Automatic Stand for Testing the Influence of Humidity and Temperature on Dielectric Charges

Used for their excellent electrical behavior, as well as for their other good general properties, polymers are today applied mostly for the electrical insulation of underground BV/MV power line cables. Observed from the microscopic level, these dielectrics are not homogeneous. They present a mix of amorphous and crystalline volumes and the interface between these regions offers boudary junctions. This microscopic inhomogeneity detemines an increased space charge at the microscopic place. The existence of space charge causes an electric stress enhancement which may reduce the lifespan of the dielectric material. In this paper, partial discharges occurring in an air-filled gap between two closed high density polyethylene cavities are experimentally investigated. Measurements are performed at different temperatures, from 10°C up to 90°C and for different relative humidity ratios, from 20 up to 70%. The influence of these environmental parameters on PDIV, PD phase distribution and occurance numbers is clealy described.