Overvoltage protection procedures for high frequency high voltage transformers

Parasitic elements, as leakage inductance and winding capacitance are present in all transformers. If such elements will or won't play a significant role in the transformer's operation depends on the specific application. In high-voltage devices the both cited parameters tend to be more relevant, since the isolation asks for increasing the separation between primary and secondary, while the high secondary number of turns increases the capacitance. In power electronics applications, especially if the primary voltage has squared waveform, the high order harmonics can excite the resulting resonances, producing very high primary current and secondary voltage stresses. This behavior is more relevant when the transformer operates without load, what means, without damping. This paper explores the overvoltage phenomenon and proposes different protection strategies to avoid its manifestation, depending on the transformer parameters. Experimental results validate the proposed strategies.