An Automatic-Changeover (ACO) scheme enables supply from either of two sources in support of a single load. These types of schemes are normally used in support of a critical load such as a hospital to ensure that alternate supply is always available in the event of power failure. Such a scheme requires switchgear with proven reliability and a degree of automation which removes any necessity for the operator to become involved in the switching process.
The built-in voltage sensors of our range of reclosers and sectionalisers mean that a cost effective source-changeover scheme can be implemented for loads where security of supply is vital.
A recloser is used in the feeder connecting the preferred supply to the load. This recloser is configured as the Master Device, and is Normally Closed. The alternate supply is connected to the load via a Normally Open recloser which is the slave device.
The master and slave devices communicate via an ACO communications link. This allows the master to monitor the supply availability and to send commands to the slave device. Status information can be transmitted via DNP3 communications to the control centre if required.
When the preferred supply is lost due to an upstream fault condition, the controller at the closed Master Device automatically trips the recloser and then instructs the Slave Device to close. This sequence automatically connects the load to the alternative supply.
When the Master Device controller detects that the fault condition has been cleared and the preferred supply source has been restored, it automatically restores supply back to the normal configuration.
The changeover of supply will not commence if supply has been lost downstream of the recloser due to a fault condition resulting in it tripping to lockout. In this situation the Slave Device would remain open.
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