There is an increasing interest in applying monitoring systems and on line diagnosis techniques to power transformers, as these are one of the most expensive and critical components of a power system. Detecting failures in an incipient stage can avoid major transformer damages, allowing important savings in investing, and giving time enough to plan transformer outages. In recent years, a great number of monitoring systems have been reported. Some of them, make use of models as a tool to assess transformer condition. In this paper the use of a vibration model to be applied to transformer monitoring is proposed. In the paper, a review of the basic theory of transformer vibration is performed and the results of an experimental set of tests carried out in order to establish the model basis are reported.