An experimental study of surges and oscillations in windings of core-type transformers

Measurements on two experimental core-type transformers, one with two limbs and the other with three limbs, were used to test the validity of theories of transient oscillations in windings with particular reference to Coleman´s theoretical treatment of multi-limb transformers. Wherever practicable, `equivalent single-limb¿ parameters were measured in accordance with this theory. Spectral distributions of oscillation frequencies and variations of mutual leakage inductance between winding elements with separation between elements were adopted as the main criteria in comparisons of experiment and theory. These comparisons showed the superiority of an exponential distribution of mutual inductance over other approximations assumed theories. No critical oscillation frequency as predicted by Rÿdenberg was reached or approached, but some support was found for assuming the velocity of travelling waves to be independent of frequency when calculating inter-section voltages. Measured responses in terms of spatial distribution, amplitude and waveform showed reasonable agreement with theory. The analytical treatment by Coleman of the transient behaviour of multi-limb transformers was verified by numerous tests.