and 1C will therefore Trip and Lockout at about the same time.
The NOP, which is set as type NOP (Tie) in the LOV Automation menu, in example 1, will see LOV on its Feeder
1 side and will have normal system voltage available on its Feeder 2 side; if the NOP's LOV Element sees
permanent LOV on either side i.e. lasting for more than a user set LOV Action Delay e.g. 75 seconds to give a
grading margin to allow time for Reclosers 1A and 1B to open at, for example, 60 seconds, then the NOP LOV
Element will take action and issue a NOP Close.
A type NOP (Tie) has separate settings for LOV-A Action Delay and LOV-X Action Delay to allow different delays
to be applied for Loss of voltage action on either side of the Recloser.
For this NOP Close action the NOP Protection must be primed to perform one Fast Protection Line Check Trip &
Lockout, thus, if the NOP closes onto a permanent fault or a fault appears during a set LOV SOTF Time (e.g. 5
seconds), on section 1C then the NOP will perform a Fast Protection Trip & Lockout. If the NOP close is
successful and no fault appears, the C section of Feeder 1 will thus be back-fed. The NOP Line Check mode
must be maintained as Fast Protection during its LOV SOTF Time but must then be changed to Delayed for the
Recloser's LOV Reclaim Time .
Recloser 1C will now see voltage on its downstream side and if that voltage is present for the user set LOV SOTF
Time e.g. 5 seconds, then 1C's LOV Element in turn will then issue a Reclose and 1C will close. Note that the 1C
Protection will be primed to perform one Fast Protection Line Check Trip & Lockout, thus, if 1C closes onto a
permanent fault, or a fault appears during its set LOV SOTF Time e.g. 5 seconds, then 1C will Fast Protection
Trip and Lockout. If the Recloser close is successful the B section of Feeder 1 will thus be back-fed. The 1C Line
Check mode must be maintained as Fast Protection during its LOV SOTF Time but must then be changed to
Delayed for the Recloser's LOV Reclaim Time .
Recloser 1B will now see voltage on its downstream side and if that voltage is present for the user set LOV SOTF
Time e.g. 5 seconds, then 1B's LOV Element in turn will then issue a Reclose and 1B will close. Note the 1B
Protection will be primed to perform one Fast Protection Line Check Trip & Lockout thus if 1B closes onto a
permanent fault, or a fault appears during its set LOV SOTF Time e.g. 5 seconds, then 1B will Fast Protection
Trip & Lockout. If the Recloser close is successful then the A section of Feeder 1 will thus be back-fed. The 1B
Line Check mode must be maintained as Fast Protection during its LOV Reclose reclaim Delay but must then be
changed to Delayed for the Recloser's LOV Reclaim Time .
For the example shown 1B will be reclosed onto a permanent fault and will therefore perform its Fast Line Check
Trip & Lockout with 1C now applying only Delayed protection. This will leave the healthy 1B and 1C sections
backfed via the NOP.
©2010 Siemens Protection Devices Limited Chapter 7 Page 37 of 50