Investigation of High-Tension Cable Joints

With suitable cable, the successful operation of a high-tension cable system depends on the joints between consecutive lengths and this phase of high-voltage cable installation must receive considerable attention in the near future. The essential properties of a good cable joint are: 1. Simplicity of design 2. High dielectric strength 3. Low dielectric loss The dielectric strength of a joint, assuming proper care and method in assembly, depends upon the materials used. It does not necessarily follow that a joint with high dielectric strength will have low dielectric loss. Low dielectric loss is essential because of the high thermal resistance of the joint. Data is given from experimental tests carried out on seven different types of joints, four with 25,000-volt cable, and three with 33,000-volt cable. The joints were made up in the center of a ten foot piece of cable and dielectric loss tests made at various temperatures and voltages. Knowing the loss of the cable itself it was possible to determine the actual loss in the joint. In no case was this loss found to be lower than the loss of an equal length of cable. The sample of cable with the joint in the center was then tested with high potential at room temperature.