Air Core Transformer Winding Disk Deformation: A Precise Study on Mutual Inductance Variation and Its Influence on Frequency Response Spectrum

It is well-known that the deformation of transformer winding can produce detectable changes to the frequency response spectrum compared with a referenced past measurement. To interpret such changes for diagnostic purposes, main causes of the trace deviation need to be recognized precisely. In addition, it is useful that the interpretation of transformer frequency response is classified in a way that IoT-based techniques can be developed in the near future to analyze the transformer mechanical integrity. This paper has specifically concentrated on the inductance and capacitance variation due to the axial and radial disk deformation of transformer winding. Analytical analyses on selfand mutual-inductance variations are discussed and capacitance variation is studied in detail for symmetrical and asymmetrical transformer disk deformations. A numerical example is provided to establish the analytical approach and compare inductance and capacitance variation. The analytical approach is finally examined through the experimental study of disk deformation in a 66 kV transformer winding.