Intelligent LA Operation

Intelligent LA Enhancements

The Intelligent LA feature has been enhanced to allow users helps to prevent a feeder device from tripping or a mid-point device from selecting its alternate protection group, after its LA Timer has expired following a loss of supply, if the supply has been lost to both sides of the corresponding Tie device in the network. This setting may be useful where the Tie device is supplied from a common source.

Figure 243
Intelligent LA configuration for suspend when Tie loses both supplies

The Suspend When Tie Looses Both Supplies setting can only be enabled if Tie control is selected as Message. To help prevent a feeder device tripping or a mid-point from selecting its alternate group when supply has been lost on both sides of the Tie, the Suspend When Tie Loses Both Supplies setting must be configured at the Tie and all other devices in the scheme. This is verified as part of the iLA scheme validation tool. If enabled, and if the Tie loses supply to both sides, the Tie will send a Suspend message to all upstream devices in the scheme.

Range: On/Off

Default: Off

The Feeder and Midpoint devices suspend operation when this setting is enabled after they lose supply and receive a Suspend message from the Tie.

If the supplies are restored to both sides, the LA goes back to normal on all devices.

If the supply is restored to one side only of the Tie, a message is sent by the Tie to the upstream devices (Feeder and Midpoints) on the side where supplies remain off, confirming supply can be restored from the Tie. On receipt of this message the feeder which has lost supply will trip open, Midpoint devices which have lost supply will change protection group and send a close request to the Tie. The Tie will close to restore the supply to that section of network. If there is loss of communication either when the iLA timers are timing or after receipt of the Suspend Loop Auto message from Tie, the scheme defaults to the original behavior. That would mean that in case of loss of communication when Feeder detects a loss of communications while suspended, it would then trip and turn LA OFF, and similarly a Midpoint will select its alternate protection group and disable iLA.

Firmware (A50-15.04) and above must be used on all the devices in the scheme.
The PING interval must be less than the Activation Delay.

Intelligent Re-Configuration Rules

Intelligent LA can operate in a more informed fashion than Classic due to communications between devices.

It complements the basic Classic LA operation rules with the following rules for Intelligent LA.

When either a Feeder or Mid-Point device goes to lockout due to a protection operation, it sends a trip request to its downstream device if that device is a Mid-Point.

A Feeder device also sends a trip request to its downstream device if that device is a Mid-Point when it trips to lockout after losing its source supply (Classic LA Rule A).

If the device downstream from the locked out Feeder or Mid-Point is a Tie, the locked out device sends a close inhibit request message to the Tie. This helps to prevent it from closing onto a detected fault.

If Tie control mode is Message, and the device downstream from the locked out device is a Mid-Point, the locked out device also sends a close request to the Tie in the scheme. A close request is sent upon confirmation of the successful operation of its downstream Mid-Point device. If this confirmation is not received, the locked out device does not send a close request to the Tie.

If Tie control mode is Timer, a Tie operates as per its basic Classic LA Rule C, regardless of receiving a close request or not. This mode maintains the availability of the scheme and enables an automatic attempt to restore supply regardless of the availability of the peer-to-peer communications.

If Tie control mode is Message, a Tie operates only if it receives a LA close request.

NOTE: The rules above are a simplification. For all the rules in detail, refer to Appendix L.1 Loop Automation Operating Rules. For more information on LA with AS rules, refer to Appendix L.3 Network Configuration Example.

Timer Tie Control

The Timer Tie Control option is based on a single message sent by a Feeder or Mid-Point device which goes to lockout on a protection trip.

The message is received either by a downstream Mid-Point or Tie.

When a downstream Mid-Point receives the message, it trips once to lockout to isolate an upstream detected fault.

When a Tie receives the message, it turns LA OFF helps to prevent closing onto a detected fault.

To help prevent a Tie from closing onto a detected fault, the message needs to be sent before the Tie LA timer expires.

The LA timer starts when the device has no supply available on the first trip of the protection sequence.

The window for the message to be sent is: Tie LA delay minus protection sequence time.

Typically this is in the order of 5 s.

The sending of the message can be attempted multiple times. The attempt count and time out are configurable.

Message Tie Control

In the Message Tie Control mode, the Tie switchgear device closing is controlled by a message.

When the Feeder or Mid-Point device goes to a protection lockout, it initially sends the same message to the downstream device as described above in Timer Tie Control.

The downstream device also reacts to the message as described in the Timer Tie Control. If the downstream device is not a Tie, an additional close message is sent to the Tie.

If the Tie does not receive a close message, it does not close the switchgear when it has no supply available and the Loop Automation Activation Delay expires.

If the close message is not received before the LA delay expires, it turns LA OFF.

This also means that the total message retry period must be shorter than the LA Activation Delay.