Close On Zero; Loss Of Voltage (Lov) Loop Automation Function - Siemens 7SR224 Technical Manual

24 / (1.6 x 180) = 83mHz. If the relay were to close on the boundary the phase angle traversed in the 160ms total
delay time is given by,
( ) (
θ
Δ = × ×
Slip 360 t
CB
Therefore the CB will close at 24° + 4.80° = 28.80°.

4.2.10 Close on Zero

Close on zero is the preferred method of some customers for restoration of a split system. The relay
uses the measured slip frequency and the typical closing time of the circuit breaker to issue a close
pulse, as the phase difference is reducing, which will close the circuit breaker when the phase
difference is zero. High accuracy is not required regarding the CB Close Time.
4.3

Loss of Voltage (LOV) Loop Automation Function

This additional functionality is available as an ordering option when required to suit application requirements. The
LOV Automation function is applied by Reclosers at the sectioning points along a feeder and by a Normally Open
Point (NOP) at the junction of two feeders, see
, the purpose is to ensure the automatic restoration of system supply to as many customers as is possible
following the lockout of a source Recloser and de-energisation of a feeder due to a permanent fault. The resultant
permanent loss of supply to healthy sections of the faulted feeder can be avoided by the sequential closure of the
NOP (TIE) Recloser and multiple Line Reclosers to back feed supply and isolate the faulted section. This
sequence can be triggered by Loss Of Voltage to automatically and relatively quickly, restore the power to healthy
sections and thus limit the disruption to Customers and minimising the Customer Minutes Lost (CML) metric. LOV
Automation should be considered as a one shot automated sequence after which, the normal NOP having been
closed, manual operations should be taken to clear the fault and restore the system to its normal configuration.
The LOV Function described does however have the capability of reconfiguration after other permanent fault(s)
occurring, after the first-fault LOV automation sequence, depending on their location within the system. However,
if no manual action is to be taken the increase of load level on the back-feed feeder(s) must be considered.
Feeder 1
1A
Feeder 2
2A
Figure 4.3-1 Sysyem Diagram showing Normally Open (TIE) Point
Reclosers in the network must be designated as one of 3 different types:
Recloser: If a LOV condition is diagnosed when the recloser is in the closed state, the controller issues a trip then
subsequently recloses on restoration of voltage as part of an automated sequence to provide sectioning points
along the feeder.
©2010 Siemens Protection Devices Limited
)
+
t
RELAY
= 0.083 x 360 x 0.16 = 4.80°.
A B
1B
Vabc Vabc
2B
Vabc Vabc
7SR224 Argus Applications
C
1C
Vabc
'Vabc'
NOP
(TIE)
'Vxyz'
2C
Vabc
Chapter 7 Page 36 of 50