Measurement of very fast transient overvoltages at the transformer entrance

Disconnector switching operations in large gas insulated switchgear (GIS) systems may cause very fast transients overvoltages (VFTO). These VFTO surges produce dielectric stress to other apparatus of the substation. This paper presents the test technique for measuring VFTO at the transformer entrance. A VFTO sensor is installed at the end shield of transformer bushing. Deconvolution based on the incremental Wiener filter which is used to reconstruction the input transient voltage is also described. To check the characteristic of the VFTO sensor, a fast transient simulation platform is build. Results of the measuring experiments are introduced at the end of this paper.