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Very fast transient overvoltage (VFTO) is very dangerous for the transformer which is directly connected to gas insulated substations (GIS). In order to study the voltage distribution in transformer windings under VFTO, a new model named the Piecewise Lumped Parameter (PLP) model is proposed. The piecewise lumped parameter model divides each turn of transformer windings into proper sections, whose parameters are all lumped parameters, including resistance, inductance, capacitance and conductance. The PLP model is the lumped parameter circuit model on section basis. Each section is composed of a new π-type equivalent circuit of lumped circuit model. Comparing with the results by the Multi-conductor Transmission Lines (MTL) model, this paper will summarize the reason for how to divide, that is, the relationship between the length of the section (l) and the length of wave(λ).