Measurement Methods of Accumulated Electric Charges on Spacer in Gas Insulated Switchgear

The phenomenon of accumulated charges on a solid insulator material surface is one of critical parameters at the insulation design stage for ac electric power equipment as well as dc equipment. Therefore, it is important to grasp charge amounts on an insulator surface with an appropriate resolution. Over the last few years, researchers have made tremendous progress on this subject, but reports are rather academic and not always easy for electric power engineers to understand and apply practically. This paper explains latest measurement methods plainly starting with the basic principle of the measurement, supposing mainly gas insulated switchgear (GIS) engineers. It includes inverse-problem-solving as signal processing technique, resolution evaluation from the standpoint of system geometry, sample frequency, and noise. Further, effects of various parameters on the resolution and also preferable measurement systems for, e.g., 500 kV actual GIS spacers are treated.