Wide-band modelling of an air-core power transformer winding

[摘要] ENGLISH ABSTRACT: The objective of this project is to develop an electromagnetic model that can be used toaccurately calculate the voltage distribution in a transformer winding structure when excitedwith standard impulse excitation waves. This voltage distribution is required during thedesign stage of a power transformer to ensure that the insulation is capable of withstandingthe occurring electric field stresses during these tests. This study focuses on the modellingof a single disk-type power transformer winding without the presence of an iron-core.Methods of calculating self- and mutual-inductances of transformer windings are presentedand validated by means of finite element method software simulations. The same is done forthe calculation methods used for calculating the capacitances in and around the windingstructure. The calculated and FEM-simulated results are compared to measured values as afinal stage of validation. The methods used to calculate the various model parameters seemto produce results that agrees well with measured values. The non-linear frequencydependant dissipative nature of transformer windings is also investigated and a methodologyto take this into account is proposed and implemented. The complete modellingmethodology proposed in this thesis, which includes the calculation of the modelparameters, model synthesis and solver algorithm, are applied to an actual case study. Thecase study is performed on an air-core reactor manufactured using a disk-type powertransformer winding. The reactor is excited with standard lightning impulse waves and thevoltages along the winding are measured. The calculated and measured voltage waveforms are compared in both the frequency and time-domain. From the comparison it isfound that the model accurately represents the actual transient voltage response of the testunitfor the frequency range of interest during standard factory acceptance tests.

[发布机构] Stellenbosch University