Experimental evaluation of the limit condition for tap-staggered autotransformers through noise and vibration analysis

The growing demand for electric energy and the development of green sources such as photovoltaic and wind power are requiring the integration of new systems in the already developed transmission network. This task is not always straightforward, since when a large amount of power is not used, it gives rise to reactive loads. Usually, to put back into phase the voltage and the current, specific devices such as reactors are applied at the electric station level. One of the practices that are becoming increasingly common is the use of two autotransformers adopting the tap-staggering technique. In this way, already existing devices can be used to rearrange the electric line parameters. One of the downsides is that, related to the specific design of the transformers, high magnetic flux can occur in the core. Due to overexcitation, vibrations generated by magnetostriction can become extremely high and can bring to damages that in some cases can cause an impairment of the device. This article aims to find suitable parameters able to predict the approaching of a limit condition beyond which the autotransformer can undergo damage. For this purpose, experimental investigations considering the vibrations and the noise emitted by five autotransformers were carried out in different tap staggering conditions. It was found that the acceleration values very much depend on the position of the transducer, while the acoustic noise measurements give an average of the sound radiated by the different parts of the autotransformers but depend on the distance from the case of the device. For this reason, it is advised not to exceed an average overall value of 80 dB(A) sound pressure level at a 2 m distance from the autotransformer.