An improved optimal design scheme for high voltage cable accessories

Cable accessory always fits cable with a shrink range in order to ensure a certain interface pressure in the actual use, so cable accessory keeps in the expansive state after installation. But the expanded accessory will lead to not only a thinner insulation thickness and a shorter length but also a possible problem in the accessory, as the angle of stress cone and the shape at end of high voltage (HV) shielding tube may far deviate from the original design structure. This will be a vital threat to the reliability of cable accessory in service. In this paper, an improved design scheme for HV cable accessories was proposed to ensure the optimum electrical design after installation. The key process was the deduction of deformation and displacement equations of cable accessory during expansion by the theory of elastic mechanics. As joints are always much weaker than terminations in the cable system, the case studies were conducted only on cable joints in this paper, and the electrical fields were calculated to evaluate their performances. By contrast with the electrical field distributions before and after improvements, the results show that the expansion will not only change the joint structure but also aggravate the electrical fields at the interface or in the bulk of the joint. At last, a comparison was made on an actual cable joint which kept in the expansive or relaxation state, so as to verify the correction of the deformation and recovery equations proposed in this paper. This improved design scheme can also be applied for termination design, especially be great helpful for the higher or extra HV cable accessories‚ manufacture and the long-term operation safety.