C I R E D 21 st International Conference on Electricity Distribution Frankfurt, 6-9 June 2011 Paper 1266 Paper No 1266 1/4 ASSESSMENT OF IN SERVICE COMPOSITE INSULATORS IN VERY HARSH COASTAL ENVIRONMENT OF IRAN: LABORATORY & FIELD TESTING Majid REZAEI Mohammd Reza SHARIATI Sasan JABBARI N.R.I – Iran N.R.I – Iran H.D.E.C - Iran marezaei@nri.ac.ir mshariati@nri.ac.ir jabbari_sasan@yahoo.com ABSTRACT Long-term assessment of composite insulators is a main target of this paper. The evaluation approach consists of both laboratory and field testing. As a first step, in laboratory testing following activities is considered: visual inspection, mechanical and electrical investigations and material analysis (core, sheds and pollution layer) and metal fitting assessment. In field inspection step long time leakage current monitoring of samples (5 years) has been selected as a main strategy. All test results showed that the different properties of samples were fairly well even though they had been energized for 10 years in heavily contaminated areas. Reasons to doing this procedure are to determine the inspection frequency and to determine whether to leave the population, or individual units, in service or remove them. Based on the test results we decide to remain these insulators in service. The life expectancy of these insulators estimated at least 20 years (till 2020 in service). The next assessment time for further and more precise analysis is also determined INTRODUCTION In recent decades, replacement of porcelain insulators with composite ones is considered as an effective approach to overcome undesirable effects of high level marine–desert pollution in southern coastal regions of Iran. The superior hydrophobicity and the withstand voltages of pollution flashover of silicone rubber insulator which are much higher than those of conventional insulators are the main reasons. However on the other hand, since composite insulators suffer from ageing due to electrical stresses such as dry band activity and environmental stresses such as UV radiation and acid rain, the utilities concern about the future condition of composite insulators in their network. These stresses may cause surface, chemical and structural changes of polymer in long time in service operation which that may reduce the desired properties of materials which during time may lead to insulation failure in system. As experiences with composite insulators are significantly less than porcelain insulators, therefore providing the useful method to evaluate the performance of composite insulators is an urgent enquiry. The feasibility study of healthy future operation of this in service insulators is also essential to improve the reliability of electric networks. CLIMATIC CHARACTERISTICS OF REGION According to DIN50019, the coastal districts of Persian Gulf are classified as extreme hygrothermal climatic zone. Unusually high saturation vapor pressure up to 53mbar observed in this zone, justify this marking, as such air humidity phenomena are unique in the free atmosphere of the earth and are absolute extremes. Intensive night falls of dew, which can occur regularly for several months, long periods of rainless and sultry weather and high level of marine pollution worsening the situation for power lines. [1] Regional pollution map The pollution map of region based on the ESDD-NSDD measurement level has shown in Figure.1. The pollution level of this region is classified at very heavy category.[2] Figure1.Pollution map of region SPECIMEN INSULATORS Ten pieces of naturally aged HTV silicone rubber Insulators are removed from the 20 kV distribution line located in coastal district of Hormozgan province of Iran as representative samples of an age generation. Since year 2000 these suspension insulators operate in this distribution network without any flashover or failure experience. Also two samples are chosen from stock as reference. (Figure.2) overall distance : 480 mm , SML = 70 kN Rod diameter: 18 mm , Creepage distance : 900 mm Figure2. Sample insulator