Fast Time-domain Algorithm of Very Fast Transient in Power Transformer Windings with Wound-in-shields

In order to calculate the overvoltage of transformer windings under the very fast transient overvoltages (VFTOs) more efficiently, a fast time-domain algorithm is presented based on the compact finite difference (CFD) and the backward differentiation formulas (BDF) in this paper, in which a hybrid model is used consisting of multi-conductor transmission-line (MTL) and equivalent frequency-dependent lumped impedance. By means of CFD and vector fitting (VF), the MTL telegrapher's equations with frequency-dependent parameters are discretized spatially, and the lumped impedance is converted into state equations. The resulting equations are solved by the backward differentiation formulas. Because of the small segment number in the CFD and the high precision of VF, the proposed algorithm can calculate the overvoltage along the windings much more efficiently than traditional frequency-domain algorithm and the result is verified by measurements of the winding model.