XLPE (cross-linked polyethene) medium voltage (MV) cables have proven to offer superior electrical performance, allowing for improved power loading compared to MV paper-insulated lead cables (PILC). However, PILCs are still very common in many coastal areas and wetlands in South Africa. By: Donemore Torerwa, GM: Product Development and Applications, Aberdare Cables.
The PILC product has been preferred for years due to its special features of lead sheathing, which allows for improved radial water blocking protection against moisture and water ingress, thereby significantly extending the life of a cable. Some cables have been in use for over 40 years in these networks.
Though PILC cables have proven to be resilient, there are many challenges to their continued use. PILCs are made using paper impregnated with oil as their insulation, and lead extrusion under sheathing. PILCs may pose negative environmental issues related to oil contamination when there is a cable fault at high temperatures or during cable disposal when burning. The lead or lead alloy in the PILC must be disposed of in controlled environments, which may pose challenges to many users of this product. Many countries across the world have discontinued the production of PILCs due to their negative environmental impact, and South Africa is still one of the few countries, if not the only one in the world, that is still manufacturing PILC cables for new installations because of its demand in the coastal and wetlands, and in a few mining applications.
Aberdare Cables, through its research and development initiatives, has developed an innovative solution that improves the mechanical performance of the XLPE cables to allow for their use in the coastal areas and wetlands in South Africa. This has been successful through engagements of the users of the PILCs to understand their justification for the reluctance to move to the MV XLPE cables, which have already proved to have better electrical performance in terms of current rating for the same cable size.
This new innovative solution of MV XLPE cables, now produced locally by Aberdare Cables at its Stanford Road factory in Gqeberha (formerly Port Elizabeth), consists of a radial water blocking feature making use of aluminium laminate technology, addressing the drawbacks to change from PILC to more environmentally friendly MV XLPE cables and allowing for improved life in MV XLPE cables. This product is available throughout Africa and globally as well.
The new solutions are already covered in the local standards SANS 1339 of 2020. SANS 1339 is a compulsory standard in South Africa covering cables with voltages rated from 6.6 kV–33 kV (MV cables). This standard specifies longitudinal and radial water blocking for MV cables when required by the user of the cable. Longitudinal water blocking is the most commonly deployed water blocking method as applied by many cable manufacturers in the local market, mainly because it is relatively easy to implement. Longitudinal water blocking alone, however, may not be enough to offer lasting water blocking capabilities of a cable in some environments, especially in areas that have high water levels in the ground. Offering radial water blocking becomes key for cables to ensure enhanced water blocking capability of MV XLPE cables at the design and manufacturing level.
Radial water blocked cables are not very common in South Africa for MV cables. They are common for high voltage (HV) cables for 44 kV–132 kV-rated cables, making use of Corrugated Seamless Aluminium (CSA).
