Feasibility of reduced insulation thickness in medium voltage power cable designs

Rural and suburban areas in Finland mainly implement overhead lines for distribution at the 20 kV level. Large scale outages resulting from severe storms have added pressure to develop weather-proof distribution networks. Replacement of existing overhead line systems with traditional cables and traditional installation techniques is far too expensive an operation to undertake. As such, the development of novel cable installation methods are required along with new types of cables. A new cable design with reduced insulation intended for both underground and overhead installation was investigated as part of a sustainable community research program. Although the thickness of the new cable insulation differs from IEC standard nominal values, the new cable design successfully passed large scale electrical testing according to international and national standards. Cable accessories including terminations for indoor and outdoor installations and cable joints also passed the testing routines. From the tests it was concluded that the quality of the installation work is crucial - the observed issues are not related to the insulation system but to the quality of installation and assembly. Thus, this crucial point requires particular attention in real installations.