The Study On Modeling And Simulation For The Transformer Windings Under VFTO Based On Order Reduction Algorithm

Very fast transient overvoltage (VFTO) can be generated at the switching operation of a disconnector in GIS. This steep voltage may cause serious malfunction or even damage to transformer, especially the transformer directly connected to the GIS. In order to carry out the research on the effect of VFTO to transformer, it is very necessary to establish an appropriate model of the transformer windings under VFTO. By this model, the voltages distributions of transformer windings under VFTO can be calculated by computer. Pade approxmation was used to reduce the orders of the original system transfer functions in establishing the lumped circuit model of the transformer windings under VFTO, but it can not guarantee the stability and accuracy of the reduced system. To address this issue, the transfer functions are firstly converted to state equations. Then Arnoldi algorithm is presented to reduce the orders of the state equations in this paper. The simulation results have proved that the accuracy becomes better and better with increasing the model orders, which Pade-based methods fail. It also demonstrates that the proposed approach is feasible for establishing lumped element equivalent circuit of the transformer windings under VFTO.