Computation of Very Fast Transient Overvoltages in Transformer Windings

Abstract

The algorithm uses a modified continuous Fourier transformation that provides an accurate time domain computation. As an example, the interturn voltage distributions for two 500-kV autotransformers are computed and compared with measurements provided by other publications.

Analysis of Very Fast Transients in Layer-Type Transformer Windings

“…A practical solution is to reduce the order of the matrices. This can be achieved by grouping a number of turns as a single line so that the information at the end of the line remains unchanged, as in the case when separate lines are used [8], [9]. This approach is used for layer-type modeling.…”

“…The occurrence of VFTO in a large shell-type transformer was reported in [8] and [9], where it was demonstrated that internal resonances occur and that interturn voltages can rise to such a high value that an insulation breakdown can take place. Multiple reignitions can occur during the switching of transformers and motors with vacuum CBs (VCBs), because of the ability of VCBs to interrupt high-frequency currents.…”

A frequency domain transformer model for simulating fast transient overvoltages

“…The following voltage and current relations can be written from − Substituting equations (6) in (3) and reducing through matrix operations, the terminal voltages and currents are given by [7]:…”

“…The inductance is calculated considering that the turns are similar to a lossless transmission line where the propagation depends on the dielectric and magnetic properties of the winding, then [6]:…”

“…The most of models are based on equivalent lumped circuits with coupled inductances and capacitances [4,5]. Some models have been developed using transmission line theory, which has the advantage of including more easily the frequency dependent phenomena and the distributed parameters of the winding [2,6].…”