Overvoltage distribution calculation of transformer windings under VFTO considering frequency-dependent parameters via Krylov subspace technique

Very fast transient overvoltage (VFTO) is very dangerous for the transformer which is directly connected to gas insulated substations (GIS). In this paper, the multi-conductor transmission line (MTL) model is used to analyze the overvoltage distributions of transformer windings under VFTO. A fast algorithm based on precise integration method (PIM) and Krylov subspace technique is proposed. Furthermore the points with its frequency greater than 20 MHz can be ignored for more computational efficiency. A test core-type transformer winding is studied, and there is a good agreement between the simulation results and the measurement ones. The algorithm used in this paper is about 8 times faster than the traditional frequency-domain algorithm. Furthermore, overvoltage distributions in 800 kV power transformer under VFTO are calculated.