The paper examines the effect of residual flux on switching transients in single-phase and 3-phase transformers, both experimentally and by calculation. Ferroresonance in single-phase and 3-phase transformers is also studied, with particular reference to the various modes, e.g. subharmonic. The basic equations for the transformer have been extended to include the effects of capacitance. The external circuit model used corresponds to a simple representation of capacitively-coupled transmission lines. Experimental and computed results are presented.