Intensification of Electric Field Stresses in Field Aged 380-kV Composite Insulators Due to Loss of Hydrophobicity

Polymer based composite high voltage insulators (HVIs) due to their hydrophobic surfaces have consistently outperformed the traditional ceramic insulators in highly contaminating coastal-desert environments. However, the harsh environment causes polymer surfaces of these HVIs undergo rapid ageing leading to permanent loss of hydrophobicity. In this paper, we have presented three samples of 380 kV composite HVIs with a service life of over ten years near west coast of the Kingdom of Saudi Arabia. Material investigation using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy revealed substantial surface deterioration and change in the composition. Hydrophobicity investigations revealed that surface of the HVIs have become hydrophilic leading to accumulation of continuous films of water. Electrical withstand strength was evaluated using steam fog test showing significant decrease from the rated values. The distribution of electric field around an insulator is a key design criterion for HVIs. The consequences of loss of hydrophobicity on the electric field distribution across insulator surface is explained analytically and through numerical simulations based on Finite Element Method (FEM). The pristine and field aged HVIs are modelled and were covered with realistic water distributions observed during hydrophobicity tests. It has been observed that the intensity of electric field on field aged insulator surpasses the corona inception threshold at certain areas of the insulator, resulting in the initiation of corona discharge on the insulator's surface. This corona inception further causes surface deterioration and accelerated ageing in composite HVI.