Cable automation for urban distribution systems

Located underground, cable distribution systems have a long track record of being very reliable. However, when faults do occur, the customer minutes lost (CML) is often much greater than for faults on the rural system. With more traffic congestion predicted for major cities, getting people to substations quickly will be a bigger problem; therefore, longer delays in restoring supplies are to be expected. Today's requirement is to automatically locate cable faults and to communicate the response to central control. Supplies can then be restored quickly, and crews directed to make the repair. The paper describes the novel 'Cable @utomat' approach. Using a series of earth fault sensing transmitters located at convenient points along the cable feeder, and a receiver at the primary substation, the transmitters communicate with the receiver using the primary cable as the medium. To improve overall system reliability, transmitters are uniquely coded so that the receiver can identify each one. This offers a major safeguard against incorrect fault location. Maintenance of fault location equipment represents a large cost to users. By adding regular healthy reporting, the maintenance strategy can be made pro-active; demanding no action until a failure is reported. Finally, the paper describes short-lived pecking faults, often found on cables, that can easily confuse fault location methods. The new product has added design features to ensure reliable operation under such difficult conditions.