Performance of outdoor insulators in tropical conditions of Sri Lanka

Ceramic insulators, specifically porcelain and glass insulators, have widely been used all over the world since the 19th century [1,2]. However, when such insulators are energized and exposed to different pollution environments under different climatic and weather conditions, leakage current (LC) develops along their surfaces [3-7] and eventually cause flashovers. Various remedial measures have been adopted by power utilities to mitigate this problem. Among the common methods are: (a) increasing insulator creepage (leakage) distance, (b) reducing supply voltage, (c) insulator washing (cleaning), (d) oiling or greasing (silicone) the insulator surface, and (e) insulator replacement. Composite insulators, also referred to as non-ceramic or polymeric insulators, have also been used during the last six decades as an alternative to the ceramic insulators [8-10]. The housing materials most often used have been silicone rubber (SIR) [11] and ethylene-propylene-diene-monomer based rubber (EPDM) [12]. Water repellent (hydrophobic) properties of composite insulators, light weight, resistance to vandalism are among the main reasons for their usage. This has been proven by positive outcomes of numerous studies performed in laboratory and field conditions [8,9,13-16]. However, due to exposure to harsh service stresses such as corona discharges, UV radiation and chemical attacks etc., the housing materials may lose hydrophobic properties and develop surface degradation (tracking, erosion). In addition to the ever-increasing use of composite insulators, polymeric coatings (mainly RTV silicone rubber) [17] and semi-conducting glazes [18] have also been adopted for improving performance of ceramic and glass insulators [19].