Voltage and current transformers fro calibration purpose : reduction of non-linear effects by means of input signal processing

Precise measure of voltage/current is a vital task in electrical sector, for this reason, existing voltage/current pre-processing techniques have to be continuously improved in terms of accuracy, cost, power loss and size. In this thesis a new solution to increase the performance of generators for the calibration of MV measurement transformers has been deeply tested. The aim of the proposed method is to reduce the harmonic distortion produced by the generator thanks to a proper digital pre-processing of the voltage/current input signal. The proposed voltage/current signal, developed in low-voltage, medium-voltage and current transformer system comprises different situations, and a dedicated modulation of the input signal is introduced in order to strongly reduce the effect of the non linearity of the magnetic core of the step-up transformer used inside the generator. It is well known that remanence has some limitations concerning linearity, accuracy and range of operation. When operated a pure sinusoidal signal, the distortion does vary slightly over harmonics, they must be noticed and reduced when a high degree of measurement accuracy is needed. This thesis validates the modulation method for generating signals. Also the investigation under different conditions and an input signal modulation technique has been introduced and tested in order to limit the remanence effects. Finally we have characterized a current generator able to permit to test the frequency response of some Hall Effect Transducers that are under development in the department lab. In particular, the efforts of this part of the thesis activity have been concentrating on the bandwidth extension of the generator.