Charge distribution measurement on a truncated cone spacer under dc voltage

A system for measuring charge distribution on an insulating spacer is developed. An electrostatic probe is set close to the spacer, and it moves along its surface maintaining a small gap. The accumulated charge is inversely calculated from the measured data by utilizing the relationship that is obtained through the numerical electric field computation. Using this system, the surface charge distribution on a truncated cone spacer of 80 mm diameter and 15 mm height is measured. The number of measured points is 3402, and the spatial resolution is 3.9 mm. After the application of dc 10 kV for 19 hours, the spacer surface is charged with a spotted pattern. The charge density reaches 60 pC/mm(2) at its maximum. In addition, the residual charge distribution of partial discharge from metallic particles on the spacer is observed.