Flashover behavior of semiconducting glazed insulators under positive switching impulse stress at different climatic conditions

This paper deals with the flashover voltage of semiconducting glazed insulators under positive switching impulse stress. The measurements are carried out with clean insulators. The results are compared to those obtained earlier with porcelain and composite insulators to show the benefits of the semiconducting glazed insulator technology. All tests are performed in an environmental chamber. The temperature is ranged between 10°C and 40°C in steps of 10°C. In each temperature step the relative humidity is varied between 10% and 95%. The behavior of the flashover voltage is evaluated over the relative and the absolute humidity. A temperature correction factor is given. The sole influence of the absolute humidity on the flashover voltage can be derived after applying the temperature correction to the measured values. The different flashover behavior of the semiconducting glazed insulator can be explained by its changed voltage distribution. Therefore the potential distribution along the semiconducting glazed insulator is measured with AC, DC and different impulse voltages. From the measurements and a field calculation a simple equivalent circuit is developed to calculate the potential distribution for various voltage stresses