High Frequency Modeling of Foil Type Transformers for Shipboard Power Electronic Power Distribution Systems

In shipboard applications, oil cooled transformers have been replaced by more compact and environment friendly dry-type transformers. Among the latter, the foil-type are spreading due to faster and easier manufacturing and design, substantially reducing their final cost. Along with new transformers, power electronic devices are becoming ubiquitous in onboard applications. However, these two technologies have shown a certain degree of incompatibility due to the fast switching commutations of the static converters that affect the insulation system of the connected machines and components. Indeed, an increasing failure rate in power transformers supplying electronic power converters suggests that the fast voltage transients produced by the converters, combined with the proximity induced by onboard space availability, can excite destructive resonances both inside the transformer and in the converter-cable-transformer system. In order to develop a design methodology aimed at avoiding resonance related issues in shipboard power systems, a full characterization of all system's elements is necessary. In this paper, a model to study high frequency phenomena in foil-type transformers is presented. In particular, it is shown that the foil geometry induces unique characteristics in terms of resonance modes and behavior towards fast transients, due to their peculiar structure.