AbstractA reliable technique is needed for accurate measurement of very fast transient overvoltages such as disconnector‐induced surges occurring in GIS which have very steep front and high‐frequency oscillation. Recently, capacitive voltage sensors with very short response times have been proposed for this purpose. However, few studies have been made on the dielectric properties of materials used for a low‐voltage‐side capacitor, as well as the frequency bandwidth of the measuring system.In this paper a thin mica plate is proposed for a low‐voltage‐side capacitor which has a surface coated with silver on both sides. This material has been shown to have stable and high static capacitance up to a high‐frequency range. A quantitative estimate also is given for the frequency bandwidth of the measuring system. Furthermore, a practical‐scale sensor of this type has been developed which can successfully measure simulated disconnector‐induced surges of several hundred kilovolts under similar conditions in GIS.