Abstract
This paper analyzes the lightning protection of a 110 kV underground cable line connecting two overhead transmission lines with a 110 kV substation. The transition from two overhead lines to two underground cable lines is implemented at a special double-circuit overhead line tower located approximately 2.4 km from the 110 kV substation. Lightning transients are calculated at: (i) both cable terminations, first at the transition tower and second at the substation, (ii) at the first (more critical) cable joint, (iii) at the cable sheath to the surrounding soil and objects. The latter analysis is performed to assess the risk of outer cable insulation breakdown between the sheath and the transition tower or its grounding system, as well as between the cable sheath and the substation grounding system at the opposite end of the cable. The applied surge arrester configuration is presented, and it can provide a high level of lightning protection for the analyzed system. In addition, the energy stress of the surge arresters is calculated to verify that they are not overstressed during the mitigation of lightning transients.