Project Goals and Objectives – Expected results

Polymer based outdoor insulators have become in the last decade very popular in high voltage applications, steadily increasing their marketshare when compared to the traditional insulators made of porcelain or glass. This is because the composite construction of these insulators, based on a load bearing glass fiber reinforced (GFR) epoxy rod covered with an elastomeric housing, can provide desirable properties. Lighter in weight, they are suitable for areas with pollution and are less demanding on inspection requirements with reduced installation and maintenance costs. Different polymeric materials have been used for the housings of composite insulators in order to achieve improved protection against external environmental factors, the most attractive one currently being the commonly named silicone rubber (SIR). Housings made of SIR can provide long-term hydrophobic properties on the insulator surface as well as the ability to recover their hydrophobicity, a property significantly increasing the reliability of the insulator in highly contaminated areas. This is because in a hydrophobic material, water molecules form discrete droplets on the surface of the insulation with high contact angles, a behavior not allowing the formation of a water layer that could lead to the flow of currents over this surface, resulting eventually in arcing, material damage and even flashover events. This can happen in a hydrophilic surface, which can be formed for example by pollution, leading in the formation of contamination layers and subsequent malfunction. Therefore, the existence and the recovery of the hydrophobicity on composite insulators is a very important feature, even though this recovery process becomes less effective as the polymeric material ages or is degraded. 
An extended incorporation of polymer based outdoor insulators in high voltage systems requires both the assurance of a good and long term stability of the hydrophobicity of the insulator as well as a timely diagnosis regarding their performance. Ageing, degradation and flashover are today the main reasons for failure of composite insulators, the respective mechanisms being different than those in traditional ceramic systems. This is mainly due to the different chemical composition, the higher hydrophobicity of the polymeric surfaces of composite systems and the different ageing characteristics. Existing studies have partially verified the ageing and degradation mechanisms for SIR. However, there is still the requirement for a better understanding of these mechanisms and especially a clarification of their dependence on the environmental condition of a particular region. Moreover, since most of the testing and approval techniques employed have been derived from long experience with the ceramic materials, these are not directly applicable to the composite materials. Therefore, it is important for the technology today to develop suitable diagnostic techniques, allowing the remote and real time evaluation of the functionality of composite insulators, as well as materials suitable for particular environmental conditions. 
The aim of diagnostics is to get relevant information about the state of a technical system. In insulator applications this means that diagnostics should be an aid in making decisions about if and when maintenance or replacement should be done. This is directly related with reducing costs and minimizing risk of damage to people, property and environment. For insulators made of glass or porcelain, several inspection methods are available to detect faulty parts in service. In the case of composite insulators, the situation is more complex. Though several techniques have been proposed for assessing the state of insulators in service, it is still difficult to accurately correlate measured parameters with presence of defects or ageing. For some end users, this lack of appropriate diagnostic methods is claimed as one of the disadvantages. Thus work on developing suitable diagnostic methods and tools for evaluation of the composite insulator conditions must intensify.
For the investigation of the performance of a system, techniques employing light can be favored since non-destructive measurements can be carried out resulting in noncontact and remote recordings of the system properties. For example, laser radiation can be used for sensitive elemental or chemical analysis of samples with spectroscopic methods such as Laser Induced Fluorescence and Laser Induced breakdown Spectroscopy, the respective application including medicine, the environment, artwork conservation and many others. In addition, Spectral Imaging can enable the determination of structure and organization of a sample surface, allowing the recognition of the state of the material as well as its properties.
In this project we aim to investigate in a systematic way the performance of polymer based outdoor insulators used in high voltage applications under the climatic conditions of Crete and Greece and to develop a remote and real time diagnostic tool for the on-the-field evaluation of their functionality. Towards this end, we will initially determine the physical/chemical parameters affecting the functionality of the insulators, and follow up with artificial and field ageing so that the influence of ageing on the basic characteristics and the functionality of the insulators will be better investigated and understood. Afterwards, the performance of various optical techniques (like Spectral Imaging, Laser Induced Fluorescence and Laser Induced breakdown Spectroscopy) will be examined regarding lab and field scale recognition of the functionality of the insulators. Upon deciding on the more appropriate diagnostic technique, the respective model correlating the diagnosis results with basic characteristics and functionality of the insulators will be developed, tested and optimized. Finally, a prototype diagnostic tool will be developed and tested as well as new polymeric material will be designed, exhibiting properties suitable for outdoor composite insulators.
The expected results include the compilation of a significant body of scientific/technological information regarding the influence of ageing of outdoor composite insulators on their functionality in the climatic condition of Crete and Greece and an innovative diagnostic system, generally applicable, for the remote and real time evaluation of the insulator functionality so that decisions regarding maintenance or replacement of the insulators can be made.