Evaluation of Field-ageing Effects on Insulating Materials of Composite Suspension Insulators N.C. Mavrikakis, P.N. Mikropoulos High Voltage Laboratory, School of Electrical & Computer Engineering, Faculty of Engineering, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece and K. Siderakis Electrical Engineering Department, School of Engineering, Technological Educational Institute of Crete, Heraklion 71004, Greece ABSTRACT Condition assessment of naturally aged composite insulators, aiming to better understand the ageing processes involved, is essential for maintaining high reliability in power networks. In this study field-ageing effects on insulating materials (EPDM and VMQ/HCR) of two 150 kV composite suspension insulators are evaluated. The insulators had been in service for 17 years on a coastal transmission network, exposed to seaborne salt spray, windborne soil deposits and intense UV solar radiation. Several diagnostic techniques, including visual inspection, wettability classification, FTIR spectroscopy, SEM and EDX analysis were employed to assess the condition of the insulators. Field-ageing effects were not assessed as critical to dictate insulator replacement. For both insulators morphological and material degradation due to field- ageing was restricted to the upper surface layer of the polymeric housing. The resistance of housing material against tracking and erosion remained unaffected by field-ageing. Surface deterioration of EPDM was more intense than that of VMQ/HCR, despite the fact that the EPDM insulator had been in operation at a site with a lower pollution severity. The EPDM housing was classified as hydrophilic; however, after removing pollutant deposits its hydrophobicity was improved. The hydrophobic properties of the VMQ/HCR housing were only slightly reduced. Field-ageing effects on insulator housing are discussed based on material structural changes caused by ageing stresses. Index Terms - Ageing, chalking, cracking, discoloration, EPDM, erosion, hydrophobicity, insulators, IPT, silicone rubber, tracking, transmission. 1 INTRODUCTION Composite insulators have been increasingly used in high voltage systems worldwide during the last decades [1-3]; their use reduces the maintenance cost providing similar or better reliability levels to that of ceramic insulators [4, 5]. The field performance of composite insulators depends on many factors, including insulator design, material quality and service conditions experienced. Several diagnostic techniques for condition assessment of composite insulators have been developed, as described in technical brochures [6-9], guides [10, 11], specifications [12, 13] and standards [14, 15]. Emphasis has been given in evaluating, through laboratory tests [16-24] and field experience [25-43], the insulator housing, which is susceptible to field-ageing caused by environmental, electrical and mechanical stresses. Ageing of polymeric materials used for insulator housing is normally evaluated through standard accelerated laboratory tests, involving carefully controlled influencing factors. However, composite insulators in-service suffer from the interactive effects of several uncontrolled ageing stresses, varying in severity with operational and environmental conditions. Thus, knowledge on ageing of composite insulators gained from field experience is of great importance for improved reliability of power networks. This study evaluates field-ageing effects on insulating materials (EPDM and VMQ/HCR) of composite suspension insulators after the same service life of 17 years. Several diagnostic techniques were applied to assess the surface morphological and material degradation as well as hydrophobicity of the polymeric housings. Resistance against tracking and erosion of the insulator housings as affected by field-ageing was evaluated through the inclined plane test (IPT). It is shown that the housing surface material was degraded to different extent between the two field-aged insulators, Manuscript received on 29 May 2016, in final form 16 October 2005, accepted 17 October 2016. Corresponding author: P.N. Mikropoulos. 490 N.C. Mavrikakis, et al.: Evaluation of Field-ageing Effects on Insulating Materials of Composite Suspension Insulators DOI: 10.1109/TDEI.2016.006077