Improvement of electric field distribution by integrating composite insulators in a 400 kV AC double circuit line in Algeria

Abstract

Because of their advantages over glass and porcelain insulators, composite insulators are being used now in power transmission lines for different voltage rating levels. Recently, the 400 kV level is introduced by Societe Nationale de l'Electricite et du Gaz, SONELGAZ (Algerian Company of Electric Power and Gas) where glass insulators are installed. For better electrical performances, we propose in this paper to integrate composite insulators in a three phase 400 kV AC double circuit line situated in the northwest of Algeria. A comparison is done between the already existing glass insulators and the proposed composite insulator in terms of electric field distribution. The electric field is studied along the leakage paths of the insulators under different surface conditions (dry and clean, uniformly and non uniformly polluted, and in presence of water droplets). Three composite insulators with different shed configurations are proposed. From these three configurations, we selected the insulator presenting lower electric field magnitude in critical areas mainly on the triple point junction (air — HV end — housing material interface). On the double circuit line, we focused our study on the phase insulator that presents the highest electrical stress. Impact of hardware fittings, tower, phases and conductors on the electric field distribution has been analyzed. Effects of bundled conductors have been also studied. Simulations were carried out by employing 2D Finite Element Method (FEM) using COMSOL Multiphysics® 4.3 software. Results show that electric field is lower in the case of composite insulators. Furthermore, we found that the calculation model can be simplified by not considering all circuit phases. Note that appropriate corona rings are considered on both HV and ground ends for glass and composite insulators and their geometrical parameters (corona ring diameter, corona ring tube diameter and corona ring height) are kept constant throughout the whole study.