A New High-Interrupting-Capacity Fuse for Voltages Through 138 Kv

The reliable performance of high-interrupting-capacity fuses in the intermediate voltage field has led to an increased interest in the application of such fuses for the higher voltages. Unfortunately, a fuse for the higher voltages cannot be made by simply enlarging or lenghthening the lower-voltage devices. To interrupt the higher currents in a reasonable structure, arc lengths must be kept short to reduce mechanical stresses. Interruption in these short distances creates high dielectric stresses external to the fuse that would endanger the operation of a device built along conventional lines. Adequate conductors for carrying the higher currents through the longer-length fuse must be moved quickly during interruption. A new high-voltage fuse in which interruption of the higher currents is acomplished in a short length without undue voltage stresses adjacent to the fuse has been developed. This fuse has a new arrangement of conductors which permits rapid extension of the arc without expulsion of any conductor parts from the fuse. All this has been accomplished with a fuse of such light weight that it permits the use of a drop-out design which is a necessity at the higher voltages to prevent subsequent flashovers caused by leakage currents. The interrupting medium is compressed boric acid which has proved very effective and reliable at the lower voltages. Repeated interrupting and mechanical tests have demonstrated the suitability of the new fuse for service on important transmission circuits.