Method and apparatus for operating cabled-fiber undersea network, and fault-tolerant branching unit for use therein

Abstract

A powering arrangement for an undersea cable system provides that each branch of the system is supplied with a current equal to half of the current in the trunk. By coupling both branches to the trunk, the current adds at the branching unit. Upon occurrence of a power path fault in any branch, a virtual ground moves to the site of the fault. In addition, an image virtual ground moves to a similar point in the branch that does not have the cable fault. As a result of this implementation, the cable power system is able to tolerate at least one fault in a branch without necessitating repair, and can tolerate some multiple branch faults depending upon their location. In contrast to the operation of existing power-switched branching units, the fault-tolerant branching unit does not require down-powering and re-powering in order in order to change the power configuration, e.g., to allow a virtual ground to be re-located at shunt fault sites that occur in either trunk or branches. Moreover, even with a branch shunt fault or cable break, the fault-tolerant branching unit allows for power to be removed from the faulted branch for repair without having to first power down the other two legs. And finally, at the completion of a branch repair, power to the repaired branch can be restored without first powering down the other two legs.