Uprating of 275kV Lines to 400kV as Part of a Contingency Plan for Generation Integration

Multiple generator transformer failures at the Eskom Lethabo power station caused the situation whereby the only available spare transformers had a secondary voltage of 400 kV. The only practical solution was to upgrade the existing 275 kV integration to the national grid to 400 kV, within a time constraint of three months. The 275 kV Lethabo-Glockner 1 and 2 lines were earmarked for the uprating. These lines were audited to validate line components and provide the background to investigate solutions. Practical configuration changes were effected mainly through the innovative modification of the phase assembly insulation, substantiated by theoretical studies and full scale electrical and mechanical tests where possible. The uprated lines have been operating successfully at 400 kV at the time of writing. This project has serious ramifications for other uprating lines projects. This paper focuses on the technical challenges experienced and the unique design solutions proposed and implemented by the line designers