Time-domain Calculation Of Transformer Windings Overvoltage Under VFTO Considering Frequency-dependent Parameters

Multi-conductor Transmission line (MTL) model based on the representation of the winding by its individual turns is used to analyze the transient response of transformer windings under Very Fast Transient Overvoltages(VFTO). This paper studied the overvoltage of transformer winding under VFTO in time-domain. Compact Finite Difference (CFD) is used to spatial discrete the MTL model of transformer winding; Vector fitting and recursive convolution are applied to process the frequency-dependent parameters in time-domain. Base on proposed theory, this paper simulates wave process in transformer windings with the Precise Integration Method (PIM) and Backward Differentiation Formulas (BDF) separately. A good agreement is achieved between the measured and calculated results. Because time-domain methods can process problems with nonlinear elements, this paper calculate the transformer windings with Mental Oxide Varistor (MOV) for inner protection. In last part, this paper has studied the time-domain model-reduction based on Krylov-subspace techniques.