Comparison between the high frequency characteristics of transformer interleaved and ordinary disk windings

Interleaved and ordinary disk windings are widely used in high voltage transformers. Due to the difference in their inter-turn connections, the behaviours of electromagnetic transients in these windings are very different, especially at high frequencies. Although several winding models have been developed in the world for the calculation of impulse voltage distributions along transformer windings, no work has been done to determine the detailed high frequency characteristics. The authors have examined an interleaved and an ordinary disk winding of the same size and structure using a new transformer model and software package developed by Electricite de France. It has been found that for the interleaved winding, there exists a certain frequency range in which the winding behaves as a capacitive ladder network. However, the ordinary disk winding does not show such a frequency range. This result agrees with the previous measurements on several 66 kV to 220 kV power transformers. Comparison has also been made for these two windings in their impulse and sinusoidal voltage distributions. From theoretical analysis, an explanation is given to the difference of high frequency characteristics between interleaved and ordinary disk windings.