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Report RSE 17006677

Diagnostic methods and optical sensors for Power Transformer diagnostic



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N. Cennamo (Università della Campania), L. Zeni (Università della Campania), J. Borghetto (RSE SpA), L. Cice (RSE SpA), M. Pesavento (Università di Pavia), L. De Maria (RSE SpA)

MON4-GRID 2017 - Management, monitoring and control of the transmission grid

Analysis of the degradation processes of the transformer's solid insulating system and description of the non-traditional electrical and innovative optical-type diagnostic techniques identified for an integrated approach to this problem. Results of a first temperature experimentation, with the proposed methodologies, on different types of specimens representative of the paper-oil insulation, subjected to different conditions of humidity and degradation.

The power transformer is a key element of the power grid; out of service of this component, as a result of a failure, causes serious customer misconduct and undesirable economic damage. In this report, main causes of the degradation of the solid insulating system of transformers have been analysed, with particular reference to the accelerated ageing of the insulating paper and to the presence of corrosive sulfur. A review of the main diagnostic tool, traditional, non-traditional ones, and the innovative optical technique, was presented.

The joint use of these methodologies will allow a complementary approach to the analysis of degradation phenomena of insulating paper-fluid systems (paper/ mineral oil or natural ester or synthetic ester). During the period of reference, temperature tests were carried out on different types of paper-oil specimens, subjected to different conditions of humidity and degradation, by means of the new electrical method (implemented in the DIRANA system) and by the optic resonant one (implemented in Surface Plasmon Resonance_ SPR sensors and on a MIP-Molecular Imprinted Polymer synthetic receptor).

In this reports first results and their comparison with data of chemical-physical analysis are reported; some important indications on test procedure and on parameter settings to correctly fit the dielectric dissipation factor (DDF) response as a function of the frequency are discussed.Concerning the optical SPR sensor response, it has been verified that it is not affected by the nature of the specimen and by its thermal treatment: the concentration of solid insulation by-products, measured by the new SPR sensors, are in a semi-quantitative agreement, with data acquired by standard methods (HPLC-High Performance Liquid Chromatography). In the same period, a new optical system architecture based on two cascaded SPR- sensors with different thicknesses of the gold layer has been proposed.

As a proof of principle, the possibility of simultaneous determination of two important analytes, dibenzyl disulfide (DBDS) and furfural (2-FAL), in mineral oil matrix was investigated. Main features of the SPR-MIP sensors, like low cost, high selectivity and sensitivity, together with the simple and modular scheme of the new cascaded interrogation system make this method potentially suitable for on-line multi-analyte application.

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