Flashover behavior of ceramic and non-ceramic insulators under switching impulse stress at different climatic conditions

Composite insulators became more and more common in service to replace porcelain insulators, because of their outstanding surface characteristics in polluted areas. Many investigations have been carried out on their behavior under AC and DC stress. Little data is available for impulse stress. Therefore the flashover behavior of a ceramic and a composite insulator were investigated under different climatic conditions and switching impulse (SI) stress. The temperature was varied between 10°C and 40°C. The relative humidity was ranged between 10% and 90%. All tests took place in an environmental chamber. The insulators were manufactured with the same profile of the electrodes and had the same number of sheds to get results which were easy to compare. The tests were performed with clean insulators. The influence of the relative and absolute humidity on the flashover voltage were evaluated with respect to the different insulator materials. The results were compared to those obtained in the pure air gap. Special attention was paid to the statistical analyses of the data, which means how to calculate errorbars and confidential intervals