Reviewing of Insulator Selection Criteria for Overhead Power Lines in Coastal Areas of Sri Lanka

At present porcelain and glass insulators are used for overhead power lines in Sri Lanka. Salt contamination on insulators of coastal lines assists leakage currents to passing over the insulator surface and cause insulator flashing over. Frequent power outages due to flashing over of insulators on overhead power lines are common in coastal areas and it reduces the reliability of the power system considerably. It has been observed that this problem is very severe in costal lines in dry zone of Sri Lanka especially in Puttalam, Mannar and Jaffna areas. Partial blackout caused by flashing over of insulators on 220kV transmission line running closer to the sea and across the Kalpitiya lagoon from Norochcholai coal plant to Veyangoda switching station shows the severity of this problem. Therefore it is timely requirement to review the insulator selection criteria for overhead power lines to find out mitigation measures against the flashing over of insulators due to marine pollution. This paper describes the mechanism of flashing over of insulators due to marine pollution and highlights the limitations of the presently following electrical standards for insulator selection based on field measurements and maintenance experience. It is emphasized that the most successful method that can be employed to determine the ideal insulator out of insulators made of different materials and of different shapes is to verify their performance by conducting long term field measurements at the exact environment. Apart from that the existing practices applied on distribution network to minimize insulator flashing over is evaluated technically and financially in order to identify the best solution. Application of new technology such as adaptation of polymeric insulators, insulator coating materials and applicable online insulator washing techniques are also investigated. The importance of type test reports named as artificial pollution tests to understand the pollution immunity of insulators is also discussed. The value of establishing insulator field testing stations in problematic areas is strongly recommended and the test techniques applicable in field evaluation of insulator performance are briefly explained.