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Electrical current measurement based on elastic waves propagation in dielectric materials

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Testing a new type of transformer

Electric current measurement transformers are crucial to the generation, transmission and distribution of electrical energy and control the flow of power in any electrical grid. However, these vital pieces of equipment for measuring electrical magnitude are still manufactured using almost the same technological concepts and methods as 40 years ago.

Energy

The IELAS consortium developed a new type of current measurement transformer, which operates using mechanical waves rather than magnetic flux variations. A full-scale prototype was produced, based on magnetostrictive and piezoelectric materials instead of copper coils and a magnetic core. Magnetostriction involves changes in the shape of ferromagnetic materials when subject to a magnetic field. Piezoelectricity is the ability of some materials to generate an electrical potential when mechanical stress is applied. This new approach allowed researchers to significantly reduce the size and weight of the transformers and to stop using mineral oil for cooling and insulating the windings. These changes mean that manufacturing costs are dramatically lower than for an equivalent conventional current transformer. The industrial production of these devices would enable manufacturers to achieve a major competitive advantage and help boost the European economy. Tests on the full-scale prototype were carried out in two phases. The initial phase characterised the sensor behaviour under different operating conditions of up to 3,000 amperes. It was concluded that further studies of the magnetostrictive material were needed in order to achieve repeatability of results. The electrotechnical design of the sensor ensured the stable alignment of the one metre stack. The stack comprised the magnetostrictive emitter, the piezoelectric receiver and the connecting alumina bar. The second testing phase involved a series of standard high voltage tests. These are performed on all electrical equipment that is installed in an electrical substation and operated at the usual voltage ratios of up to 400kV. The transformer successfully withstood the lightning impulse test and the power frequency test. These were necessary for ensuring that the integrity of the transformer's insulation was not compromised.

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