Determining a ‘Health Index’ for Field-Aged Composite Insulators


High-temperature vulcanized silicone elastomers have become the preferred housing material for high voltage outdoor insulators and are increasingly used on overhead lines worldwide. Among other factors, this has been due to their outstanding properties such as hydrophobicity, hydrophobicity recovery and hydrophobicity transfer. These properties significantly reduce formation of conductive contamination layers that can lead to increased discharge activity and pollution flashover. Their high resistance to electrical discharges and erosion is yet another benefit.

These important properties have been tested for decades using standardized test procedures, with particular attention paid to ageing resistance. Ageing of insulators during operation can lead to sudden mechanical or electrical failure, which can result in dangerous situations with potentially huge impact on the network and a corresponding interruption in energy supply.

Fig. 1: Methods to evaluate ageing of composite insulators.

TenneT, a cross-border transmission system operator in Germany and the Netherlands operates over 23,500 kilometres of high voltage connections and ensures a secure supply of electricity to more than 42 million end-users. In this regard, a systematic approach is applied to assess the reliability of all elements installed on the network. This approach involves determining and assigning a so-called ‘Health Index’ for each component of the grid. Based on visual and laboratory-based assessment carried out on a statistically significant number of components, such as insulators, this health index for any specific line segment is generated and evaluated in a visual overview.

A large part of the TenneT grid is still equipped with porcelain insulators and the procedure for their assessment has already been well developed. However new lines are now being built mostly with polymer insulators and, for this component, the process of assessing a health index has still needed to be fully defined.

Fig. 2: Evaluating formation of cracks on polymer insulator surfaces.

Attend the 2022 INMR WORLD CONGRESS in Berlin where experts from TenneT TSO will offer a detailed overview and assessment of laboratory test data as well as sampling and inspection methods used to develop a ‘Health Index’ for the new generation of polymer insulators.