Sub transmission insulator and conductor ageing in coastal environments.

Abstract

Globally, power grids are gradually unbundling to encourage multiple sources of small to medium scale renewable generation, aiding in relieving demanding power constraints [1]. The additional generation product requires an effective and efficient power evacuation system; however, the constrained transmission and sub transmission systems are burdened with the higher power transfer limits coupled with aged infrastructure. Operations and maintenance strategies assist in alleviating the temporary system load increases; however, an asset management strategy is required to ensure that the power system operates at a peak without encouraging a redesign or replacement of the entire power system [2]. The guiding principles of an asset management strategy is understanding the effective utilization of sub systems and components. Effective utilization of components can only be achieved, once a useful lifespan is determined, replacing, refurbishing, or instituting life extension measures once the component end of life is neared. To avert underutilizing or overutilizing the asset, the asset age base needs to be determined incorporating in-situ conditions to provide a reliable and generic prediction model. In sub transmission and transmission systems, maintenance funding, is allocated to critical components such as insulators, ACSR phase conductor and galvanized steel shield wire. These high failure-impact components are susceptible to a higher rate of corrosion related failure, attributed to environmental conditions such as high humidity and high air contamination found in coastal environments. The corrosion models guided by ISO 9223 [3], makes use of empirical degeneration rates for Aluminium, Steel and Zinc. These models understate the initiation of the corrosion reaction for the first year only, requiring the derivation of an acceleration model to represent the degeneration of the composite conductor over its lifespan. The resulting model predicts the useful life of the conductor by measuring the loss in tensile strength attributed to corrosion. Age prediction modelling of the silicone composite insulator is achieved by predicting the loss of creepage or resistive layer on the insulator surface. The coastal environmental conditions, contribute significantly to degenerating the resistive layer leading to a flashover at line voltage. The validation of the insulator and conductor ageing models are achieved by comparing the calculated lifespans to measured field-samples tests. The results showed a standard deviation of 4 years between the measured and calculated values.