ACO using Classic LA

Overview

Classic LA can help ensure that supply is provided to a vital load (for example, a hospital) by implementing an ACO scheme with Make before Break restoration that does not rely on communications between devices. This scheme helps to ensure that the vital load maintains supply providing either the normal or alternate supply is available.

ACO Configuration

The scheme must be set up as shown in the figure below.

The ACR on the normal or preferred supply must be configured as a Feeder type and the ACR on the alternate supply must be configured as a Tie.

The Tie ACR must be configured to Tie Restore One Way. This helps to ensure that the Tie ACR does not close to back-feed the alternate supply if it is not available.

ACO Operation

• If the normal supply is lost, the Feeder ACR will detect loss of supply on its source side and trip according to RULE A. The critical load will experience a temporary loss of supply.

• The Tie ACR will now detect a loss of supply on its load side and close according to RULE C. This restores the supply to the critical load from the alternate supply.

ACO Restoration

Make before Break restoration can be achieved using Classic LA functionality.

• If the normal supply returns, supply will be restored to the sources side of the Feeder ACR and it will close according to RULE F.

• Once the normal supply takes up its share of the load, the Tie ACR will trip according to RULE E.

WARNING
HAZARD OF UNEXPECTED EQUIPMENT OPERATION Generator must not connect to a grid with a large phase angle differences. Person must stay away from the generator. Failure to follow these instructions can result in death, serious injury, or equipment damage.

Pros and Cons of using LA for ACO

There are some points to be considered when using LA in an ACO scheme:

• Advantage: No communications between ACR’s is required.

• Disadvantage: Only Make before Break restoration is available.