Understanding Isolation and Reconfiguration with Dead Time
Standard LA with ACR’s uses the loss of voltage at the switchgear to trigger the specific actions taken by each device. A specific time delay (LA Activation Delay) for each device is set to help ensure that the actions taken by LA to reconfigure the network occur in the correct sequence.
For example if the power is lost at one of the substations, the Feeder device opens first, then the Mid-Point device changes direction for protection and finally the Tie device closes to restore supply. LA with dead time identifies a specific dead time and uses it to trigger the same LA reconfigurations as in the standard scheme but this can be used to reduce the possibility that the Tie ACR/AS will close onto a fault.
Figure 248
Example Scenario with a potential
Tie close onto fault
The following table describes a few different reclose possibilities that could be detected by the Tie sectionaliser. In this example the Tie sectionaliser is configured with an Allow Dead Time = 25 s ± 3 s.
Table 90 Tie ACR/AS Voltage Profiles
|
Voltage profile at Tie ACR/AS |
Action |
Comment |
|---|---|---|
|
|
Allow |
Only one reclose interval equals the Allow Dead Time |
|
|
Allow |
Second (last) reclose interval equals the Allow Dead Time |
|
|
Allow |
Third (last) reclose interval equals the Allow Dead Time |
|
|
Ignore |
Power is restored on the final reclose attempt Power restored by any auto reclose action will cause LA to take no action. LA will reset if the power remains on for the duration of the LA time. |
|
|
Ignore |
Third (last) reclose interval does not equal the Allow Dead Time |
|
|
Ignore |
Second (last) reclose interval does not equal the Allow Dead Time |
