Wave Phenomena in High-Voltage Windings of Transformers

Determination of mechanical condition of transformer active part can be performed utilizing frequency response of the windings. Many computing models were developed to evaluate behavior of the winding in wide frequency range using different numerical methods. Most of them utilizes finite elements, assuming axial symmetry, if possible. In other cases we need to use a three-dimensional model, which results in a significant reduction in the accuracy of modeling the geometry of the system, as well as the penetration of electromagnetic field into conductors. From a practical point of view, using computer of average performance, the windings can be modeled with at most 10 turns. From this reason mixed models are proposed, where the electric parameters of the winding are concentrated in the substitute RLC elements. Such models are known as "lumped parameter models". Since the parameters of real winding are distributed, the question arises concerning the necessity of taking into account wave phenomena in them. The method allowing this is known as "transmission line method". Measurements of frequency response are used in industry. There are still many problems with interpretation of test results. Computer modeling may be a helpful tool allowing to understand relation between the geometry of a winding and its frequency response. To fulfill this, models should give similar response as a real measurement. The paper describes a modified transmission line method used for modeling of a transformer winding's frequency response. There is described the model, its parameters, and exemplary solution compared to test data.