Why are stress cones used in cable termination?
When a high-voltage cable is cut for termination, the metallic sheath or screen of the cable is also cut. As a result, a sharp edge is created at the cut end of the sheath. At this sharp edge, the electric field becomes highly concentrated, which produces high voltage stress at that point. This excessive stress can weaken the insulation and may lead to insulation breakdown.
To reduce this problem, a stress cone is installed at that location. A stress cone is usually made of graded insulating and semiconducting materials, and it works similarly to a graded capacitor. The stress cone distributes the electric field uniformly and reduces field concentration at the cut end. Therefore, the voltage stress at the cable termination point decreases, and the chance of insulation failure is reduced.