Material Analysis of Composite Hollow Core Insulator Housings after Long-Term Ageing Test

CHCIs under these specific conditions. The focus here is on the housing material, as it performs the main insulating function to withstand specific environmental conditions.

To test products and materials for high-voltage equipment, long-term tests can be performed at the EDF LME (Laboratoire des Matériels Électriques) in Martigues, France. Two 420 kV

CHCIs with housing materials from different suppliers were installed at the test station, one with HCR (high consistency rubber) silicone housing in 2008, and one with LSR (liquid silicone rubber) housing in 2015. The aim was to evaluate the long-term service performance under severe conditions: intense UV radiation, precipitation, marine and industrial pollution. Results of investigations over the year have been presented in several conference papers [1, 2, 3, 4, 5].

After several years of observations and inspections, the test was completed at the end of 2023 and final investigations after dismantling is aim of this contribution.

After deinstallation, specific insulator tests have been performed to examine the overall condition of the CHCIs: visual examination, peel-off test of silicone housing, pressure type test. Apart from a few partial discharge and superficial erosion traces at the HCR housing and a global pollution layer on the housing surface, the insulators remained fully functional without any significant damages. The HCR silicone became brittle over the years and sheds got broken in case of mechanical stress like manual bending. For both silicone materials, the peel-off test revealed consistent and strong adhesion. A pressure type test was performed to investigate the adhesive joint between the aluminum flange and the composite tube – no signs of aging were detected.

After the insulator tests, material analyses of the housing materials provide detailed information about the condition of the silicones after the long-term test: A water diffusion test on core with housing confirmed the resistance to water attack and electrical efficiency of the core to housing adhesion, contact angle measurements classify the hydrophobicity, and a fingerprint analysis confirmed no changes towards degradation in the formulations of the silicone materials.

Additionally, a more detailed analysis of the pollution layer was conducted by SEM (Scanning

Electron Microscopy), EDX (Energy-Dispersive X-ray Spectroscopy) as well as measurements of the partial layer conductivity. The detected chemical elements in the pollution layer are typical for the surrounding environment and industry at the test station and confirm the high level of pollution.

As a conclusion, a proper material selection and reliable insulator design with respect to tests under environmental conditions can be verified by conducting full-scale product tests in test stations. In the specific case, the overall positive test results after operation in Martigues test station are in good agreement with the reliable service experience of CHCIs in France. If selected and designed properly, CHCIs with LSR and HCR housing materials can be operated for years and decades without any relevant loss of insulation or product performance even under severe environmental conditions and industry pollution.