The Research On Fast Algorithm Of Overvoltage Distribution In Power Transformer Under VFTO

Switching operations in Gas Insulated Substations (GIS) may generate Very FastTransient Overvoltage (VFTO) which is a kind of instantaneous overvoltage lasting for afew milliseconds. Its rise-time is less than 0.1 milliseconds and its oscillating frequency is ofseveral megahertz. VFTO is very dangerous for the power system, especially for thetransformer which is directly connected to GIS. In this paper, multi-conductor transmissionline (MTL) model is used to analyze the transient response of transformer windings underVFTO. Using MTL model, a system of large-scale equations will be obtained. Manykinds of Model Order Reduction (MOR) methods are studied. By matching the mainfurther of Amplitude-frequency characteristics of transformer's voltage transfer function andVFTO signal, a fast algorithm is proposed which based on precise calculation of e^Ad andKrylov subspace and ignore the frequency points with minor effect on time domain response.A comparison is made between the calculated voltage distribution and the experimental ones, a good agreement is achieved. Finally, overvoltage distribution in 800kV power transformerunder VFTO is calculated using the algorithm proposed in this paper. The design oftransformer insulation has been verified to be reasonable.