An investigation into the feasibility of migrating from PILC to XLPE as the cable technology of choice for medium voltage electricitiy networks in South Africa.

Abstract

South African medium voltage underground electrical networks consist mainly of cables of paper insulated lead covered construction. This construction is still the standard used for most utilities in South Africa. While the in-service performance history of these cables has been excellent, global manufacture of this cable type is decreasing. Internationally, the use of polymeric cables is increasing, resulting in the security of the supply chain for paper cable becoming an increasingly important issue. The most widely used polymeric construction is cross-linked polyethylene. Modern distribution switchgear, which is increasingly used in South Africa, is designed for the newer polymeric technology as this enables more compact construction and reduced equipment footprint. The reduced clearances present installation and operational issues when using modern switchgear with paper insulated cables. Although a comprehensive literature review was conducted, not much academic work has been done on the process of migrating from one cable platform to another. Manufacturer data, academic reference sources, industry experts and software modelling tools are used to demonstrate that the use of polymeric technology is viable for South African utilities. This dissertation focuses on the difference between paper and polymeric technologies, and explores the advantages and disadvantages of each. Integration issues are examined along with the methods used to overcome the challenges of hybrid or mixed dielectric networks. Economic comparisons between paper and polymeric cables with respect to purchase and operating costs (including the cost of losses) as well as steady state, cyclic, distribution and emergency current ratings are made. The dissertation concludes that it makes economic and engineering sense for users of paper cable in South Africa to change to polymeric technology, taking the recommendations given into consideration in order to choose an optimised cable design and gain maximum benefit from the change.