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

The flashover voltages of a porcelain and a semiconducting glazed insulator are compared. The test samples are stressed with positive lightning impulse (LI) voltage (1.2/50) at four different temperatures (10/spl deg/C, 20/spl deg/C, 30/spl deg/C, 40/spl deg/C) in an environmental chamber. In each temperature step the relative humidity is varied between 10% and 90%. The test results are evaluated over the absolute humidity. A temperature correction is applied to the flashover voltage, to compare the values of the two insulator types over the absolute humidity. The potential distribution along the insulators is investigated by numerical field calculation. The distribution for different frequencies of the driving voltage and for impulse voltages is shown. The flashover behavior of the two different insulator types can be explained by their potential distribution. The flashover voltages obtained with lightning impulse stress are compared to results measured earlier with switching impulse (SI) voltage (250/2500). The differences in the flashover behavior can be described with the potential distribution at lightning respectively switching impulse stress. The advantages and limits of the semiconducting glazed insulator, compared to a porcelain insulator, are described for LI and SI stress.